Rosette disease in roses

Contents

This regular organic treatment is keeping rose rosette disease at bay

Question: I spoke with Howard on the radio in August of 2015. My 100-plus-year-old Seven Sisters rose bush had rose rosette disease, and I was crushed. I’m the fourth generation to have this rose bush. It’s lived in Muenster, Gainesville, Dallas, and now Plano. And I lost its only propagation the year before to rose rosette disease, but didn’t know what it was at the time. I thought the small leaves and blooms were a result of the drought, and didn’t pursue treatment. When the original bush started showing the same signs, I researched, and felt awful for inadvertently letting the other bush perish. I followed Howard’s treatment plan, and it works! During a busy time I missed a treatment or two, and the disease flared back up. But regular treatment is keeping it at bay. — V.J., Plano

Answer: Thanks for the good report. We’ll pass the good news on. The critics, of course, continue to say that there is no cure.

Roses recovering from rose rosette disease.(Reader photo)

Question: We live on an acre with open fields on all sides. We have been organic since we moved here 16 years ago. We have been invaded by a tiny bug I cannot get rid of. There are millions of them. They are about 1/8-inch to 1/4-inch long. They are white, almost clear. They fly very quick so it’s hard to get a good look at it. A lot of the foliage turns colors like a bacterial disease. I have sprayed mound drench, insecticidal oil, cedar oil, garlic with orange oil — all with no improvement. Any suggestions? Thank you. — P.M., Benbrook

Answer: If you can catch any, send them to the A&M extension office for positive identification. I’m not sure what they are. The various organic tools you have used are what I would have recommended you try. Once we have a positive ID, maybe I can come up with another idea. In the short term, you might try one of the products that contains spinosad.

Question: Most books recommend keeping milk products out of compost piles or worm bins. But what about clearish-appearing whey from homemade yogurt? Can I compost that? — T.K., Dallas

Answer: Those books are giving out bad advice. Any milk, whey, yogurt or cheese products make effective and appropriate ingredients for the compost pile. I’d let them break down some first in metal containers along with other scraps from the kitchen and dinner table before placing in the open piles. That keeps the wild animals away.

Question: My St. Augustine grass has what appears to be the fungus brown patch. Is it too late in the year to treat? — D.O., Dallas

Answer: It would probably be good to go ahead and apply the whole ground or horticultural cornmeal at 20 pounds per 1,000 square feet. Even though the growth is over for the year, the stimulation of the beneficial trichoderma fungus now will lead to healthy turf next spring. Stop watering and fertilizing if you haven’t already.

December organic maintenance

Plant:

* Cool season annuals and hardy perennials. Delphiniums, larkspur and poppies from seed. Many cool season transplant choices are available.

* Trees, shrubs, vines, ground covers and other crops such as arugula, cabbage, kale, chard, greens, spinach and lettuce. Carrots and garlic can still be planted.

* Herb transplants including lavender, oregano, rosemary, rue, sage, parsley, coriander, dill and fennel. Dill and fennel may need some freeze protection

* Living Christmas trees (after use) that are adapted to the area’s climate and soils.

* Spring bulbs, including tulips and hyacinths.

* Transplant shrubs and trees.

Fertilize:

* Avoid all synthetic fertilizers, of course.

* Cool season annuals in beds and pots. Use Garrett Juice as a soil drench fertilizer.

* Greenhouse plants if needed with organic fertilizers, earthworm castings and lava sand.

* Houseplants, once during winter, with earthworm castings, lava sand and other odorless organic fertilizers. Coffee grounds are one good choice. Add apple cider vinegar at one tablespoon to one ounce per gallon at each watering.

* Winter grasses with mild organic fertilizer at one-half the rate, usually 10 pounds per thousand square feet.

* See the Organic Fruit and Pecan Tree Program on the homepage of DirtDoctor.com for details on these trees.

Prune:

* Do not prune the tops of crape myrtles. The seedpods are decorative, and some small birds like the seed.

* Evergreens, to adjust the appearance.

* Do not make flush cuts, and do not apply pruning paint to any plants.

* Shade trees to remove dead, damaged, and out-of-place limbs. Do not prune just to “thin out” trees. Trimming can be done to avoid crowding and to allow more light to understory plants and to eliminate co-dominate vertical growth.

* Cut off tops of spent perennials if not already done. Leave roots in the ground.

* Wait till the end of the winter to prune fruit trees and grapes. Best timing for them is just before bud break to prevent premature flowering.

* Use the dormant months to remove ground covers from the bases of plants and vines completely from all trees. If soil is on the root flares and trunks of trees, remove the soil very carefully with slow water, a stiff broom and a shop vac. It’s best to hire an arborist to do the work with the air spade.

Maintenance

Water:

* Potted plants as needed.

* Any dry areas to help protect against desiccation and winter cold injury.

* Add apple cider vinegar at one tablespoon to one ounce per gallon, time permitting.

Pests:

INSECTS: Spray houseplants with liquid seaweed, mild soap and bio-stimulants to control scale, mealy bugs, spider mites and other insects. Mild orange oil-based mound drench solutions can also be used.

Bark aphids on trees look scary but normally need no treatment.

Spray heavy infestations of scale insects on shade and fruit trees with horticultural oil. Not recommended except in extreme cases. Sprays will kill beneficial insects and microbes.

Avoid all toxic chemical pesticides, as usual.

DISEASES: Spray garlic tea on plants with fungal diseases. Apply dry granulated garlic to the soil for addition control. Spray BioWash.

WEEDS: Remember that henbit, clover, and other wildflowers are beautiful; so don’t worry about spraying them in most cases. If you must, spray vinegar, orange oil and fatty acid products between Christmas and New Year’s. See appendix for formula.

Cut mistletoe out of trees. Remove infested limbs if possible. Apply the Sick Tree Treatment. Also apply the Sick Tree Treatment to other stressed trees such as those with heavy infestations of galls.

Odd jobs:

Continue to mulch leaves into the turf.

Cover tender plants before freezes with floating row cover. Potted plants can be covered with large plastic trash cans.

Pick tomatoes the night before first freeze, unless they are already gone.

Clean and oil tools before storing for winter.

Run mower, trimmer engines dry of gasoline. Drain and change oil. Take to repair shop now to avoid the spring rush.

Mulch all bare soil. Apply a thin layer of compost followed by shredded native tree trimmings.

Turn compost piles as time allows. Add molasses to speed up breakdown.

Apply lava sand or decomposed granite on icy paving. Do not use chemical deicers, salt or synthetic fertilizers.

By: Kevin Ong, Molly Giesbrecht, Dotty Woodson and Laura Miller

What do we know?

Rose rosette disease, a lethal rose disease with no known cure, has recently increased in the Dallas-Fort Worth area. Many people who grow and enjoy roses as well as landscapers who take care of them are concerned about how to protect their plants and confused by all the information available from various sources on the Internet, in publications, and from the media.So, what do we know about this disease?

The following review of information from peer reviewed (evaluated by experts in the field) articles in scientific journals summarizes what we know so far. The disease has been around for more than 70 years. As early as the 1940s, symptoms of witches’ broom (growth of a tight, brush-like cluster of plant shoots) (Fig. 1) were described on roses in Manitoba, Canada (Conners, 1941). In the United States, rose plants in Wyoming with similar symptoms were described in 1942 (Thomas and Scott, 1953), and the disease was subsequently found in other states. In 1990, George Philley reported the disease in East Texas. It appeared in the Dallas-Fort Worth area in the mid-1990s and has expanded there in the last 2 to 3 years.

Symptoms associated with rose rosette disease include:

  • Witches’ broom (Fig. 2)
  • Malformed flowers and leaves
  • Excessive leaf growth and thorniness
  • Extreme red discoloration of plant tissue (Fig. 3)
  • Lateral shoot elongation (abnormal lengthening of side branches/twigs)
  • Enlarged/thickened stems

However, symptoms vary on different rose types and cultivars. For example, red shoots do not occur in some ornamental rose varieties, and multiflora roses do not exhibit the excessive thorns.

However, symptoms vary on different rose types and cultivars. For example, red shoots do not occur in some ornamental rose varieties, and multiflora roses do not exhibit the excessive thorns.

What causes rose rosette?

Researchers have suspected that mite damage, phytoplasma, or a virus causes rose rosette disease.

  • Eriophyid mites

Transmission experiments using eriophyid mites collected from asymptomatic roses did not result in appreciable rose rosette symptoms (Armine et al,1988), making it unlikely that the eriophyid mite’s feeding causes the damage all by itself.

  • Phytoplasma

Phytoplasma (a specialized group of bacteria that infect plants) has long been considered a major candidate for the cause of the disease. Research articles from Poland (Kaminska et al, 2001), India (Chaturvedi et al, 2009), and China (Gao et al, 2008) demonstrated the presence of a phytoplasma (from the aster yellows family) causing rose rosette-like symptoms But, there are no reports of phytoplasmas in symptomatic roses in the United States. In an experiment where symptomatic plants were treated with antibiotics rose rosette symptoms persisted (Epstein and Hill,1995). Antibiotics should have killed or suppressed the phytoplasma

  • Virus

In 2011, a research group from the University of Arkansas detected a new virus, an Emaravirus negative strand RNA virus), in symptomatic roses. The virus occurred in 84 out of 84 symptomatic plants (Laney et al, 2011). This study also resulted in a genetic test to detect the virus. However, the procedure can be tedious.

Several diagnostic clinics, including the Texas Plant Disease Diagnostic Lab, are testing a modified,easier-to-use detection method. The Oklahoma Plant Disease and Insect Lab and the Texas Plant Disease Diagnostic Lab are two National Plant Diagnostic Network-affiliated labs that can test for the rose rosette virus using PCR methods.

What is so bad about a virus?

There is no effective way to treat a virus on an infected plant because the virus may be systemic (spread throughout the plant) and not a localized infection. When symptoms occur on only part of the plant, the disease may be localized, or it may be systemic but asymptomatic on other parts of the plant.

Pruning the infected part may eliminate the pathogen if the infection is localized, but, if systemic,the infection will persist. Mites carrying the virus can continue feeding on all parts of the rose and carry the virus to uninfected rose tissues.

What do studies show about how rose rosette disease is transmitted?

  • Grafting experiments (Thomas and Scott,1953; Epstein and Hill, 1995; Armine et al., 1988).

Grafting experiments on many different roses did not always result in transferring the rose rosette symptoms. Species and plant tissue age may have some influence; disease transmission was more efficient on rapidly growing tissue.

  • Eriophyid mite, Phyllocoptes fructiphilus (Allington et al. 1968, Armine et al, 1988).

To test the mites’ ability to transmit the disease, researchers took mites from infected, symptomatic plants and introduced them onto healthy plants.Although the disease was not always transmitted, the results suggest that the eriophyid mites can effectively transmit the disease for about 10 days. Experiments using eriophyid mites harvested from healthy plants and transferred to healthy plants did not result in rose rosette symptoms, suggesting that mite damage alone does not cause the symptoms.

  • Mechanical transmission experiments

To find out whether pruning practices might transmit the disease, leaf sap and juice, made by grinding infected plant parts, were rubbed on the leaves of healthy plants. This did not result in rose rosette symptoms (Allington et al, 1968).

Other experiments using contaminated razor blades to wound healthy plants also did not result in rose rosette symptoms. Stab inoculation, using a contaminated needle to wound healthy plants, resulted in rose rosette symptoms in two out of 120 tries (Epstein and Hill, 1995), showing that mechanical transmission is possible but highly unlikely.

How does the mite spread?

If plant parts are touching, it is possible that the mites could walk from one plant to the next. Movement for longer distances is thought to occur passively by wind (Keifer, 1975; Epstein et al., 1997) or by piggybacking on other insects (Shvanderov, 1975).

Do we know conclusively that the eriophyid mite is transmitting the rose rosette virus?

No published study clearly demonstrates that the eriophyid mite (Phyllocoptes fructiphilus) actually carries the rose rosette virus. Evidence from mite transmission studies suggests that the eriophyid mites are carrying and transmitting some disease-causing agent from the diseased plant.

Can the virus move through root grafts?

The more apt question is whether adjacent roses will graft their roots together. Many have said that this is unlikely, but Golino (2005) demonstrated possible root grafting by using a herbicide on a plant and observing the mortality of the adjacent roses. An experiment where researchers grafted pieces of roots from an infected plant onto a healthy rose resulted in rose rosette symptoms on the new plant, suggesting that root tissue can harbor the virus (Armine et al,1988).

If the virus is systemic and can get into the roots, it may be able to move to adjacent plants or new plants through the root graft. This theory has not been scientifically confirmed.

Why can’t I leave it alone and see if it recovers?

Sometimes rose rosette disease does not kill the rose but stunts it. Although it may recover on its own,it is highly unlikely, and the infected rose can serve as a virus reservoir. Theoretically, eriophyid mites can transmit the virus from a diseased plant to other roses.

How is this disease currently identified and/or confirmed?

The following methods are used to diagnose rose rosette disease:

  • Field identification based on symptoms (The reliability of symptoms is an issue since herbicide damage, insect damage, and nonbiological environmental conditions—such as wind, temperature, and sun—can mimic rose rosette symptoms.)
  • Detection of eriophyid mites along with disease symptoms
  • Electron microscopy to identify virus-like particles and soluble, membrane-bound particles(Rohozinski et al, 2001; Ahn et al, 1996; Silvestro and Chapman, 2004)
  • PCR analysis using molecular methods to detect the virus (see more below)

Are my roses “clean” if the genetic detection test is negative?

Not necessarily. The genetic test detects the presence of the virus on the sample. Typically, even though symptomatic plant tissue is usually used for the test, only a small portion of the plant is sampled. The sample does not show the extent that the virus is distributed throughout the plant. The sample may contain no viruses or viruses below the detection limit of the test. If infection is suspected, additional sampling and continued monitoring for symptoms and mites is advised.

What is the best way to deal with rose rosette disease?

Based on the current information about the disease and its presumed vector, the best management practices are:

  • Remove confirmed and/or symptomatic plants quickly.
  • Treat nearby plants with miticide to reduce the probability of disease transmission by eriophyid mites. But, this will not stop the virus if it is already in the plant.
  • Monitor symptoms weekly and act quickly when and if symptoms occur.
  • If desiring to replant with roses, remove all diseased plant roots from the soil before replanting
  • in the same area. This is a prudent precaution even though it is unlikely the virus spreads this way.

Conners I. L. 1941. Twentieth Annual Report of the Canadian Plant Disease Survey 1940. Domain of Canada Department of Agriculture Science Service, Division of Botany and Plant Pathology,Ottawa.

Epstein A. H. and Hill J. H. 1995. “The Biology of Rose Rosette Disease: A Mite-Associated Disease of Uncertain Aetiology.” Journal of Phytopathology 143:353–360.

Gao, R., Zhang, G. M., Lan, Y. F., Zhu, T. S., Yu, X. Q.,

Zhu, X. P., and Li, X. D. 2008. “Molecular Characterization of Phytoplasma Associated with Rose Witches’-Broom in China.” Journal of Phytopathology 156:93–98.

Kamińska, M., Podwyszyńska, M., and Śliwa, H. 2005. “Phytoplasma Detection in Rose Shoots Propagated in Vitro.” Acta Societatis Botanicorum Poloniae 74:181–186.

Rohozinski J., Epstein A. H., and Hill J. H. 2001. “Probable Mechanical Transmission of a Virus-Like Agent from Rose Rosette Disease-Infect- ed Multiflora Rose to Nicotiana Species.” Ann.

Appl. Biol. 138, 181–186.

Silvestro, S. R. and Chapman, G. B. 2004. “A Transmission Electron Microscope Study of ‘New Dawn’ Climber Rose (Rosa wichuraina x safrano) Exhibiting Rose Rosette Disease.” Plant Cell Rep. 23:345–351.

Thomas H. E. and Scott C. E. 1953. “Rosette of Rose.”Phytopathology 43:218–219.

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common name: eriophyid mite vector of Rose Rosette Disease (RRD)
scientific name: Phyllocoptes fructiphilus Keifer (Arachnida: Acari: Eriophyidae)

Phyllocoptes fructiphilus Keifer is a tiny eriophyid mite associated with most rose species and cultivars, especially in the eastern half of the USA. Most significantly, this mite is the vector of a devastating viral disease of roses called Rose Rosette Disease (RRD). This virus is a negative-strand RNA virus in the Emaravirus genus, which includes fig mosaic virus, raspberry leaf blotch virus, pigeonpea sterility mosaic virus and High Plains disease of maize and wheat, all of which are transmitted by other eriophyid mite species. The genome of this virus has been partially sequenced, which may allow geneticists to develop cultivars of roses that are resistant to RRD. The disease diagnosis can be confirmed with a molecular test called the polymerase chain reaction (PCR).

Figure 1. Phyllocoptes fructiphilus Keifer is a tiny eriophyid mite and cannot be seen without magnification. Like all eriophyid mites, it has only two pairs of legs at the anterior of its worm-like body. Photograph by USDA, Agricultural Research Service.

Rose Rosette Disease causes red coloration of new growth, excessive thorniness, elongated shoots, deformed blooms, witches broom of shoots (Fig. 2) and, ultimately, death of the plant. Rose Rosette Disease does not appear to be transmitted mechanically, although disinfesting all tools used on infected roses may be a useful precautionary effort. The virus does not survive well in soil, but the virus may survive in rose roots in the soil, so all roots should be removed from the soil when infected roses are removed. The disease somewhat resembles damage caused by herbicides, so diagnosis by PCR for the virus or by presence of the mites is helpful in discriminating between herbicide damage and RRD.

Figure 2. Feeding by the mite Phyllocoptes fructiphilus results in transfer of the virus to roses. Mites prefer to feed on tender new growth, and the virus modifies plant development to produce red foliage and stems, excessive thorniness, witches broom of shoots, and, ultimately, death. The mites are typically found in the apex of the rose shoots, where they feed and reproduce. Photograph by USDA, Agricultural Research Service.

Distribution (Back to Top)

Although Keifer described finding Phyllocoptes fructiphilus on Rosa californica in California in 1940, it is not found on commercially produced roses grown in the southern San Joaquin Valley at present. Whether this is due to the pesticides applied to these roses or to climatic conditions that result in low relative humidity is unknown. However, Phyllocoptes fructiphilus can be found on roses in the eastern half of the USA and it, and the disease it transmits, appear to be spreading into the New England states. As of 2013, this mite is not known to occur in Florida or the southern half of other Gulf States. It is interesting that the mite and the disease are not found on cultivated roses grown in large-scale nurseries in dry areas of California and Arizona, despite having been first identified on roses in California. Thus, it is not entirely certain what the native range or native host of the mite may be. Most assume that Phyllocoptes fructiphilus is native to North America on native rose species and has adapted to multiflora roses and cultivated roses.

Phillocoptes fructiphilus has become very abundant on multiflora roses (Rosa multiflora), which are introduced noxious weeds, especially in many states in the eastern half of the USA. Multiflora roses were introduced into the USA from Asia about 200 years ago, so the question arises as to whether the mite actually came from Asia with multiflora roses. The mite and the disease are not known to occur outside the USA, but this could be due to a lack of economic impact in Asia. Lack of knowledge about a tiny mite is not unusual when it is biologically controlled in its area of origin.

This mite can be spread by the wind and by contaminated clothing and equipment. It also is possible that it can disperse through phoresy (attaching itself to insects). As a result, the distribution of the mite and RRD is expanding.

Figure 3. Multiflora rose, Rosa multiflora,is a noxious weed in many states and the mite and RRD have been suggested as biological control agents for this weed. Unfortunately, the mite also attacks ornamental roses so it is no longer considered a potential multiflora weed control agent. Photograph by James H. Miller, USDA Forest Service, Bugwood.org.

Figure 4. Distribution of multiflora roses, Rosa multiflora, in the USA. Map by USDA.

Biology (Back to Top)

Phyllocoptes fructiphilus is 140-170 microns in length and 43 microns wide, so it is hard to see unless growing shoot tips and bud scales are examined under magnification. It is amber to light yellow in color and has no accepted common name.

Phyllocoptes fructiphilus has multiple generations a year. Mated adult females (deutogynes) overwinter under bark, old bud scales, and on living rose tissues. The overwintering females move onto developing shoots to deposit eggs, producing about one egg per day for about 30 days. The eggs hatch in 3 to 4 days and each protonymph and deutonymph requires about 2 days to develop. As a result, an egg can develop to adulthood in about one week, depending on the temperature. Both males and summer (protogyne) females are produced by arrhenotoky (females are diploid and males are haploid and produced from unfertilized eggs). This means that an unfertilized female can deposit a haploid (male) egg and become inseminated by her male offspring after he becomes an adult. Males deposit spermatophores on the substrate and females take up the spermatophores into their genital opening to fertilize eggs (that become daughters). A mated female may produce both fertilized (female) eggs and unfertilized haploid eggs that become males. Multiple generations develop until the weather turns cold in the fall. In the fall, deutogyne females are produced that enter their overwintering sites.

Phyllocoptes fructiphilus may be sensitive to low relative humidity, with periods of drought associated with low population densities. Very high densities of mites are found on plants with symptoms of RRD, suggesting that the virus-infected rose plant is more suitable for mites because infected roses have more apical shoots with tender new growth, which is where these mites thrive.

Hosts (Back to Top)

Phyllocoptes fructiphilus appears to survive on a wide array of Rosa species and cultivars, including the non-native multiflora rose. There are anecdotal accounts that some cultivars are possibly resistant to the mite (or the virus), but there are no clearly resistant cultivated rose cultivars known at present. Breeders are attempting to identify possible resistance genes in order to develop resistant cultivars to either the mite or the virus. Breeding for RRD resistance is important for the future of rose culture in the USA and, possibly, the world’s rose culture.

Economic Importance (Back to Top)

Roses are valued for their beauty and scent and the rose is the national flower of the USA. Cut roses, rose bushes and rose oil are commercially valuable. Commercial rose producers plant tens of thousands of roses each year. Cultivation is highly labor-intensive due to the fact that pruning, spraying, fertilizing, and harvesting are done by hand. Rose production employs workers in farming, transportation, marketing, and delivery to wholesale and retail markets. Internationally, the cut floral industry, of which roses account for two-thirds of all such plants, exceeds $40 billion dollars per year. There is no guarantee that RRD and the mite vector can be contained in the USA due to the export of roses around the world, so the economic impact of this mite and the disease it transmits could increase.

Figure 5. Cultivars of roses are grown for their beauty and scent. Thousands of different rose cultivars have been developed through breeding. Photographs by USDA, Agricultural Research Service.

Figure 6. Cultivars of roses are grown for their beauty and scent. Thousands of different rose cultivars have been developed through breeding. Photograph by USDA, Agricultural Research Service.

Management (Back to Top)

Phyllocoptes fructiphilus should be managed because it is the vector of RRD. Guidelines provided by Star Roses and Plants/Conard-Pyle for managing the mite and the disease include: 1) Once a rose is identified as RRD-infected, the plant should be removed immediately by burning or disposing of it in a sealed plastic bag. Do not add it to your mulch pile or compost bin. 2) Because the disease can possibly spread from RRD-infected rose roots to a neighboring rose plant, removal of the rose with RRD should include removal of its roots, as well. 3) Pruning of roses may eliminate mites and eggs, which are found in the crevices of cane petioles and in new growth. 4) Remove any multiflora roses in the vicinity of your cultivated roses by using herbicides, repeated cutting or mowing 3-6 times a growing season for 2-4 years, or by application of a systemic herbicide to cut stumps or regrowth. However, seeds of multiflora roses are numerous and long lived in the soil, so vigilance is required to eliminate multiflora roses in the vicinity of cultivated roses. Robins, mockingbirds, starlings, red-winged blackbirds, and other species feed heavily on multiflora rose hips in fall and winter, and seeds pass rapidly through their digestive tracts and remain intact, resulting in increases in the germination rate, while the bird feces provide fertilizer to seedlings.

It is unclear which pesticides are effective to manage this mite. Because the mite is “hidden” in the buds on the growing tips, coverage is difficult to achieve. However, it is known there are natural enemies (predatory mites, fungi) of many eriophyid species, so the use of “soft pesticides”, such as light horticultural oils, sulfur, soaps, etc., may preserve the naturally occurring natural enemies.

The use of augmentative biological control, in which releases of specific natural enemies are made to control the pest, has not been investigated at this time. It is unknown which predatory species might be effective, or at what application rate. Several predatory mites (phytoseiids) are known to be effective natural enemies of eriophyid mites in orchards and vineyards, so it is likely that naturally occurring predatory mites (Acari: Phytoseiidae) could be effective in suppressing Phyllocoptes fructiphilus. However, these predatory mites may be susceptible to pesticides used to control other pests and diseases of roses, so studies are needed to confirm their effects on predatory mites. Because even a single mite could, in theory, transmit the virus, biological control by itself can only reduce the pest population and thus, reduce the incidence of RRD. Ultimately, the development of rose cultivars that are resistant to either the mite or the virus (or both) is likely to provide a more-effective control of RRD in cultivated roses.

Selection of rose cultivars using traditional breeding methods may be laborious and slow; it could take years to identify resistant/tolerant sources for breeding to commercial cultivars with desirable ornamental traits. The development of genetically modified horticultural roses using recombinant DNA methods might provide a more rapid resistance to the mite or RRD and the public may accept such genetically modified roses because roses typically are not used as food.

Reliance on host-plant resistance, once developed, can be risky because the mite and the virus could become resistant to the host-plant resistance. Thus, a multi-tactic approach will still be needed to manage RRD vectored by Phyllocoptes fructiphilus. This should include eradicating multiflora roses within 300 feet of cultivated roses, removing infected cultivated roses and their roots, preservation of natural enemies of the mite by use of “soft” pesticides to control the mite and other rose pests and diseases. Likewise, reliance on chemical control as the primary tool is risky; at least nine other species of eriophyid mites have developed resistance to pesticides. Eriophyid mites are so tiny that they are difficult to detect by plant inspectors using hand lenses. As a result, at least 80 species of eriophyids have become invasive alien species around the world and this mite (and the virus it transmits) could become a pest in other rose-growing regions of the world.

Selected References (Back to Top)

  • Amrine JW, Hindal DF. 1988. Rose rosette, a fatal disease of multiflora rose. West Virginia Agricultural Experiment Station Circular 147: 1-4.
  • Amrine JW. 1996. Phyllocoptes fructiphilus and biological control of multiflora rose. In: Lindquist EE, Sabelis MW, Bruin J (Eds.) Eriophyoid Mites-Their Biology, Natural Enemies and Control. Elsevier, Amsterdam, pp. 741-749.
  • Amrine JW. 2002. Multiflora rose. In: Van Driesche et al. Biological Control of Invasive Plants in the Eastern United States. USDA Forest Service Publication FHTET-2002-04, 413 p.
  • Amrine JW, Hindal DF, Williams R, Appel J, Stasny T, Kassar A. 1990. Rose rosette as a biocontrol of multiflora rose. Proceedings of the Southouthern Weed Science Society 43: 316-319.
  • Comard-Pyle. 2013. Rose rosette disease. Prevention Guide. Star Roses and Plants/Conard-Pyle.
  • Doudrick RL, Enns WR, Brown MF, Millikan DF. 1986. Characteristics and role of the mite, Phyllocoptes fructiphilus (Acari, Eriophyidae) in the etiology of rose rosette. Entomological News 97: 163-172.
  • Epstein AH, Hill JH. 1999. Status of rose rosette disease as a biological control for multiflora rose. Plant Disease 83: 92-101.
  • Hinda DF, Wong SM. 1988. Potential biocontrol of multiflora rose, Rosa multiflora. Weed Technology 2: 122-131.
  • Jesse LC, Moloney KA, Obrycki JJ. 2006. Abundance of arthropods on the branch tips of the invasive plant, Rosa multiflora (Rosaceae). Weed Biology and Management 6: 204-211.
  • Keifer HH. 1940. Eriophyid studies VIII. Bull. Dept. Agric. State of Calif. Vol. XXIX, No. 1.
  • Kostiainen TS, Hoy MA. (1994). The Phytoseiidae As Biological Control Agents of Pest Mites and Insects. A Bibliography (1960-1994). University of Florida Institute of Food and Agricultural Sciences Monograph 17, Gainesville, FL.
  • Laney AG, Keller KE, Martin RR, Tzanetakis IE. 2011. A discovery 70 years in the making: characterization of the rose rosette virus. Journal of General Virology 92: 1727-1732.
  • Mielke-Ehret N, Muhlbach HP. 2012. Emaravirus: a novel genus of multipartite, negative strand RNA plant viruses. Viruses 4: 1515-1536.
  • Navia D, Ochoa R, Welbourn C, Ferragut F. 2010. Adventive eriophyoid mites: a global review of their impact, pathways, prevention and challenges. Experimental and Applied Acarology 51: 225-255.

Frequently Asked Question About Rose Rosette Virus

Distorted flower buds
Millie Davenport, ©2013 HGIC, Clemson Extension

Rose rosette virus (RRV) has been making an unwelcome appearance in landscapes around the Carolinas. Rose rosette disease was first detected in California, Wyoming, and Manitoba Canada in 1941. By 1994 it had spread to Tennessee and has since made its way to the Carolinas. The pathogen that causes this disease was just recently identified as a virus. It most likely spread across the United States through wild rose populations, such as Rosa multiflora. Multiflora roses are very susceptible to this disease and are also considered invasive plants in our region. The population of wild multiflora roses in the Carolinas has helped spread this virus, which is particularly lethal to multiflora roses, and is potentially lethal to other rose species and cultivars.

How is Rose rosette virus spread?

Other organisms called vectors often spread viruses. The primary vector of this virus is an eriophyid mite. Eriophyid mites can be found on tender new growth of buds and between stem and leaf petioles. Mites carrying the virus pass it from plant to plant as they feed on the plant sap of tender stems. Humans can also vector the virus through grafting and pruning. The virus does not stay in one place on the plant. Once a plant is infected the virus moves throughout the entire plant, including the roots and shoots.

Distorted leaves
Millie Davenport, ©2013 HGIC, Clemson Extension

How did eriophyid mites get to my roses?

Eriophyid mites have 4 legs and are yellow to brown in color. These mites are not visible to the naked eye; they are less than 1/200 inch long, which is about 3 to 4 times smaller than an average spider mite. These small mites move easily with wind currents. Eriophyid mites present on nearby populations of infected wild multiflora roses can easily travel to your landscape. Also, infested plants could be unknowingly purchased and introduced to the landscape.

How do you recognize rose rosette disease in the landscape?

Early detection of the disease is crucial to keep other nearby roses healthy. However, early detection can be difficult because symptoms such as witch’s brooms and misshapen leaves mimic damage typically caused by herbicides. Roses should be inspected for symptoms in the spring when new growth starts to appear. The appearance of these symptoms will increase as the growing seasons progresses. Symptoms may vary by rose species or cultivar. Some common symptoms of rose rosette disease are listed below.

Distorted flower petals
Millie Davenport, ©2013 HGIC, Clemson Extension

  • Shoots and foliage have an abnormal red color
  • Stems appear thick and succulent
  • Rapidly elongating shoots
  • Shoots with shortened internodes
  • Stems with an overabundance of pliable thorns
  • New growth may have many branches that create a witch’s broom (similar to glyphosate injury)
  • Distorted or dwarfed leaves (similar to 2.4-D injury)
  • Deformed buds and flowers
  • Abnormal flower color
  • Lack of winter hardiness
  • Spiral cane growth

Why is rose rosette disease showing up on disease-resistant roses such as Knockout roses?

The Knockout rose has become a staple in the landscape. When introduced to the market in 2000 it was named the All-American Rose Selection Winner. They were marketed as low-maintenance, drought tolerant, self-cleaning roses that were resistant to powdery mildew and black spot. It is no surprise that this new rose took the market by storm, with record-breaking sales for a new rose and becoming the most widely sold rose in North America. Since then, Knockout roses have been used in mass plantings in multiple landscapes. Having many plants of one variety planted close together makes it easy for insects and diseases to spread, and that is particularly true for this disease.

Shoot and foliage with abnormal red color.
Millie Davenport, ©2013 HGIC, Clemson Extension

How do I prevent this virus from infecting my roses?

It is best to start by purchasing disease free plant material. When visiting the nursery inspect plant material and avoid buying roses that show symptoms of this virus. When planting new roses in the landscape, leave enough space for plants to mature without overlapping stems or leaves of neighboring roses. This extra space will help prevent mites from crawling from one plant to the next. Next, remove wild multiflora roses that exist within 100 yards of the landscape. If this is not possible consider using a different plant species. The use of pesticides as a preventative is not a practical solution, and most miticides are not effective against eriophyid mites.

What if I don’t know what multiflora roses look like?

Multiflora roses are often found growing wild on roadsides and pastures. They have an erect habit with arching branches from 3 to 10 feet long. This rose produces fragrant, 1-inch white to pink flowers with 5 petals from April to June in the Carolinas. To control multiflora roses in the landscape, cut them to the ground in late summer and spray cut stem ends with glyphosate. If the plant re-sprouts, spray tender growth with glyphosate. Examples of glyphosate products are Roundup Original, Eraser Systemic Weed & Grass Killer, Quick Kill Grass & Weed Killer, Bonide Kleenup Grass & Weed Killer, Hi-Yield Super Concentrate Killzall Weed & Grass, Maxide Super Concentrate 41% Weed & Grass Killer and Southern States Grass & Weed Killer Concentrate.

What do I do if my roses are already showing signs of infection?

Stem with overabundance of pliable thorns
Millie Davenport, ©2013 HGIC, Clemson Extension

Unfortunately infected plants are not curable. So, it is best to remove any diseased plants from the landscape. This virus is systemic and will move throughout all parts of the plant including the roots, and cannot be pruned out of the plant. Pruners used on infected roses should be disinfected before use on other roses to prevent spreading the virus. Remove and bag any plant material (including roots) in the landscape to prevent spreading it to healthy roses. Be aware that roots left in the ground are still infected and could re-sprout. If this happens, cut and remove the shoots.

Will my plants live? If not, how long will it be before they die?

Plants infected with the Rose rosette virus cannot be cured. These infected plants should be removed. If diseased plants are left in the landscape they will most likely die in a couple of years, all the while allowing the virus to spread to other nearby roses.

Are my other plant species susceptible to this virus?

The good news is that the rose rosette virus is host specific and only roses are susceptible to this disease. The bad news is that most rose species and cultivars are considered susceptible to this virus.

How long will it be before I can replant the area?

The area can be replanted with a non-rose species immediately. It is not recommended to plant rose species in this area until all remaining roots from the diseased roses are removed.

By David Kuack|February 4, 2013

The recent release of new hybrid landscape roses, including the Flower Carpet and Knock Out series, has raised interest in these ornamental plants for growers, landscapers and homeowners. According to the USDA-National Agricultural Statistics Service’s Nursery Crops 2006 Summary, deciduous shrubs, including roses, accounted for $648 million in gross sales.

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Deciduous shrubs were the second largest contributor to sales — behind broadleaf evergreens with sales of $839 million — and accounted for 14 percent of the nursery sales total. But as breeders continue to develop rose varieties that are more disease resistant and easier to grow, one disease continues to elude their efforts to hybridize resistant varieties: rose rosette disease.

Symptoms Vary Based On Rose Species, Cultivar

Although symptoms of this disease were seen as early as the 1940s, the cause of rose rosette was not reported until 2011. Researchers at the University of Arkansas identified a negative-sense RNA virus that is strongly associated with rose rosette and developed detection tests for the virus. They found it in more than 80 plants, which showed disease symptoms. The virus was detected in all diseased plants but not in healthy-looking plants.

Plants infected by the virus can show a variety of symptoms. The severity of the symptoms differs with rose species and cultivar. The most severe symptoms are witches’ broom, lateral shoot elongation, bright-red coloration on leaves and malformation of flowers and leaves.

Growers should not assume the witches’ broom symptom is an indicator of rose rosette. This symptom can also be associated with certain types of herbicide damage. Fall applications of the herbicide glyphosate that contact the green tissue of rose plants can result in translocation of chemical into the buds. However, herbicide damage symptoms don’t become evident on the plants until the buds expand the following spring. Witches’ brooms symptoms caused by glyphosate injury usually appear as yellow, narrow leaves on clusters of shoots.

Flowers infected with rose rosette may produce fewer petals, and their color may be abnormal, such as a mottling coloration pattern. Flower buds may abort, be deformed or develop with leaf-like tissue. Infected rose canes may display excessive growth with red or green pliable thorns that eventually harden. Diseased canes may develop slowly, grow in a spiral pattern and be thicker than the parent canes from which they developed. Plants with the disease usually die in two to five years depending on the rose species.

A plant may display few of the symptoms, especially in the early stages of the disease. As the symptoms become severe and recognizable, there is an increased likelihood the disease will spread to nearby rose plants.

How The Disease Spreads

The virus associated with rose rosette disease is vectored by a small eriophyid mite (Phyllocoptes fructiphilus). The mite is transported over long distances by wind currents, and the virus can also be transmitted during propagation by grafting. Once a plant is infected with the virus, it becomes systemic. Although the virus is not soil-borne, it can persist in root pieces that remain in the soil. The wild rose species Rosa multiflora is highly susceptible to the disease.

Multiflora rose has become a primary host and source of the virus. Originally, it was introduced into the U.S. in the 1860s as a rootstock for ornamental roses. During the 1930s through the 1960s, the U.S. Soil Conservation Service recommended planting multiflora rose for soil erosion control, wildlife conservation and strip mine reclamation. It was also recommended as a living fence for cattle and a highway crash barrier.

Multiflora rose produces millions of seeds per plant and can also propagate itself vegetatively. It spreads quickly and has become so well established it is considered an invasive plant or noxious weed in some states, including Iowa, Ohio, West Virginia and New Jersey.

Increased reports of rose rosette disease have occurred within the last two years, says Michael Dobres, managing director of NovaFlora LLC, the research division of Star Roses and Plants/Conard-Pyle Co. The disease is not as prevalent beyond the Rocky Mountains because there are less plantings of R. multiflora than in the Midwest and on the East Coast.

“There has been a steady west to east movement of the disease over the last decade,” Dobres says. “If rose rosette continues to become more prevalent, we would hope that R. multiflora would be designated as an invasive plant by more states. Multiflora is around because of its extremely high seed set and because it is invasive. As an industry we should try to discourage the use of multiflora as much as possible.”

The good news is some wild rose species have shown resistance to the disease.

“There are about a half dozen rose species native to the U.S. that appear to have resistance to rose rosette,” Dobres says. “We’re actually looking at these roses at Star Roses and Plants. We’re looking at some of the genes from these roses through cross-pollination into some commercial hybrid roses. From the breeding standpoint, we are looking at disease-resistant wild varieties to develop ornamental hybrids. But developing disease-resistant hybrids is something for the future and is expected to take quite a while.”

Controlling Rose Rosette

Currently there are no chemical controls for the virus that causes rose rosette disease. Carlos Bográn, manager of technical services at OHP Inc., says growers need to develop a relationship with their rose propagators to ensure they are receiving disease-free roses.

“There has to be an agreement between the grower and propagator,” Bográn says. “They have to be partners in minimizing the spread of rose rosette disease. If a grower is not sure whether his plants are infected with the disease, he has to have the plants’ virus indexed like other virus diseases, such as hosta virus X.”

One of the most effective ways of controlling the spread of the disease is to eliminate multiflora rose from the immediate vicinity through cutback and the application of herbicides, Dobres says.

“We have prepared a Rose Rosette Disease Guide that lists various herbicides effective in controlling multiflora,” Dobres says. “The ability to use those herbicides may vary by state, and eliminating multiflora rose in every state is a nearly impossible task. We have to focus on eliminating it from areas surrounding landscape rose plantings and around grower production areas.”

The multiflora rose usually blooms during May and June. Plants produce fragrant, 1-inch diameter, white-to-pink flowers. Small, bright-red rose hips develop during the summer, become leathery and remain on the plant through the winter.

“Good cultural practices are essential and will go a long way in reducing the incidence of this disease,” Dobres says. “The most practical recommendation is for both growers and landscapers to do a heavy prune of dormant ornamental roses during late winter just before new growth appears. If growers and landscapers remove the upper portion of ornamental roses where eriophyid mites can be found in the leaf axils, it will significantly reduce the disease pressure on the plants.”

Controlling The Mites

Controlling the eriophyid mite that vectors rose rosette disease can be an effective deterrent in the spread of the disease, Bográn says.

“Growers don’t have to be concerned that this mite will attack and spread the disease to other ornamental plants,” he says. “They have to be concerned about roses, in particular multiflora.”

Three miticides (Avid, Akari and Judo) along with horticultural oil have been listed as controls in Conard-Pyle’s Rose Rosette Disease Guide.

“We advise growers who use these miticides to rotate between the three chemicals,” Dobres says. “It is important to rotate these miticides so that the mites don’t build up resistance. These are contact controls and it is important to use them in rotation.”

Bográn says growers should also consider testing Kontos, a systemic insecticide/miticide labeled for spider mites and other sucking insects, on greenhouse and nursery crops. It can be used as both a spray and drench application.

“The benefit of using a systemic is that it is active in feeding sites that may not be reached by a spray application,” Bográn says. “Also, since the chemical is systemic and is taken up through the plant roots, a drench provides longer residual activity than a spray application.”

Plants should be monitored on a weekly basis throughout the growing season, which is usually April through June, depending on where a grower is located. Ornamental roses showing symptoms of the disease should be removed and discarded by burning or placing plants in plastic bags.

“A grower should confirm that the symptoms have been caused by the disease and not herbicide damage,” Dobres says. “If a diseased plant is identified, it should be removed and destroyed, both in the production environment and in a landscape planting.”

David Kuack () is a freelance technical writer in Fort Worth, Texas. See all author stories here.

Rose rosette virus (rose rosette disease)

Resistance

R. multiflora is the species that appears to be most susceptible to RRD. However, many species and selections of cultivated roses are also highly susceptible, and no cultivars have been proven to be resistant. Although the native species Rosa setigera is reported to be resistant to the disease, one grower has reported increased susceptibility to powdery mildew on plants of R. setigera, which could indicate some level of infection by the RRD pathogen. The species Rosa bracteata (also called the McCartney rose), which exists as a weed in southern states, is susceptible to RRD but resistant to feeding by the mites that transmit the disease. It may be possible, through breeding techniques, to incorporate this mite resistance into cultivated roses in the future. In the meantime, it would be wise to assume that all cultivated roses are potentially susceptible to the disease.

Diagnostic procedures

Because symptoms of RRD can be confused with those of herbicide injury from glyphosate, it is important to obtain background information on the timing of disease development and the history of herbicide use near affected plants when trying to diagnose the disease by symptoms alone. One symptom that appears to be diagnostic for RRD, if present, is the presence of canes of large diameter emerging from canes of smaller diameter.

Laboratory tests for diagnosing RRD include demonstration of transmission of symptoms from affected stems grafted onto healthy plants, as well as use of molecular techniques for detection of the virus. It can take months to obtain results with the grafting technique, whereas use of reverse transcription and polymerase chain reaction can be done in a relatively short period of time. Refer to the article, How We Test for Rose Rosette in Oklahoma, by Jen Olson for details on extracting viral RNA, and performing reverse transcription and PCR for detecting RRV. Note that diversity among viral isolates could potentially cause a false negative result. If a symptomatic plant tests negative, it would be a good idea to re-test with a different set of primers.

Some have also used identification of the eriophyid mite vector as a means of diagnosis of RRD; however, presence of the mite does not confirm presence of the virus. Also, the mites are very small and may be difficult to find on the plant even if they are present.

Resources and References

Acknowledgments

  • National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of “Diagnostic Image Series Development for Supporting IPM in the Southern Region” (USDA-NIFA-RIPM-003351)

What to Look For

Symptoms

The symptoms of RRD are variable, depending on the cultivar of rose (Table 1). In the early stages, plants may develop elongated stems with reddened foliage, the latter characteristic being typical of new growth with many cultivars, but if this foliage does not gradually turn green, the plant is most likely infected (Figure 1). However, this reddening is not a consistent symptom. Elongated shoots may be engorged and pliable, with overabundant thorns (Figures 2 & 3).

Table 1: Typical RRD symptoms

Elongation and thickening of shoots/stems

Red leaf mottling (mosaic) that does not disappear as leaves mature

Leaf distortion

Excess thorns

Yellowing and stunting of plants

Witches’ brooms (rosettes)

Flower distortion, discoloration or blight

Branch/shoot dieback

Reduced winter hardiness

Increased susceptibility to other diseases

Figure 1: This shrub rose exhibits leaf distortion and discoloration typical of rose rosette disease
Figure 2: Stems affected by RRD may swell and grow excess thorns
Figure 3: Stems affected by RRD (left) may swell and grow excess thorns

Another common symptom of RRD is “witches’ brooms,” brush-like clusters of shoots and branches that originate at the same point. Such growths are also called “rosettes,” lending the name to the disease (Figure 4). The foliage within these rosettes may be stunted, distorted and mottled red or yellow. Witches’ brooms will spread randomly across the plant as the disease progresses. Flowers may be distorted or fail to open fullly (Figure 5). Severely infected plants may not produce flowers.

RRD will commonly cause defoliation and dieback, and in severe cases plants may die within 2-3 seasons. Infected plants have reduced winter hardiness, making them more susceptible to cold damage. Plants stressed by RRD are also more susceptible to other diseases such as black spot and powdery mildew.

Figure 4: ‘About Face’ Grandiflora Rose cultivar with witches’ brooms
Figure 5: Blooms may display discoloration, mottled color, or fail to open completely

Look-alike Injury

Many of these symptoms of RRD resemble herbicide drift injury, especially that of Glyphosate, the active ingredient in Round-up®. The commonly-used broadleaf herbicide 2, 4-D can also cause leaf distortion on roses. The only symptoms that may not be present with such poisoning are excessive thorniness and red pigmentation. Such herbicide injury symptoms should disappear in the following year unless the plants are re-injured by drift. Nutrient deficiency may also resemble RRD injury, but will typically affect the whole plant. Therefore, it is important to check for combinations of RRD symptoms over time.

Disease Cycle

RRD, formerly thought to be caused by aster yellows phytoplasma, which also causes witches’-broom-like growths on affected plants, is actually caused by a negative-sense RNA virus called Rose rosette virus, of the genus Emaravirus. The disease is transmitted by the eriophyid mite Phyllocoptes fructiphilus. It can also be transmitted via grafting, but is not sap-transmissible. The virus is not soil borne, but if infected root pieces remain in the soil after infected plants are removed, they could potentially infect newly-transplanted healthy plants.

Eriophyid mites are microscopic mites that are 3 to 4 times smaller than even an average spider mite. They are so small that they can be transported by wind. They transmit the disease by feeding on infected wild (such as multiflora rose) or cultivated rose plants and being transported via wind and/or clothing and tools of landscape workers to healthy plants, where they feed again and introduce the virus.

Once on a plant, the mite travels very little, and tends to hide out in buds, on open flowers and sepals, or at the base of shoots, leaf axils and in leaf scars during the winter. The virus makes its debut on emerging foliage in the spring, otherwise being inactive during winter months.

Figure 6: Multiflora rose (Rosa multiflora) is a landscape rose known to harbor RRD and/or eriophyid mites. It should be removed from any nearby cultivated rose plantings, and is considered an invasive species

Lewis Ginter Botanical Garden

Jul 5th, 2015

by Jonah Holland

Rose rosette disease — see the deformed leaves and buds? Also note the very red foliage.

Rose rosette disease is a funny thing. At first it doesn’t look like there’s a problem with your roses, it just looks like there is alot of new growth, and the foliage is more pliant, more red, and almost furry, instead of prickley. (Did you know that roses have prickles, not thorns? Botanically speaking, thorns are derived from shoots and therefore can only arise from a bud. Prickles are derived from the epidermis, a skin-like layer covering the surface of plants, and so can arise anywhere on a plant.) But it’s easy to notice soon enough that something isn’t right with your plant. The leaves become deformed, the new growth looks strange, mutant, — and like a “witch’s broom”(….not that I’ve ever seen a witch’s broom.) In fact, rose rosette disease is also call witches’-broom of rose. It is a virus spread by garden shears or chewing/sucking insects called eriophyid mites, that can travel on the wind. You can try to prevent it from spreading in your garden by using alcohol or Lysol wipes on your pruners and shears between plants. But, sometimes there’s nothing you can do to prevent it.

Senior horticulturist Elizabeth Fogel showing rose rosette disease on one branch. The branch in the background is still healthy, but it’s only a matter of time before the whole plant is infected.

Recently we had this virus appear on one of our old fashioned Victorian style roses in Grace Arents Garden, on a rose that was part of the original design from the Garden Club of Virginia restoration back in 1990. Our Rosa x ‘Ballerina’ will be replaced with an identical rose, as soon as we can find one. It has a matching sister on the other side of the arbor. Grace Arents Garden Senior Horticulturist Elizabeth Fogel says, “The best thing, if you’ve got other roses you want to protect is just to get ride of the rose as soon as you can. The bugs will bite into the plant and spread this to other plants.”
It’s important to remove the entire plant to avoid the spread of the disease to other plants, but keep in mind, sooner or later this disease will kill your rose bush anyway in 2 to 5 years. Do not compost this plant when you pull it out — throw it in trash so it doesn’t spread the disease to others.

Missouri Botanical Garden says our case of rose rosette disease fits the disease’s normal life cycle. “Transmission typically occurs between the months of May through mid-July. Symptoms from new infections usually start appearing in mid-July.” For more information, there are good resources and additional photos on their Rose Rosette webpage.

Fogel showing the super-prickley, red, pliable new growth of rose rosette disease.

Rose Rosette Disease—What Is It, and What Can You Do About It?

If you’ve been on some of the rose forums, attended rose talks, or even just talked roses with friends on Facebook, you’ve likely heard of rose rosette disease, or RRD. While it’s been around a while, I’ve noticed it’s starting to show up on the radar screen of more and more general gardeners. So I thought it’s time we talked about it.

First, what is it? It is a disease that is carried by a very specific spider mite, ‘Phyllocoptes fructiphilus’. An infected mite drifts on the wind, comes into your garden, lands on your roses, and then injects the disease into the rose when it starts to feed. Or a noninfected mite lands on a rose that already has it, picks it up, and then is blown by the wind to another rose, which it proceeds to infect.

You know you’ve got it when your roses start to throw off strange growth that is purplish in color and most noticeably has “foliage” in the shape of what is called “witches broom” (see photos). It actually looks a lot like Roundup damage.

An infected cane. Notice the strange witches-broom-like growth.
Photo/Illustration: Paul Zimmerman Roses Another view.
Photo/Illustration: Paul Zimmerman Roses

It is particularly lethal to the species R. multiflora and in fact has been mentioned as a potential biological control method for it. R. multiflora spreads like crazy, and in much of the eastern United States it’s classified as a noxious weed. In their attempt to control it, some government officials actually facilitated the spread of RRD by purposely infecting stands of multiflora. They claim there was no scientific proof RRD infected ornamental roses, the kind you and I grow in our garden.

Well, guess what? They were flat out wrong! RRD does affect ornamental roses, although some more than others. And that is enough about how it got here. Since this is a how-to article, we now want to answer the question: What the heck can you do about it?

First, let’s talk about what you can do to reduce the likelihood of it getting into your garden. Since it hits R. multiflora quickly, check in your area for stands of that species. R. multiflora only blooms in spring with smaller white flowers that have five or so petals each. That’s the easiest time to spot it. When it’s not in bloom, the foliage helps. It’s a shiny green, and the leaves are elongated. It’s usually thornless, which really helps. It’s a rambler and so throws off long canes. Dig it up and get rid of it. That’s your first step.

If RRD does happen to infect a rose in your garden, there is no known cure. However, I’ve noticed in dealing with it that there are steps I can take. The first one is understanding how it spreads in a rose. The mites land on the top of a rose cane, where the new tender foliage is. They inject RRD into that part of the rose, and from there it slowly travels down through the cane to the base and then up the other canes. The important word here is slowly.

I’ve noticed that the symptoms on the infected cane (the witches broom) often show up before the rest of the plant is infected. So the minute I see the witches broom, I follow that cane to the base of the plant and cut it off at the base. I put it in a garbage bag and get rid of it so I don’t accidentally shake any mites onto another rose. Eventually the cut-off cane is replaced by a new one, and it’s as if nothing ever happened.

However, if the disease appears to have spread into another section of the rose, you have no choice but to dig the entire rose up and either destroy it or get rid of it via the plastic garbage bag. I’ve lost a couple, and I know others who have lost more. But once they understood what was happening and how to deal with it, the incidents became less.

So does this mean you should simply stop growing roses? Of course not! RRD is a bummer when you first get it, but by knowing how to deal with it, you can reduce it to another part of normal garden maintenance. Just keep an eye out for it, and act quickly.

For further reading, check out Ann Peck’s amazing website on RRD.

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What Is Rose Rosette Disease: Control Of Rose Rosette And Witches Broom In Roses

By Stan V. Griep
American Rose Society Consulting Master Rosarian – Rocky Mountain District

Rose Rosette disease, also known as witches broom in roses, is truly a heartbreaker for the rose loving gardener. There is no known cure for it, thus, once a rose bush contracts the disease, which is actually a virus, it is best to remove and destroy the bush. So what does Rose Rosette disease look like? Keep reading for information on how to treat witches broom in roses.

What is Rose Rosette Disease?

Exactly what is Rose Rosette disease and what does Rose Rosette disease look like? Rose Rosette disease is a virus. The effect it has upon the foliage brings about its other name of witches broom. The disease causes vigorous growth in the cane or canes infected by the virus. The foliage becomes distorted and frazzled looking, along with being a deep red to almost purple in color and changing to a brighter more distinct red.

The new leaf buds fail to open and look a bit like rosettes, thus the name Rose Rosette. The disease is fatal to the bush and the longer one leaves it in the rose bed, the more likely it is that other rose bushes in the bed will contract the same virus/disease.

Below is a list of some of symptoms to look for:

  • Stem bunching or clustering, witches broom appearance
  • Elongated and/or thickened canes
  • Bright red leaves** and stems
  • Excessive thorniness, small red or brown colored thorns
  • Distorted or aborted blooms
  • Under-developed or narrow leaves
  • Perhaps some distorted canes
  • Dead or dying canes, yellow or brown foliage
  • The appearance of dwarfed or stunted growth
  • A combination of the above

**Note: Deep red colored leaves may be totally normal, as the new growth on many rose bushes starts out with a deep red coloration and then turns to green. The difference is that the virus infected foliage keeps its color and can also become mottled, along with vigorous unusual growth.

What Causes Witches Broom in Roses?

The virus is believed to be spread by tiny mites that can carry the nasty disease from bush to bush, infecting many bushes and covering much territory. The mite is named Phyllocoptes fructiphilus and the type of mite is called an eriophyid mite (wooly mite). They are not like the spider mite most of us are familiar with, as they are far smaller.

Miticides used against the spider mite do not appear to be effective against this tiny wooly mite. The virus does not appear to be spread by way of dirty pruners either, but only by the tiny mites.

Research indicates that the virus was first discovered in wild roses growing in the mountains of Wyoming and California in 1930. Since then it has been a case for much study at plant disease diagnostic labs. The virus has recently been placed into a group known as Emaravirus, the genus created to accommodate a virus with four ssRNA, negative sense RNA components. I won’t go further into this here, but look up Emaravirus online for further and interesting study.

Control of Rose Rosette

The highly disease resistant knockout roses seemed to be an answer for disease problems with roses. Unfortunately, even the knockout rose bushes have proven to be susceptible to the nasty Rose Rosette disease. First detected in the knockout roses in 2009 in Kentucky, the disease has continued to spread in this line of rose bushes.

Due to the huge popularity of the knockout roses and the resulting mass production of them, the disease may well have found its weak link to spreading within them, as the disease is readily spread through the grafting process. Again, the virus does not appear to be able to spread by pruners that have been used to prune an infected bush and not cleaned before pruning another bush. This is not to say that one does not need to clean their pruners, as it is highly recommended to do so due to the spread of other viruses and diseases in such a manner.

How to Treat Witches Broom on Roses

The best thing we can do is to learn the symptoms of the disease and not buy rose bushes that have the symptoms. If we see such symptoms on rose bushes at a particular garden center or nursery, it is best to inform the proprietor of our findings in a discreet manner.

Some herbicide sprays that have drifted over onto rosebush foliage can cause foliage distortion that looks very much like Rose Rosette, having the witches broom appearance and the same coloration to the foliage. The tell-tale difference is that the growth rate of the sprayed foliage and canes will not be extremely vigorous as the truly infected bush will be.

Again, the best thing to do when you are certain a rose bush has the Rose Rosette virus is to remove the bush and destroy it along with the soil immediately around the infected bush, which could harbor or allow overwintering of the mites. Do not add any of the infected plant materials to your compost pile! Be vigilant for this disease and act quickly if observed in your gardens.

Rose Rosette Virus

This is a curated page. Report corrections to Microbewiki.

Figure 1: Witches’-broom caused by rose rosette disease on a shrub rose (Rosa ‘Baiore’ POLAR JOY). Image from the Missouri Botanical Garden

Introduction

By Jacob Scharfetter

Rose rosette virus (RRV), also known as Rose rosette disease (RRD), is a viral plant pathogen The symptoms of Rose rosette virus (RRV) were first recognized and recorded in Canada 77 years ago. Since then, RRV has become one of the most destructive diseases of commercial roses. The plant pathogen RRV has only been found to affect the genus Rosa. However, within the genus Rosa, most species are susceptible to RRV, making RRV a significant problem for landscapers and horticulturalists. Non-commercial, wild rose species of the Rosa genus, such as the meadow rose (R. blanda), swamp rose (R. palustris), Carolina rose (R. Carolina), prickly wild rose (R. acicularis), and burnet rose (R. spinosissima), are the exceptions and show only minimal signs of susceptibility to RRV. RRV is primarily distributed throughout the eastern United States ranging from the Eastern coast of New England to the base of the Rocky Mountains. In short, RRV is a destructive and highly lethal rose pathogen that poses a significant threat to the commercial rose industry. This report seeks to highlight what we currently know about RRV and to highlight the areas where future research needs to be conducted.

Signs and Symptoms of RRV

Figure 2: Elongated stem phenotype and mite damage indicative of RRV. Phyllocoptes fructiphilus transfers RRV to the rose. The picture demonstrates the symptoms of RRV, i.e. vibrant red foliage, stem elongation, and increased thorniness. The mites feed primarily on new rose growth and are found most commonly found within the tips of rose shoots. The rose shoots are where P. fructiphilus reproduce and feed. Photograph by USDA, Agricultural Research Service.

RRV infection is characterized by excessive thorniness, over-zealous leaf proliferation, leaf mosaic patterning, red pigmentation, and witches’ broom (see Figure 1). The symptoms of Rose rosette virus (RRV) disease are quite complex but can be split up into three parts. Stage 1 represents newly infected plants. Stage 1’s earliest symptoms found in susceptible Rosa spp., include a vibrant magenta, almost purple coloration on the abaxial (underside) veins which extends out into leaves, reduction in flowering, and increased density of thorns on the shoots. Another common symptom found in Stage 1 is that affected leaves are deformed, chlorotic with red pigmentation, and elongated (see Figure 2). Stage 2 RRV infection exhibits early rosette character in which leaves display a mosaic pattern with vibrant red coloration. The leaves also tend to be highly elongated, disfigured, and exhibit a ruffled pattern. Like in Stage 1, lateral buds break dormancy early and grow before the plant is ready. The breaking from dormancy possibly suggests that some of RRV’s pathogenicity results from interference with abscisic acid signaling. Petioles are significantly shorter, which gives the classic rosette phenotype on symptomatic shoots. Growth rate on unaffected areas of the rose bush is often greatly reduced. Flowering is extremely rare in affected RRV areas of the plant. The final stage, Stage 3, is characterized by a large reduction in leaf size, with leaves becoming almost hair-like and intensely red in hue. Rosette formation is fully characterized by the formation of the described witches’ broom phenotype. Petioles are short, almost all lateral buds break dormancy, growth is weak, and the whole plant is characterized by a vibrant, deep red coloration. For rose plants that are in Stage 3, most are unable to survive freezing conditions. As there is no cure for RRV, most rose plants that are susceptible to the disease will die. Typically, a mature rose plant that becomes infected with RRV, will succumb to disease after a period of three to five years.

Isolation History of RRV

The first indication that RRV was indeed a virus came when large virus-like particles were observed with scanning electron microscopy in Rosa multiflora and commercial roses in Northern Arkansas. In the same study, the double-membrane characteristic of the spherical envelope was observed for the large virus-like particles. The next breakthrough in the isolation of RRV came with the isolation of dsRNA from infected rose tissue. dsRNA, being something that is prevalent and unique to viruses, strongly suggested that the causative agent for rose rosette disease was a virus.

Up until 1995, rose rosette disease (RRD) was thought to be caused by a virus or a phytoplasma; a phytoplasma can be equally as small as a virus. A phytoplasma was ruled out as the cause of rose rosette disease, by the lack of a DAPI DNA stain in isolated cells, no reversion in symptoms when plants were treated with tetracycline, and no amplification detected using known primers of phytoplasmas via PCR analysis .

The negative-sense RNA nature of RRV was finally elucidated in 2011, by using degenerate oligonucleotide primed reverse transcriptase PCR to amplify dsRNA. The purification of emaraviruses from inflected plants has been challenging to researchers due to the enveloped nature of the virus particles as well as by the low titre. This potentially explains why RRV and related emeraviruses were reported only having four genomic RNA segments rather than more. Recently, from more sensitive analysis, another three RNA segments were isolated and detected in RRV . There are many things not fully understood about RRV. At the foremost of this list is the pathogenicity of RRV. Future studies need to be conducted in order to elucidate the mechanism of entry for RRV, the replication of RRV, and the possible latency of RRV.

Virion and Genome Structure

Figure 3: An –ssRNA viral phylogenetic tree based upon sequence relationship between the RDRP protein and the emaravirus RLBV. The gray box represents viruses within Emaravirus. Branch lengths represent a proportional difference between genetic sequences; bar, 0.4 expected amino acid changes per site. Emaraviruses that are listed: Raspberry leaf blotch virus (RLBV), Rose rosette virus (RRV), Fig mosaic virus (FMV), and European mountain ash ringspot-associated virus (EMARaV)

The rose rosette viron particle is of a large size ranging from 120-150nm. The RRV viron particle is comprised of a symmetrically helical enveloped ribonucleocapsid and has been described as having a spherical shape. Rose rosette virus is a negative-sense RNA virus and was identified in 2011 as a member of the genus, Emaravirus . Like European mountain ash ringspot associated virus (EMARaV), RRV has four common RNA coding segments, RNA1-RNA4, as well as three other uncharacterized RNA5-7 segments. The RNA1-4 segment protein products are referred to p1-p4 respectively (see Figure 4). In RRV, the RNA1, RNA2, and RNA3 each contain an open reading frame (OPR) that putatively encodes for RNA-dependent RNA polymerase (RdRp, RNA1), glycoprotein precursor (RNA2), and nucleocapsid (RNA3). Fascinatingly, segmental RNA from the RRV genome was found to be uncapped, but mRNA of RRV transcripts were found to be capped with 7-methylguanylate just like all eukaryotic mRNA transcripts.

In RRV, RNA4 (p4) function has not be elucidated. However, RRV p4 is closely related to the virus, raspberry leaf blotch emaravirus p4 (RLBV, see Figure 3). In a study looking at p4 in RBLV, it was shown that the p4 protein localizes to the plasmodesmata, hinting that the protein is a viral movement protein otherly known as an MP. Upon further investigation the p4 protein from RLBV rescued cell-to-cell movement of a MP-deficient potato virus X (PVX), which provides evidence that the p4 protein in RRV is likely an MP protein. There are direct genetic indications that RRV p4 is a cell-to-cell movement protein with the largest piece of evidence coming from the fact that there are dnaK and ATPase motifs in the RRV RNA4 segment, which codes for p4. dnaK and ATPase domains are required for plant viral movement proteins. It is likely that p4 is a movement protein. However, until an experiment like that of Chulang Yu and colleagues (2013) is conducted in an RRV infected host, we will not know for certain the function of RRV p4.

Unlike RRV, other emaraviruses such as RLBV has at least eight putatively encoding RNA segments . Due to the low titre and enveloped nature of RRV, RRV may be comprised of more RNA segments. In a follow-up isolation study by Di Bello and colleagues (2015), three new RNA genome segments were found. However, it is possible that fragile or low concentration RNA segment regions may have gone undetected in RRV samples. In order to build a better map of the RRV genome, future dsRNA isolation studies of RRV will have to be conducted in order to confirm that there are only seven RNA segments.

Genomic Methods of Detection for RRV:

Figure 4: Genetic map of RRV’s four major RNA segments

Figure 5: RT-PCR detection sensitivity assay that demonstrates detection of RRV from 1pg to 1fg. Wells were loaded with cDNA from RRV infected tissue. Lanes 1-4 were loaded with 1pg, 100fg, 10fg, and 1fg of RRV infected cDNA respectively. Lanes M represents the ladder and lane N represents the cDNA for a healthy non-RRV infected plant.

Traditionally, many viruses are detected through the use of antibody based methods. For example, enzyme linked immunosorbent assays or ELISAs are a common and effective method for quickly identifying if a particular organism is infected with say tobacco mosaic virus (TMV). Just like TMV, an ELISA can be utilized to detect the presence of RRV. A direct ELISA functions by immobilizing the target viral antigen on a polystyrene plate coated with a non-reacting protein such as BSA. After immobilization, the primary antibody is added with a conjugated enzyme. The conjugated enzyme binds specifically to the antigen as well as the primary antibody. A substrate is then added for the enzyme such as PNP solution to detect a color reaction that can quantitatively be read using a spectrophotometer. Thus, the higher the concentration of the primary antibody, the more target viral antigen is present. A few downsides with viral ELISAs are that they require a significant amount of biochemical knowledge of the virus being studied. It can be difficult to find monoclonal antibodies that can recognize the target virus, and the antibodies themselves can be quite costly. Lastly, ELISAs are also not as fast or specific/discriminatory as other nucleic acid, PCR based methods. Although highly specific, ELISAs they cannot distinguish between antigenically identical analytes, i.e. different molecules recognizing the same antibody.

As of today, the most sensitive and effective method of RRV detection is through RT-PCR. The developed RT-PCR assay by Dobhal and colleagues (2016) can detect as little as 1fg (femtogram) of RRV in roses infected with RRV (see Figure 5). The RT-PCR method outlined is a cheaper and faster analysis methodology than using standard PCR probe-based analyses. The basic RT-PCR RRV identification protocol utilizes primers that were designed to amplify sequences of the RRV nucleocapsid gene p3 located within the RNA3 region, which is believed to be highly conserved in RRV. RT-PCR was optimized for RRV isolation and identification of RRV via adjustments made in annealing temperature, production of higher affinity primers, and concentrations of reagents.

Ecology, Epidemiology, and Transmission:

Figure 6:Phyllocoptes fructiphilus is very small eriophyid mite and extremely difficult to be seen without microscopy magnification. Similar to all eriophyid mites, P. fructiphilus has two pairs of legs at the back of a tubular-like body. Photograph by USDA, Agricultural Research Service.

The primary vehicle in transmission of RRV is the eriophyid mite, Phyllocoptes fructiphilus. As of today, eriophyid mites are the only known animal vector to transfer RRV (see Figure 6). Grafting has also been demonstrated to transmit RRV. Eriophyid mites feed off infected RRV rose tissue and carry virons within their probiscous, transferring RRV when they come into contact with another rose plant. Although P. fructiphilus cannot fly, they can and do move passively long distances via air currents to nearby roses, subsequently infecting new roses. Even though the mite RRV vectors can be transmitted through wind, the risk of infection for roses that 150-300m away from another infected rose plant is considered minimal. The fact that the close proximity of infected host rose plants to unaffected host rose plants is needed for transmission (~20m); is immensely valuable to landscapers and rose horticulturalists. Transmission of RRV can subsequently be mitigated simply by placing large distances between rose planting.

RRV was first detected in Manitoba, Canada; California; and Wyoming. Since then the disease has spread across the United States and by the early 2000s cases of RRV had been detected in all of the 48 states with the greatest impact being felt east of the Rocky Mountains. The host abundance is larger/more widespread in the Eastern U.S. as well as the fact that P. fructiphilius is less fit for the drier climates of Western States. It has been postulated that the spread of RRV has been expedited by the widespread coverage of the invasive species Rosa multiflora (Multiflora-Rose). R. multiflora is native to Eastern China, Korea, and Japan. R. multiflora is highly susceptible to RRV. R. multiflora became a ubiquitous invasive species across the Midwestern and Eastern United States after the 1930s. Starting in the 1930s, the U.S. Soil Conservation Service recommended and distributed R. multiflora seeds and saplings for use in erosion control and to be used as “living fences” for livestock. However, due to the proliferative nature of R. multiflora, the plant soon became a common pest/noxious weed in several U.S. states. Because of how widespread R. multiflora is across the U.S., it serves as an RRV pool upon which P. fructiphilus mites can transmit the disease to commercially relevant species of Rosa.

In a field experiment, RRV was demonstrated to increase R. multiflora mortality from 1.1% to 44.3%, for 180 plants across a two year period. Since rose rosette disease effectively infects via P. fructiphilus and kills the invasive plant R. multiflora, RRV has been proposed as a potential biological control for R. multiflora. The downside of having a significant RRV pool is that the disease can more readily be transferred to commercially relevant roses.

Evolution

RRV’s exact aetiology is currently unknown. Many conjecture that RRV came from the indigenous R. multiflora populations in China, Korea, and Japan. However, there has not been evidence presented supporting this claim. One thing that we do have a clearer picture of is RRV’s phylogenetic history. An isolation and phylogenetic study of RRV conducted by Laney et al. (2011), classified RRV as an Emaravirus with close connections to European mountain ash ringspot-associated virus (EMARaV) and Fig mosaic virus (FMV). From isolated p3 and p4 protein domains in RRV, they demonstrated 97%-99% exact nucleotide identities to FMV and EMARaV p3 and p4 protein domains. Based on RNA-dependent RNA polymerase sequence similarity, Emaraviruses are distantly related to other negative-sense RNA viruses, such as tospoviruses and tenuivirus.

A fascinating aspect of RRV is the seven part RNA, segmented genome. Evolutionarily, an RNA segmented genome could theoretically allow for replication to be spread out over more of the host cell’s resources, thus making replication faster for RNA segmented genomes. Ultimately, this would confer a replicative advantage for RNA segmented genomes. Nevertheless, this has only been theoretically conducted and not demonstrated in a viral model setting. Another potential advantage of having a segmented genome is that the rate of reassortment would be predicted to be higher because there are simply more parts to be linked together or shuffled around. Reassortment events, in segmented RNA genomes, could potentially remove deleterious configurations and/or generate advantageous genomic configurations.

The hypothesis that segmented genomes have a recombination advantage over non-segmented genomes has been postulated. The rationale is that the segments will potentially be closer together allowing for homologous regions to interact and recombine more readily in segmented RNA genomes. However, at this time, the data does not support that recombination occurs more readily in segmented RNA genomes. In an experiment looking at the tripartite RNA cucumber mosaic cucumovirus, recombination and reassortment rates were quantitatively observed to be infrequent. Only a 7% recombination rate was observed between segments, and the recombinants were conserved within the population.

A problem with long single stranded RNA (ssRNA) viruses is their instability as chain length grows. Short chains are much more stable than long ssRNA chains. For the sake of stability, less coding genetic material can be added to the RNA chain, which in turn means less coding information can be fit on the RNA chain. Thus, there is a trade-off between chain length (the total amount of genetic material) and particle stability. The segmentation of the RNA genome presents itself as a possible solution. Data has been presented that suggests virally segmented genomes serve as a molecular solution to the trade-off between the stability of the RNA segment and length of the RNA segment. Genomic segmentation serves as a way to maximize the genetic content of a genome while overcoming the detrimental effect of RNA chain length instability.

Commercial Impact

Roses (Rosa spp.) are of immense commercial importance for their use in landscaping, aesthetic value, industrial products, and cosmetic products. To emphasize the economic importance of roses; roses have a total wholesale value of $194 million in the United States.

Is it necessary to research RRV and understand its underlying mechanism of pathogenicity? Although, there has not been an official report on the economic impact of RRV related damages, it is believed to be well into the millions. The disease is primarily contained to the United States but recently RRV has been spotted in India. The spread of RRV outside of North America has been raising concerns throughout the globe, considering that two-thirds of all of the 40 billion dollar cut flower market is comprised of roses. RRV, although difficult to transmit, has a high lethality and can decimate densely populated rose populations. For example, in 2012, RRV decimated the Tulsa Municipal Rose Garden in which thousands of rose plants had to be eradicated. Due to widespread nature of RRV across the Southern U.S. and Midwest, it is proving to be a common pest for the average home gardener and nurseries that carry rose plants. I believe the economic impact of RRV calls for a better understanding of RRV itself so that we can combat this disease.

Management

The most effective management of RRV is through controlling the vector of transmission, P. fructiphilus. Listed below are effective and common management practices that can greatly curtail the transmission and severity of RRD from RRV.
1. Once a rose has been identified with RRV, the plant should be removed and either placed in a plastic air-tight bag for disposal or be burned. Removal of infected RRV roots should also be conducted.
2. Pruning roses can potentially eliminate mites and eggs. The eggs and mites are predominately found within the new growth areas and petiole areas of the rose.
3. Removal of R. mulitflora roses in the area of your cultivar roses, which is best done by mechanical removal, i.e. cutting them down during the growing season. Herbicide applications can also be made to the stem of muliflora roses to hasten their death.
4. Currently, it is unknown which pesticides are effective control measures for the reduction of eriophyid mites as they often hidden from observation due to their placement in the buds on growing apical tissue.
5. Phytocides, although unproven, may be an effective measure in managing the population of eriophyid mites.
Solely chemical control of eriophyid mites is not advised due to the fact that at least nine species of the mites have developed significant pesticide resistance. Instead, a combination of the methods listed above is the most effective way to stem the tide of transmission of RRV.

Currently, research is being conducted on making RRV resistant roses. There are two main approaches that are being done to create an RRV resistant rose. The first involves traditional breeding between commercially susceptible rose varieties and resistant non-susceptible wild Rosa varieties. The alternative approach is through genetic engineering in which researchers are trying to identify resistance genes or R-genes that confer resistance to RRV. One potential way in which researchers can possible discover and isolate R-genes that confer RRV resistance is through Quantitative Trait Locus (QTL) mapping of nucleotide-binding site/leucine-rich repeat like sequences (NBS-LRRs). NBS-LRRs are genetic motifs commonly found in R-genes.

Conclusion

Rose rosette virus is a serious plant pathogen that has a high rate of mortality for an infected plant. Ecologically, RRV is serving as a biological control for the invasive species R. multiflora but conversely is a decimating disease to ornamental rose species. Currently, we do not even understand how RRV works in terms of its pathogenicity. This leaves two folds of research that need to be conducted: 1) Research into breeding/genetically engineering resistant RRV roses and 2) research into determining the mechanism of RRV’s pathogenicity.

Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2017, Kenyon College.

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