Black stems on roses

How to Get Rid of Black Spot on Roses

It starts gradually — a few yellowed leaves dropped to the ground, a few dark brown or black spots on the leaves you can easily attribute to just natural aging. Then suddenly, your rose bush looks terrible! Leaves are falling off at a rapid clip. Before tumbling to the ground, the leaves are dotted with black spots or splotches that fade into the leaf itself. As the days progress, nearly all the leaves yellow and fall from your prized roses, leaving a thorny skeleton behind. What happened? Was it an insect that attacked overnight or something else?

Black Spot on Roses

If this scenario sounds familiar, welcome to the bane of the rose gardener’s existence: black spot on roses. Black spot (Marssonina rosae or Diplocarpans rosae) is a fungal disease considered to be the most serious rose disease in the world. The parasitical fungus spreads rapidly through direct contact among roses — usually at an infected grower’s site or in the home garden — or through wind-borne spores. Once black spot takes hold on a rose bush, it can quickly decimate the plant or weaken it to the extent that the plant dies.

What Causes Black Spots on Rose Leaves?

Before addressing horticultural practices to help prevent black spot disease, it’s important to understand what causes black spot on rose leaves.

Black spot is caused by a fungus, Marssonina rosae or Diplocarpans rosae. Scientists give this fungus two names to signify its normal state — Marsonnina — and its reproductive state — Diplocarpans. Most rose gardening sites simply refer to it as Diplocarpans rosae since it causes the most trouble when it’s reproducing and spreading throughout your garden, leaving behind noticeable yellow leaves with black spots on rose bushes.

Infected plants produce spores, and the spores are carried along by the wind until they land on the ground or on a plant. The spores must be moist for several hours in order to develop into full-fledged black spot, which is why the disease is more prevalent in areas with high humidity. Rainfall, mist, fog or even lawn sprinklers can provide sufficient moisture for black spot to thrive.

About two weeks after the spores infect a plant, the telltale black spots develop on the leaves. These black spots are what biologists call “fruiting structures.” The fruiting structures or spots produce spores, which continue to infect other areas of the same plant, new canes or other roses in the garden.

Black spot is a tenacious fungus — it thrives in warmth and moisture, but it tolerates a wide range of conditions including extreme heat and cold. Even a harsh winter won’t kill the spores lying dormant in your garden. To get rid of black spot disease on roses, you’ll need to try one or more of the four steps listed later in this article.

Some gardeners with severe infections may need all four steps to stop black spot in its tracks. This may seem extreme, but like many fungal diseases, black spot is tough to eradicate completely from the garden.

Symptoms of Black Spot Infection

At first, roses show no signs of infection. After the spores alight on a rose bush, it takes about two weeks for them to germinate and develop into mature fungus that can reproduce. Signs of black spot infection start small but rapidly increase, especially if the weather is particularly hot and humid.

Symptoms of black spot infection include:

  • The telltale black spots or dots on the rose bush’s green leaves. These spots may start as a dark, chocolate brown and turn darker over time. They can be anywhere on the upper surface of the leaf. The edges are irregular, almost feathery, and extend out from the darker center.
  • As the spots grow larger, the leaves turn yellow. The yellow leaves with black dots on roses form clusters of infected leaves. Soon, the whole plant looks sick. Eventually, leaves fall off the plant as their ability to make food (photosynthesis) is compromised by the infection.
  • Both old and new canes can also be infected with black spot. Black spot on canes looks like a purple dot or blotch. If the cane dies, the pathogen remains in the cane, so new canes are immediately infected. Black spot can live inside a rose’s canes over the winter, too.

Why Is Black Spot Bad for Roses?

Black spot looks ugly, of course. Yellowed leaves on roses aren’t attractive, and when they fall off, they leave a bare, skeletal plant. More importantly, black spot weakens the entire plant so that it may eventually die.

Plants produce energy within special cells of their leaves called chloroplasts. These cells are like little food factories, using the sun’s rays to transform water and carbon dioxide into energy for growth, maintenance and reproduction. This process is called photosynthesis.

Because black spot defoliates roses, there are fewer leaves to produce energy for the plant. The plant cannot produce enough new leaves fast enough to make up for the shortfall. As new leaves emerge, they’re also infected, and soon the plant doesn’t have any way left to make its energy supply. Although some plants can survive a year of this, two or more years in a row weakens them to the point at which they die, or a harsh winter kills an already weakened plant. That’s why black spot is such a dreadful disease.

Some tough garden roses can, in fact, survive a black spot infection. Roses are an ancient plant. Fossilized specimens indicate they have been around for 35 million years. Individual specimens and some rose species do indeed have a natural resistance to black spot, but many hybrids, particularly hybrid tea roses, are extremely susceptible to black spot disease.

Banish Black Spot From Your Garden in Four Steps

Armed with a good description of black spot disease, you’ve determined the problem in your rose garden is most likely caused by this pest. Now it’s time to take action.

There are four steps you can take to combat black spot disease on roses:

Step 1: Change Your Gardening Habits to Discourage Black Spot

Several gardening habits provide the ideal conditions necessary for the black spot spores to develop into full-blown disease. Here are five easy ways to help prevent black spot on roses.

Clean up your garden in the fall. Snip dead branches on perennials and shrubs and prune your roses. Don’t compost these garden scraps. Instead, bag them and set them out for the trash, hence, if any black spot spores are on the canes, they’ll go to the landfill and not back into your compost pile where they may eventually infect yours or someone else’s roses.

Water at the base. Many automated watering methods, like sprinklers, tend to wet the leaves without delivering water beyond the drip line – boundary created by the foliage extending over the plant’s central stem. It’s within that drip line that the plant’s roots can take up water, and that’s where to direct your spray of water to be the most effective. Water the ground near the roots instead of soaking the bush with a spray from above.

Water in the morning. Evening watering schedules promote mold and fungus, including black spot. That’s because moisture and darkness make ideal conditions for these microorganisms to grow on plants. Morning watering gives the sun’s rays a chance to dry splashes of water on the leaves. Switch your watering schedule to the morning instead evening.

Clean and sterilize your tools. It’s a good idea to clean your pruners every time you use them. Keep a bottle of rubbing alcohol near your pruners and a clean rag — just wipe the blades with alcohol before putting them away. Dip or rub the blades in alcohol before using them on another plant, too. When you prune your roses, you create an open wound through which infection can enter the canes. Alcohol kills bacteria, mold and fungi.

Plant roses in full sun. Roses don’t do particularly well in shade. Partial shade, especially morning shade, keeps dew on the leaves just long enough to provide the conditions that black spot loves. Grow roses in full sunlight only.

Changing your gardening practices may not entirely prevent black spot, and they do not treat black spot if it’s already rampaging through your garden. What if you’re doing everything right, yet your roses still have black spot? It’s time to move on to step two in our list of steps to tackle black spot: Try natural remedies.

Step 2: Know the Remedies

Botanists have long searched for an effective, natural remedy for black spot on roses. Milk, a popular folk remedy, has been deemed ineffective by researchers at Washington State University. Although milk can be useful to help various foliar sprays stick to leaves, it may actually cause other diseases that can harm your roses.

So which natural cures do work for black spots on roses? A paper published in the Journal of Medicinally Active Plants lists the essential oils of English thyme and “Scotch” spearmint, two common plants, as potentially effective in the treatment of black spot disease.

The essential oils of these two garden herbs were tested against a control of fungicide and a second of water, and the results indicate that English thyme and “Scotch” spearmint both provided antifungal properties that lessened the severity of black spot lesions. Other herbal essential oil extracts were also tested, including that of sweet basil and holy basil, two other plants with alleged antifungal properties. Neither species of basil produced notable results.

Neem oil, produced by the Asian Neem tree, offers some relief of black spot. Neem has notable antifungal properties that seem to work well on roses. Neem oil is also useful against powdery mildew, which is another fungus roses tend to get.

Step 3: Commercial Black Spot Sprays

By far the most popular method of treating black spot on roses is through the use of conventional sprays. Sulfur compounds are effective at treating black spot. Safer® Brand Garden Fungicide uses sulfur as the active ingredient and is available in a convenient spray bottle or concentrate that can be mixed according to package directions for a foliar spray.

When using commercial fungicides in your garden, be sure to use only the recommended amount according to the label directions. More may not necessarily be better. Be sure to wash your hands and clothing after application, and dispose of the container according to the label on the package.

Step 4: Choose Roses Resistant to Black Spot

Rose growers should keep their eyes open for plants that aren’t susceptible to black spot. Disease-resistant roses should be grafted into hardy root stock to produce new plants with strong growth and resistance to common diseases. They may also breed new varieties of roses by crossing two kinds that are naturally disease resistant.

Thanks to the test of time and long-standing exposure to black spot, older rose varieties tend to have natural disease resistance. While many of these older roses have a different flower shape and petal configuration than what you may imagine when you hear the word “rose”, they often have a stronger fragrance, and they tend to be vigorous, healthy plants. It’s worth a try if you love roses but have trouble growing them due to black spot disease.

Keep in mind that roses may be resistant in one location, but not when planted in another. That’s because there are numerous strains of the black spot fungus. For example, a rose may be resistant in Oregon to one strain but susceptible to the strain living in Pennsylvania. Always try to purchase plants grown locally for your best chance at roses resistant to black spot.

Roses naturally resistant to black spot disease include:

  • The Carpet Rose®: Flower Carpet roses are easy to care for and low-water tolerant. They have won numerous awards for their disease resistance, including Germany’s strict ADR awards where no chemicals are allowed to be used in the trials.
  • Drift Roses: These ground cover roses only grow a little over a foot high and don’t require pruning. The Coral Drift and Sweet Drift varieties are fragrant.
  • Floribunda Roses: Floribunda roses are a shrubby type of rose bush that produces copious sprays of small, rose-shaped flowers. Most shrub roses or Floribunda roses are hardy and disease resistant. Some are also resistant to rust and other fungal diseases in addition to being resistant to black spot.
  • Meilland Hybrids: Originally grown in the south of France, Meilland hybrids are now available worldwide and are cultivated for disease resistance.
  • Knock Out Roses®: These are a new rose hybrid produced by Star Roses and Plants. Available at nursery and garden centers nationwide, they are said to offer better disease resistance than similar plants.

Among the hybrid tea roses, several older varieties offer black spot resistance. These include Mr. Lincoln — a classic red tea rose — Tropicana — an orange variety — and Miss All American Beauty — a pink rose.

You can find black spot-resistant rose varieties from among all types of roses including climbing roses, miniature roses and more. With over 50 strains of black spot fungi identified, not all roses are resistant to each strain. Strains are found locally, so roses known to be black spot-resistant in local gardens are likely the best ones to plant in your garden for disease resistance.

Black Spot Blues? Don’t Despair

Many roses naturally survive an outbreak of black spot. The earlier you begin treating your roses for black spot the better chances it has at recovering.

One rose, the Hildesheim climbing rose, has been verified by scientists to be over 1,000 years old. If a rose can survive 1,000 years of exposure to black spot and other diseases, maybe your rose can survive, too.

Rose Diseases

Roses are one of the most popular and versatile flowering shrubs grown throughout South Carolina. Most roses require a lot of care to grow and bloom properly. One of the most common causes of failure with roses is poor disease control. The three most serious diseases of roses in South Carolina are black spot, powdery mildew, and stem canker and dieback. For more information on roses see HGIC 1172, Growing Roses.

Remember that different types of roses vary greatly in their resistance to diseases and the maintenance they require. To grow roses successfully, you must select varieties that require an amount of care equal to that which you are able to provide. Shrub type roses bloom beautifully with few chemical controls needed, while the more susceptible varieties such as hybrid tea roses require an effective spray program to be in place before the growing season begins.

Black Spot

Black spot is a common and serious rose disease often reaching epidemic proportions in a season. The disease is caused by the fungus, Diplocarpon rosae. It is most severe after long wet, warm periods in the spring. Symptoms occur on rose leaves as circular, black spots surrounded by a yellow area. Infected leaves often drop from the plant. Infection continues throughout the summer months. The immature wood of first year canes develops raised, purple-red irregular blotches. Plants become stunted and produce fewer, paler flowers. By mid-summer severely infected plants may have lost all of their leaves.

Prevention & Treatment: The spread of black spot can be reduced and future infections minimized by following these cultural practices:

  • Plant Resistant Varieties: (See the following list)
  • Maintain Good Sanitation: Sanitation practices are critical in reducing future disease development. In the fall or winter remove all old leaves on the ground along with any mulch that has been contaminated with infected leaves. Replace with a fresh layer of mulch before new rose growth begins in the spring.
  • Remove & Destroy Infected Canes: Canes affected by black spot have dark or reddish areas (lesions). Severely infected plants should be pruned back in the winter or early spring to within 1 to 2 inches of the bud union, according to variety and cultivar. During the growing season, remove and dispose of infected leaves as they appear.
  • Keep Leaves Dry: It is best not to syringe plants with water, and do not use overhead irrigation, especially not in the late afternoon or early evening. Soaker hoses are an excellent way to water roses and to conserve water. Promote rapid drying of leaves by planting roses in the full sun. Space new plants far enough apart to allow for good air circulation.

Use fungicide sprays to control black spot effectively, even on resistant varieties. A rigorous fungicide program must be followed during conditions that favor disease development for susceptible cultivars. Select one of the following fungicide sprays, if disease is severe enough to warrant control: chlorothalonil, mancozeb, myclobutanil, propiconazole, or copper fungicides. See Table 1 for examples of products. Apply all chemicals according to directions on the label.

Powdery Mildew

Powdery mildew is another widespread and serious disease problem of roses. It is caused by the fungus, Sphaerotheca pannosa var. rosae and produces a grayish-white powdery substance on the surfaces of young leaves, shoots and buds. Infected leaves may be distorted, and some leaf drop may occur. Flower buds may fail to open, and those that do may produce poor-quality flowers. It can occur almost anytime during the growing season when temperatures are mild (70 to 80 °F), and the relative humidity is high at night and low during the day. It is most severe in shady areas and during cooler periods.

Prevention & Treatment: Rose varieties differ in their susceptibility to powdery mildew, thus resistant varieties are the best defense against this disease. A film of water inhibits infection, so in years when rainfall is high during spring and summer, control measures may not be needed until the drier months of late summer. Remove and destroy diseased leaves and canes during the growing season. Rake up and destroy leaves under the plant in the fall.

If the disease is severe enough to warrant chemical control, select a fungicide that controls both black spot and powdery mildew. Fungicide sprays recommended for use in the home garden include: propiconazole, thiophanate-methyl, myclobutanil, sulfur, neem oil (clarified hydrophobic extract), or baking soda mixed with horticultural oil. See Table 1 for examples of products. Apply all chemicals according to directions on the label.

The following roses have some disease resistance;

Black Spot – Resistant:

  • Hybrid tea: ‘Pride N Joy’
  • Floribunda: ‘Sexy Rexy’
  • Grandiflora: ‘Prima Donna’

Black Spot & Powdery Mildew – Moderately Resistant:

  • Hybrid tea: ‘Duet,’ ‘Eiffel Tower,’ ‘Grand Slam,’ ‘Jamaica,’ ‘Matterhorn’
  • Floribunda: ‘Golden Slipper,’ ‘Saratoga’
  • Grandiflora: ‘Camelot,’ ‘John S. Armstrong,’ ‘Pink Parfait,’ ‘Queen Elizabeth’
  • Shrub roses: ‘All That Jazz,’ ‘Carefree Wonder’

Black Spot, Powdery Mildew & Cercospora Leaf Spot – Resistant

  • Rugosa roses: ‘Blanc Double de Coubert,’ ‘Fru Dagmar Hastrup’ (‘Frau Dagmar Hartopp’) ‘Rugosa Alba,’ ‘Topaz Jewel’
  • Alba rose: ‘Alba Semi-Plena’

Stem Canker & Dieback

Cankers usually appear as dead or discolored areas on rose canes and vary in color from light tan to dark purplish brown. They are caused by various species of fungi, including Botryosphaeria, Leptosphaeria, Coniothyrium and Cryptosporella. These fungi enter healthy canes through wounds caused by winter injury, improper pruning, wind, hail damage, or flower cutting. Cankers can enlarge until they entirely surround the cane, and/or reach the base (crown) of the plant spreading to other canes or killing the plant. They commonly occur on roses that have been weakened by black spot, poor nutrition or winter injury.

Prevention & Treatment: There are no fungicides specifically available to control stem canker. Keep plants healthy by controlling black spot, powdery mildew and insects. The following cultural methods can help minimize disease development.

  • Avoid Injury to the Plant During Transplanting, Cultivating, Pruning, & Flower – Cutting: Wounds are a major way the fungus enters the plant.
  • Prune Properly: To prune an outward facing bud. This will help to avoid too many branches growing into the center of the plant that may cross and rub together.
  • Remove & Destroy all Infected or Dead Portions of Canes Immediately: Make all pruning cuts well below the diseased areas, and prune about one-fourth inch above an outward-facing bud node, without cutting the nodal tissue, at a 45-degree angle. Prune live canes in the spring, not fall. Disinfect cutting tools after use on a diseased plant in a solution of 1 part household bleach to nine parts water.

Rust

Rose rust is a disease caused by the fungi Phragmidium species. It causes orange-colored spots to appear on stems and leaves. When rust is severe, an orange dust-like substance may be present on the plant surface and on the ground below the plant. Rose rust attacks all plant parts except the roots and petals. Severely diseased leaves of highly susceptible cultivars may turn yellow or brown and drop.

Prevention & Treatment: Provide good air circulation. Do not plant roses in crowded areas and prune plants to keep the centers open. Water plants before noon and avoid getting the leaves wet. Remove and destroy diseased leaves and plants. Fungicides containing myclobutanil, mancozeb or propiconazole are recommended for homeowner use. See Table 1 for examples of products. Apply all chemicals according to directions on the label.

Botrytis Blight

Rose flowers and buds are often infected with the gray-brown fuzzy growth of the gray mold fungus Botrytis cinerea. The fungus is most active when temperatures are 62 to 72 °F and conditions are moist. Infected canes have discolored sunken areas (cankers) and dieback that can extend down the stem from the flowers. Diseased flower petals have small, light-colored spots surrounded by reddish halos, which can quickly expand into large, irregular blotches. Buds fail to open and often droop. Thrips can cause similar damage to half-open buds, so inspect plants carefully.

Prevention & Treatment: Keeping the area clean is more important than anything else. Collect and discard all fading flower blossoms and leaves. Provide good air circulation, and avoid wetting the leaves when watering. Disease easily develops on canes that have been damaged, on canes that are kept too wet by the use of manure mulch, or on wet leaves. If chemical control is necessary, fungicides containing thiophanate methyl, chlorothalonil or neem oil (clarified hydrophobic extract) are available for homeowner use. Use neem oil on a trial basis, especially on open blooms and during hot weather. Neem oil is a rather weak fungicide. On dormant bushes copper fungicides can be used. See Table 1 for examples of products. Apply all chemicals according to directions on the label.

Rose Rosette Disease

Rose rosette disease is an untreatable rose disease caused by the Rose rosette virus (RRV), and is spread and introduced into the rose during feeding by the rose leaf curl mite (Phyllocoptes fructiplilus). This extremely small eriophyid mite feeds on cell sap of the tender stems and leaf petioles. The rose leaf curl mite alone causes little damage while feeding, but if it is a carrier of RRV, symptoms begin to appear in the rose typically within one to three months.

Roses exhibit reddened terminal growth on infected branches, and the stems become thicker and more succulent than those on unaffected parts of the plant. These stems exhibit an abnormally high number of pliable thorns, which may be either green or red. Rose leaves that develop on infected branches are smaller than normal and may be deformed similarly to herbicide injury by 2,4-D. Lateral branches may grow excessively from main stems and create a witch’s broom symptom quite like glyphosate (Roundup™) injury on roses. Flowering is reduced, and the petals may be distorted and fewer in number.

Rose with Rose Rosette Disease showing symptoms of reddened new growth, thicker stem, excessive thorns, and smaller leaves.
Meg Williamson, Plant and Pest Diagnostic Clinic, Clemson University

These symptoms generally become evident in the late spring to early summer and progress during the growing season. Once the rose becomes infected, RRV moves throughout the plant and the entire plant is infectious. By the time symptoms are evident in a rose, it already may have spread to adjacent plants by the movement of the eriophyid mites. Infected plants typically die within a couple of years.

Prevention & Treatment: The wild multiflora rose is very susceptible to the rose rosette disease, so any nearby wild plants should be removed and promptly disposed. Any infected, cultivated roses should be immediately removed, then burned or bagged. Also remove any roots, which might re-sprout later. Do not leave an uprooted infected plant in the garden, as the mites may leave this rose for other nearby plants. Always space rose plants so they do not touch.

Because RRV is systemic within the infected rose plants, grafting asymptomatic stems onto other rose plants will transmit the virus. Pruners used on diseased plants must be disinfested with rubbing alcohol or a dilute bleach solution before being used on uninfected plants, as sap on the pruners is contaminated with the virus.

To reduce the spread of the eriophyid mites from the site of an infected rose, nearby roses can be treated with a bifenthrin spray every two weeks between April and September. This may prevent additional plants from becoming diseased. See Table 1 for examples of brands and products containing bifenthrin. Always check product labels for the correct active ingredient. Follow label directions for use.

Rose Mosaic

The symptoms associated with Rose mosaic virus (RMV) are highly variable. Yellow wavy line patterns, ring spots and mottles in leaves will occur on some varieties of roses sometime during the growing season. In general, symptoms are most evident in the spring. Yellow net and mosaic symptoms on the leaves are also associated with RMV and detract from the overall quality of the plant. Infected plants become weakened and are more sensitive to damage caused by other stresses, such as drought or low temperatures.

Prevention & Treatment: Virus-infected plants cannot be saved. Rose mosaic spreads slowly, if at all, in established rose plantings through root grafts. Infected plants should be removed from highly prized plantings and destroyed. Buy only healthy plants from a reputable dealer; especially avoid purchasing plants showing any mosaic symptoms.

Crown Gall

This disease is caused by a soil-inhabiting bacterium, Agrobacterium tumefaciens, which infects many ornamentals in the home garden. The symptoms are rounded galls, or swellings, that occur at or just below the soil surface on stems or roots. The galls are light green or nearly white when young. As they age, the galls darken and become woody, ranging in size from small swellings to areas several inches across. The galls disrupt the flow of water and nutrients traveling up from the roots and stems, thus weakening and stunting the top of the plant.

Prevention & Treatment: To prevent crown gall, select disease-free roses. Once a plant is infected, nothing can be done since there are no chemical controls available for crown gall. Avoid injury to the roots and crown of the plant during planting and cultivating because the bacteria enter through fresh wounds. Remove infected plants as soon as galls are observed. If possible, remove and discard the soil from the area where the infected plant was located. Disinfect all cutting and pruning tools that have been used near crown gall. To disinfect tools, dip them for several minutes in a solution of 0.5 percent sodium hypochlorite (household bleach).

Table 1. Pesticides for Rose Disease & Mite Control.

Pesticide Active Ingredient Examples of Brand Names & Products
Bifenthrin Ferti-lome Broad Spectrum Insecticide Conc.; & RTS
Hi-Yield Bug Blaster Bifenthrin 2.4 Conc.; & RTS
Monterey Mite & Insect Control Concentrate
Up-Star Gold Insecticide Concentrate
Bifen I/T Concentrate
Talstar P Concentrate
Chlorothalonil Bonide Fung-onil Concentrate
GardenTech Daconil Fungicide
Hi-Yield Vegetable, Flower, Fruit & Ornamental Fungicide Concentrate
Ferti-lome Broad Spectrum Landscape & Garden Fungicide Concentrate
Ortho MAX Garden Disease Control Concentrate
Tiger Brand Daconil Concentrate
Southern Ag Liquid Ornamental & Vegetable Fungicide Concentrate
Copper Fungicides Bonide Liquid Copper Concentrate (a copper soap); & RTU2
Bonide Copper Fungicide (copper sulfate); & RTU2
Camelot Fungicide/ Bactericide Concentrate (a copper soap)
Monterey Liqui-Cop Fungicide Conc. (a copper ammonium complex)
Natural Guard Copper Soap Liquid Fungicide Conc.; & RTU2
Southern Ag Liquid Copper Fungicide (a copper ammonium complex)
Horticultural oil3 Bonide All Seasons Spray Oil Concentrate; & RTU2
Ferti-lome Horticultural Oil Spray Concentrate; & RTS1
Monterey Horticultural Oil Concentrate
Southern Ag ParaFine Horticultural Oil
Summit Year Round Spray Oil Concentrate Add
Mancozeb Bonide Mancozeb Flowable with Zinc Concentrate
Southern Ag Dithane M-45
Myclobutanil Spectracide Immunox Multi-Purpose Fungicide Concentrate; & RTS1
Ferti-lome F-Stop Fungicide Concentrate
Monterey Fungi-Max
Neem oil Bonide Neem Oil Fungicide, Miticide & Insecticide Concentrate
Ferti-lome Rose, Flower & Vegetable Spray Concentrate
Monterey 70% Neem Oil Fungicide/Insecticide/Miticide
Natural Guard Neem Concentrate
Garden Safe Fungicide 3 Concentrate; & RTU2
Southern Ag Triple Action Neem Oil Concentrate
Propiconazole Banner Maxx Fungicide
Bonide Fung-onil Lawn & Garden Disease Control RTS1
Bonide Infuse Fungicide Concentrate; & RTS1
Ferti-lome Liquid Systemic Fungicide II Concentrate
Sulfur3 Bonide Sulfur Plant Fungicide (also wettable for spray)
Ferti-lome Dusting Sulfur
Hi-Yield Wettable Dusting Sulfur
Safer Brand Garden Fungicide Concentrate; & RTU2
Southern Ag Wettable or Dusting Sulfur
Thiophanate-methyl Cleary’s 3336 WP Turf & Ornamental Fungicide
Southern Ag Thiomyl Systemic Fungicide
1 RTS = Ready to Spray (hose-end applicator)
2 RTU = Ready to Use (pre-mixed spray bottle)
3 Never apply a horticultural oil spray within 2 weeks of a sulfur spray, and do not apply horticultural oils or sulfur when the temperature is above 90 °F or to drought-stressed plants.
With all pesticides, read and follow all label instructions and precautions.

Black Spot On Rose Canes

You have Black spot on your rose canes. It is a fungal disease that affects only roses. It can winter over on infected canes such as yours. Sanitation is the key to keeping it in check. Cut the infected canes back as much as possible and discard in the garbage. In between cuts, sterilize your pruners with either a mixture of 1 part bleach to 9 parts water or wipe the pruners down with rubbing alcohol. Clean up any dead leaves that may be present because they can harbor the fungus . Put down a light layer of mulch such as a shredded hardwood mulch. Do not use rocks of any kind because when it rains, the water will splash up underneath the leaves and spreads the disease. You can apply fungicides as a preventative treatment and may have to apply during the growing season as well. Excellent air circulation is important too so having it in a sunny open spot is ideal. I’ve included a link for more information on Black spot on roses. https://extension.umass.edu/landscape/fact-sheets/black-spot-rose

Identify And Fix Rose Canker Fungus

By Stan V. Griep

American Rose Society Consulting Master Rosarian – Rocky Mountain District

Rose canker is also known as Coniothyrium spp. This is the most common of the several kinds of rose canker fungi that can affect the canes of roses. When left unmanaged, not only can rose cankers eat away at the beauty of your rose bushes, but they can eventually kill your rose plant.

Identifying Rose Canker Fungus

Rose canker is what is known as pathogenic fungi, while it is not really all that complicated a fungus, it can still cause a lot of damage. Rose cankers will often show itself as black splotches on the canes of rose bushes.

Many times after a recent pruning rose stem cankers will show up, especially when the pruners have not been cleaned between the prunings of different rose bushes. Rose canker can spread from a rose bush where it was just pruned out to an uninfected rose bush by using the unclean pruners.

Canker is most active during cold times of the year when rose bushes are less active.

Preventing And Curing Rose Canker

Removal of the infected cane or canes to good clear cane tissue below the canker followed by the spraying of a good fungicide will help in getting rid of or reducing the canker problem. Remember to wipe off the pruners with the disinfectant wipes or dip them in the Clorox solution after each pruning of a diseased cane! Always wipe down your pruners with Clorox or Lysol disinfectant wipes or dip them into a mixture of Clorox and water before pruning each rose bush.

Promoting vigorous growth helps as well, as a healthy thriving rose bush fights off the canker attacks well.

Using a good preventative fungicidal spraying program goes a long way to not having to deal with the frustrations of a fungal infection and the elimination of it. A rotation of fungicidal sprays is recommended to help keep the different funguses from becoming resistant to the fungicides effects.

Prevent and manage rose cankers

Question: I have several pink Knock Out roses that I’ ve had for several years, and they have always been healthy and lovely. I make sure I care for them properly. Recently I noticed that all of them have cankers and discoloration (black and dark brown) up and down the stems. I have done research on this and ha ve been getting mixed messages. Some say it is a fungus that cannot be treated and will eventually kill the plant. Some say a soap insecticide will help. Others say something different. We have had harsh winters before, but I do not recall any as wet as we’ve had this year since I put the roses in. Is that what is causing this? What can I do — if anything?

Answer: Rose cankers are a problematic issue for rose growers, regardless of which types of roses you grow. Though Knock Out roses are far more disease resistant than many other types of roses, they are not immune to rose cankers.

There are four primary canker diseases of roses, including brown canker, common canker, cane blight canker and brand canker. All are caused by pathogenic fungi. Cankers can easily be confused with winter injury. The presence of new cankers during the growing season is a sign that winter injury is not to blame.

The first signs of a canker infection are small, round lesions on the canes. They can be reddish, yellow or near black. The lesions enlarge over time, turning brown with a dark outer edge. They may spread to cover the complete circumference of the stem. When this happens, the entire stem may die.

Infections typically start when the plant is injured through poor pruning, flower harvest, or another tissue-damaging action. It is also easily spread via infected pruning equipment.

If left untreated, a canker infection can spread down into the crown of the rose and cause complete plant death. Unfortunately, infections are more prevalent during wet season such as the one we had last year.

To prevent and manage rose cankers, you must clean your pruning shears with a 10% bleach solution or another disinfectant between each clip because the pathogen is easily spread on “dirty” tools. Prune the plant only when necessary and remove all infected branches and dispose of them in the garbage. Do not put them on the compost pile. When cutting off a branch with a canker, remove all of the stem down to about 2 inches below the lowest canker. Always prune in dry weather.

You can help protect your roses from cankers this coming season by applying an organic biofungicide based on Bacillus subtilis to all sides of all stems every 14 to 21 days throughout the growing season. One common brand name is Serenade. This organic fungicide is useful for preventing cankers, black spot, powdery mildew and other fungal diseases. Insecticides will do nothing to prevent or control rose stem cankers as they are not an insect-caused problem.

  • Horticulturist Jessica Walliser is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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    What is black area on cane of rose?

    This appears to be a canker (Coniothyrium Canker). Cankers are caused by fungi and generally appear as dead areas on canes and vary in color from light tan to dark purplish-brown to black.

    The fungus can enter healthy canes through wounds caused by improper pruning, flower cutting, wind, hail damage, or cultivation injury. It can occur on roses that have been weakened by black spot, poor nutrition or winter injury. Some research has shown that the fungus can enter right after spring pruning if the weather is extremely wet.

    Once the fungus has entered the plant, the canker may grow and eventually girdle the stem causing a dieback of the entire cane. If it reaches the crown of the rose, it will destroy other canes and eventually the plant.

    Canes with cankers must be pruned out. Prune back at least 2-3 inches below the canker to a strongly growing shoot, the next cane below or to the main branching if needed. Before and after each pruning cut, dip the pruners in a disinfectant solution of 70 percent rubbing alcohol, or liquid household bleach (1 part of bleach to 9 parts of water). Disinfect and oil pruners again after use on this diseased plant. Remove and destroy the infected cane immediately.

    Keep roses healthy with proper watering and keep them fertilized to improve vigor. Watch for common rose pests such as thrips, aphids, spider mites, powdery mildew and blackspot and treat accordingly. Avoid any type of injury to canes, and practice proper winterization of roses.

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