My impatiens are wilting

White spots on Impatiens’ leaf tops

The spots (damage) and patterns makes me suspicious of abiotic reason. It is possible that this damage is caused by the fertilization. These “burns” can occur when fertilizer is sprayed on hot days. Or was there other products used at the approximate time prior to these symptoms appearing? Products such as cleaners, fence stains, water from swimming pool, irrigation water (has happened when city water switches to using primarily well sources).
From the photos, it does not appear to be due to a pathogenic cause. Additionally, new growth appears to be normal. I would suggest care in watering and fertilizing – prevent/reduce splashing by applying close to the soil surface. Then monitor the new growth – In the absence of the damage factor, new growth should appear normal.
If damage continues to occur, I would suggest for you to consider submitting a sample for diagnosis to a plant disease diagnostic clinic. For those services in TX, you can check out the Texas Plant Disease Diagnostic Lab at Texas A&M (http://plantclinic.tamu.edu)

Gray Mold – Annuals, Bulbs, Groundcovers, Perennials, and Vines


Gray Mold (Botrytis) on geranium

When a plant or part of the plant (leaf, flower, fruit) rapidly collapses and dies this is called blight. The blight fungus Botrytis cinerea attacks plants in landscapes, especially under cool, wet, overcast or very humid conditions, which cause plant parts to remain wet for extended periods. In all species of Botrytis, the first symptom is a small tan spot or spots that may rapidly enlarge. If the stem is infected, girdling the stem, the shoot will wilt. Botrytis is easily diagnosed by the fluffy gray mold produced on blighted plant parts under moist conditions. Botrytis can rapidly blight flowers. Infected petals that fall onto foliage or stems can cause additional blighting and dieback. Other species of the Botrytis fungus are specialized to attack a more narrow range of plants. B. elliptica attacks lilies, causing leaf spotting that progresses up the plant, blighting leaves, stems, and flowers. B. paeoniae causes bud and shoot blight of herbaceous and tree peonies. B. tulipae causes the disease “tulip fire”, characterized by a rapid spotting and blighting of tulip petals and foliage.


Botrytis on impatiens


Infected tulip


Infected pansy

Management

Deadhead and dispose of old spent and diseased blossoms.

Connecticut State The Connecticut Agricultural Experiment Station

Plant Health Problems
Diseases caused by Fungi:
Rhizoctonia crown rot, Rhizoctonia solani.
Infection first appears as a general decline, yellowing, and wilting of the entire plant. This is usually followed by complete collapse of the plant. Brown to black lesions can often be seen at the base of the stem, usually at the soil line.
Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the crown area of the plant. Adequate spacing between the plants can promote good air circulation. Highly symptomatic plants can be rogued and removed since recovery is unlikely. Control can also be achieved with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are iprodione and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Wilt, Verticillium.
Vascular wilt is a troublesome disease of impatiens, especially in beds that have been planted to impatiens for many years. Plants may be attacked at any stage; young plants can suddenly dry up or older plants might develop a pale green color accompanied by wilting of lower leaves, often first appearing on one side of the plant. This is frequently followed by a general wilting and death of the entire plant. Plants may wilt in the middle of the day and seem to recover at night. When the stem is cut, a black discoloration or streaking may appear in the vascular tissues.
Control of this disease is difficult since the pathogen is commonly found in soil. One of the key strategies for control of vascular wilts is prevention. Therefore, it is important to avoid planting in infested soil. It is also helpful to maximize plant vigor by good cultural care and watering. Careful handling of plants will avoid root injury which enables the fungus to enter the plant. Since repeated use of the same area greatly increases the amount of disease, rotation is essential. When available, it is also helpful to use resistant varieties. Chemical controls are not effective for these fungi.
Leaf spots, Alternaria, Cercospora.
Symptoms first appear as tan to brown to black spots with purple margins and vary with the causal fungus. Spots often appear on lower leaves first and can gradually spread up the plant.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are chlorothalonil, thiophanate-methyl, iprodione, and sulfur. Consult the label for dosage rates and safety precautions.
Powdery mildew, Erysiphe.
White powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot, humid weather. Heavily infected leaves turn brown and shrivel.
Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, potassium bicarbonate, copper sulphate pentahydrate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Botrytis blight, Botrytis cinerea.
Flowers turn a papery brown and become covered with gray, fuzzy masses. Senescing flowers are particularly susceptible. Tan to brown spots with a target-like appearance can also develop on the leaves. These patches are often associated with flowers which have dropped onto the leaf surface. This disease is particularly troublesome during periods of extended cloudy, humid, wet weather.
Good sanitation practices including grooming the plants and removing spent or senescing flowers can minimize the potential for infection. These affected tissues should be carefully removed and discarded when they are dry. It is also important to avoid wetting the flowers when watering and crowding plants. Adequate spacing between the plants can promote good air circulation. Use of fungicides is usually not necessary. However, control can enhanced with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are mancozeb, copper sulphate pentahydrate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Diseases caused by Viruses:
Impatiens necrotic spot and Tomato spotted wilt, viruses (INSV and TSWV).
These diseases are the most important problems on impatiens and can be extremely damaging. They are particularly troublesome on double-flowering varieties. Symptoms can appear as black ringspots, mosaics, and necrotic spots with tan centers and brown margins. Petals can develop a color breaking and leaves can pucker, become distorted, yellow, and abscise. Stems occasionally develop distinctly black areas or lesions and plants can be stunted. These pathogens are transmitted by the western flower thrips.
Control of these diseases is focused on prevention since once plants are infected, they cannot be cured. It is important to eliminate and remove infected plants as soon as they are recognized and to eliminate other symptomatic plants since these viruses have very broad host ranges. It is also critical to manage the thrips population.
Diseases caused by Nematodes:
Root-knot nematodes, Meloidogyne spp.
Plants appear unthrifty, small, and weak. Above-ground symptoms are nonspecific as plants appear stunted, yellowed, and wilted. Diagnostic symptoms can be observed by the presence of galls on the roots. These can range in size from small swellings to large, distinctly clubby galls. The northern root-knot nematode, M. hapla, is a sedentary endoparasite, meaning that it infects host roots after hatching from eggs, stimulating the formation of a small gall containing specialized feeding cells, and feeds in the same location through several molts to produce several hundred offspring. Because most of its life cycle is inside roots, it may be spread to new locations with vegetative propagation material. This nematode is parthenogenetic, a single female can reproduce without males, resulting in a new generation every 28 days under ideal conditions. The galls produced on roots interrupt translocation and act as a nutrient sink. The nematode has a wide host range, but a number of ornamentals, including Rudbeckia, Aster, and others, have been shown to be resistant.
Control of this disease is very difficult since these nematodes have a wide host range. Growing resistant plants or rotating to small grains can greatly reduce or eliminate nematode populations in infested soil.
Diseases caused by Physiological/Environmental Factors:
Dodder, Cuscuta spp.
This parasitic seed plant is recognized by the presence of yellowish-orange strands which wrap around the plants like masses of spaghetti. Because dodder is a leafless plant which does not contain chlorophyll and therefore cannot manufacture its own food, it sends haustoria or sinkers into stems and leaves of the impatiens in order to obtain nutrients. Flower clusters are visible on the strands in midsummer.
Control of this plant parasite is extremely difficult. It is very important to rogue and remove any plants with symptoms as soon as possible after they are detected and especially before the dodder develops flowers. If dodder has been a problem in a particular planting bed, it is helpful to avoid planting in that area for several years.
Insect Problems:
Balsam aphid, Macrosiphum impatientis.
This aphid can be a problem on impatiens and balsam. Control is seldom needed.

Western flower thrips, Frankliniella occidentalis.
This insect can be an important problem in greenhouses because it transmits tomato spotted wilt virus. When needed, insecticidal soap, registered for use against this pest in Connecticut, can be used to suppress thrips populations. Control with organophosphate, carbamate, or pyrethroid insecticides may be difficult due to insecticide resistance. Options appropriate for commercial growers include abamectin (restricted use) or spinosad. Consult the label for dosage rates and safety precautions.

Downy mildew of impatiens

What is it?

Symptoms include dense or sparse sporulation on underside of leaves

Downy mildew of Impatiens species and cultivars was detected for the first time in Australia in 2006. The disease is caused by the fungus Plasmopara obducens. It can cause stunting, premature leaf fall, poor flowering and in some cases even complete collapse and death. It has previously been found in North America, Asia and Europe.

Significance to Australia

Symptoms include mottled leaves

In England and the USA, recent outbreaks in 2003/04 have been very damaging and have caused losses of up to 80-90%. These were associated with the introduction of planting material from Central America. In the USA, epidemics of the disease are reported to be explosive, destructive and costly. The disease was detected in Victoria in October 2006 and losses have been similar to reports from overseas. Impatiens represent around 10% of the bedding plant sector in Australia. The disease has subsequently been found in New South Wales and Queensland.

Where did it come from?

Symptoms include plants with few or no flowers

The entry pathway of the Victorian detection is not known. The disease can be spread over relatively short distances by water splash and wind, but long distance dispersal is likely to occur via infected or contaminated planting material and possibly seed. As the disease can remain latent for significant periods of time after infection, it may have been introduced on apparently healthy material which only showed symptoms following favourable conditions.

Symptoms

Yellowing, stunting and premature leaf fall on a tray of bedding impatiens.

The first symptoms are usually pale green leaves. The underside of affected leaves may show a sparse or dense white layer covering the entire leaf surface. Affected leaves then yellow and may fall prematurely, or they may collapse. Plants can be stunted and produce small pale leaves, with few or no flower production. Early symptoms of downy mildew infection may be difficult to detect as the characteristic white downy growth is restricted to the underside of leaves, and leaf symptoms may be confused with nutritional deficiencies or mite damage.

Spread

Few distinct symptoms of downy mildew of impatiens

Spread over short distances is via water splash and over longer distances by air currents. The pathogen can be spread over long distances through movement of infected cuttings and plants before any symptoms have appeared. Similarly, some reports indicate that the pathogen can survive in seed, which, when sown, produces systemically infected plants. Such plants may have a long latent period before symptoms are seen.

Management

Management should include:

  • disease exclusion
  • monitoring for disease symptoms
  • hygiene
  • cultural practices especially humidity control
  • fungicide treatments.

Hosts

The host range apparently includes only cultivated and wild species of impatiens. In Victoria the, disease has been found in both single and double flowered commercial types. Overseas records indicate that I. walleriana, I. balsamina and I. noli-tangere are hosts. There are also unconfirmed reports that New Guinea hybrids (Impatiens x hawkeri) are hosts.

Lane CR et al (2005) First report of Impatiens downy mildew (Plasmopara obducens ) in the UK. Plant Pathology 54, 243.

To report suspected exotic or unusual pests or diseases, call the EXOTIC PLANT PEST HOTLINE 1800 084 881

by Heather Faubert

Impatiens downy mildew has changed our view of impatiens (Impatiens walleriana). I think no impatiens should be planted in the Northeast, or anywhere, except in very arid locations such as the Midwest. I heard of many landscapers replacing customers’ impatiens at the landscapers’ expense, once the plants succumbed to downy mildew in 2012. Don’t let this happen to you in 2013.

Impatiens downy mildew may look like white down on the underside of primarily yellow Impatiens leaves, but can also be found on the underside of green leaves. Photo courtesy Tina Smith, UMass Extension.

Impatiens downy mildew, caused by Plasmopara obducens, attacked many New England gardens in 2012. In 2011, the disease was first seen in landscapes in eleven states including Massachusetts and New York. In 2012, impatiens downy mildew was found in 33 states including all New England states. On Long Island, near where it was found in 2011, diseased plants were found in early June, 2012.

Impatiens walleriana are susceptible to downy mildew. Photo courtesy Tina Smith, UMass Extension.

This disease affects all Impatiens walleriana plants (garden impatiens, double impatiens, mini-impatiens, and the I. walleriana interspecific hybrids Fusion® and Butterfly® impatiens), as well as I. balsamina (commonly known balsam impatiens). It does not attack New Guinea impatiens, Impatiens hawkeri.

Signs of Disease

Downy mildew symptoms typically start with a few yellow or off color leaves that become completely yellow over time. Green or yellow leaves may also curl downward. Infected young plants will be stunted, while mature plants drop leaves and flowers with only a few small leaves remaining on bare stems. A white, downy-like growth may be visible on the underside of infected leaves under cool temperatures (about 60 to 73F) and moist or humid conditions. The white growth is actually spores which can be blown or splashed around and cause more infections.

Only four hours of leaf wetness are needed to initiate new infections. The time from infection to the appearance of symptoms varies from about five to 14 days depending on the age of plant tissue, temperature and humidity. Due to this latency period, infected plants can be shipped and planted without showing any disease symptoms.

Infected plants suffer from early leaf drop. Photo courtesy Tina Smith, UMass Extension.

Impatiens downy mildew is here to stay because it overwinters as oospores and also infects our native jewelweed, I. capensis, though so far, symptoms have been mild. Also, many uninformed gardeners will probably plant impatiens this spring, so there will be plenty of Impatiens walleriana plants to infect and spread the disease.

Let’s see this disease as an opportunity for landscapers to educate their customers and the public and not contribute to the problem!

For more information, refer to:

About the Author

Heather Faubert is a Research Assistant at University of Rhode Island Greenhouse. She may be reached at [email protected]

Editor’s Note: Consider substituting the following annuals in beds that previously held impatiens, or try out a combination of perennials that will bloom throughout the growing season.

Annuals:
Begonias
Torenia
Coleus
Caladiums
Lobelia

Perennials:
Spring blooming – wild blue phlox, tiarella, yellow wood poppy, wild geranium
Summer blooming – downy skullcap, great blue lobelia, black cohosh, cardinal flower
Fall blooming – white wood aster, heart leafed aster, wreath goldenrod

Or peruse the plant lists offered by these institutions:

Plant Health Problems
New Guinea impatiens are susceptible to the same diseases as impatiens. See Impatiens for a detailed discussion of these problems.
Diseases caused by Viruses:
Impatiens necrotic spot and Tomato spotted wilt, viruses (INSV and TSWV).
These diseases are the most important problems on impatiens and can be extremely damaging. They are particularly troublesome on double-flowering varieties. Symptoms can appear as black ringspots, mosaics, and necrotic spots with tan centers and brown margins. Petals can develop a color breaking and leaves can pucker, become distorted, yellow, and abscise. Stems occasionally develop distinctly black areas or lesions and plants can be stunted. These pathogens are transmitted by the western flower thrips.
Control of these diseases is focused on prevention since once plants are infected, they cannot be cured. It is important to eliminate and remove infected plants as soon as they are recognized and to eliminate other symptomatic plants since these viruses have very broad host ranges. It is also critical to manage the thrips population.
Diseases caused by Physiological/Environmental Factors:
Sunburn, environmental.
When planted in full sun, many cultivars of New Guinea impatiens develop a marginal necrosis or brown patches on the leaves.
This disease is generally not very serious and can be avoided by not planting susceptible cultivars in full sun.
Insect Problems:
See Impatiens.

What’s Wrong with My Impatiens?

Recently a number of Long Islanders have come to Hicks with questions about their impatiens. They mention that the leaves of the plants are yellowing and the undersides have developed a white, downy-like color. These are classic symptoms of downy mildew, a water mold that affects impatiens walleriana and has no known cure.

As a leader in the garden center industry on Long Island, we stopped selling impatiens walleriana several years ago. We continue to feel it is our responsibility to help stop the spread of downy mildew by instead offering alternative annual plants that will thrive in your Long Island garden.

If you purchased impatiens walleriana at another nursery and think your impatiens have been affected by downy mildew, here is what you need to know:

What is it?
Downy mildew is a devastating disease that can spread by air and by the ‘splashing’ of spores due to rain and overhead watering. It is prevalent across the country and can come from any number of places.

Impatiens before downy mildew appears.

What are the symptoms?
Early symptoms include yellowing or stippling of the leaves or a white, downy-like color on the underside of the leaves as well as stunting of growth. Advanced symptoms include a grayish, fuzzy substance on leaves and stems. Leaf and flower drop will eventually result in bare, leafless stems.

Impatiens infected with downy mildew.

How did I get it?
Downy mildew is a water mold. The disease spreads most commonly when the foliage stays wet for extended periods of time and there are cool night temperatures and moist conditions. Therefore areas of deep shade, beds that receive overhead watering and densely planted beds are more highly susceptible to downy mildew.

What do I do now?
Once the disease is identified remove all of the plants and plant debris (leaves, flowers, etc.) from soil and containers. Spores can overwinter in the plant debris so the removal is imperative to help limit future spread. It is not recommended to plant impatiens in that location for several years. Chemical treatments are not recommended as most are ineffective.

What about New Guinea Impatiens?
Downy mildew only affects impatiens walleriana. New Guinea impatiens have proven to be highly tolerant to the disease.

What else can I plant?
There are many other beautiful flowering plants that thrive in shade. Take a look at our handout “Great Annuals to Replace Impatiens” for additional information.

What next?
At Hicks Nurseries we continue to follow the research of Cornell Cooperative Extension and various test gardens. If you have any questions about downy mildew please stop by the nursery*, call us at 516-334-0066, email us at [email protected] or reach out to us on Facebook or Twitter. Our number one goal is to help you be successful so that you may enjoy your garden for many years to come.

*If you would like to bring a sample of your impatiens to the store for closer inspection, please place your sample in a sealed plastic bag and bring it to the Garden Care Information Desk.

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