White Pumpkin Leaves: How To Get Rid Of Powdery Mildew On Pumpkins
Do you have a white powdery mildew on your pumpkin leaves? You’re in good company; so do I. What causes white pumpkin leaves and how can you get rid of that powdery mildew on your pumpkins? Keep reading to find out more about treating powdery mildew on pumpkin plants.
What Causes White Pumpkin Leaves?
The reason we have a powdery mildew on our pumpkin leaves is because it is caused by a leaf infecting disease that is very common. The name is, in fact, “powdery mildew” and is given to a group of diseases caused by related fungi.
Each one has a different host, but they all share the same appearance – a grayish-white, powdery carpet that can be seen on leaves, stems and flowers. Unlike other fungal diseases, powdery mildew thrives in warm conditions and does not require moisture to grow.
How to Get Rid of Powdery Mildew on Pumpkins
While powdery mildew on pumpkins looks unpleasant, the good news is that a mild case isn’t fatal. That said, if left untreated, the disease will likely spread. Powdery mildew first appears as white, powdery spots. These spots gradually spread and a pumpkin that is severely affected may have a reduced yield, shorter growth time and pumpkins with little flavor. Before learning about treating powdery mildew on pumpkins, it’s a good idea to learn a little about its life cycle.
In the spring, fungi begin to produce spores, which are then dispersed into the air. When they contact an appropriate host and conditions are suitable, they infect the plant. The initial white spots continue to expand and join as the infection progresses. The fungus overwinters on plant debris and then when the weather warms over 60 degrees F. (16 C.), the cycle starts all over again.
Although powdery mildew doesn’t require watery conditions to germinate, high humidity is a factor. High humidity fosters spore formation. Temperatures between 60-80 F. (15-26 C.), shade, and high humidity are premium conditions for powdery mildew.
If the powdery mildew on the pumpkins seems to be minimal, remove the infected leaves, vines, or blossoms. Depending upon when the infection set in, this may give the plant enough time to complete production of its pumpkins. If conditions are still favorable for the growth of powdery mildew, it will likely reappear again.
Cucurbits, like pumpkins, are highly susceptible to this disease. Plant them in full sun, allow for good air circulation, and avoid excess fertilizer to try and thwart the disease. Use a slow release fertilizer. It is likely that they will need an application of fungicide, however.
Fungicides fall into the categories of protectants, eradicants or both. There are two oils that work best as eradicants but have some protectant quality as well – neem oil and jojoba oil. Other horticultural oil brands may be used as well. Don’t spray within 2 weeks of a sulfur spray or when temps are above 90 degrees F. (32 C.).
Sulfur has been used for centuries to manage powdery mildew in pumpkins and other cucurbits but must be used BEFORE disease symptoms appear. Don’t apply sulfur when it is near or over 90 degrees F. (32 C.) on within 2 weeks of an oil spray.
Lastly, you can try a biological fungicide (Serenade), which contains beneficial microorganisms that destroy fungal pathogens. It is nontoxic to people and pets and kills the powdery mildew pathogen, but isn’t as effective as oil or sulfur.
How to Manage Pests
Powdery Mildew on Vegetables
Powdery mildew on melon leaves.
Sugar pea foliage damaged by powdery mildew, Erysiphe polygoni.
Powdery mildew causes irregular yellow blotches on tomato leaves.
Brownish spots on pea pod from powdery mildew infection.
Powdery mildew is a common disease on many types of plants. There are many different species of powdery mildew fungi (e.g., Erysiphe spp., Sphaerotheca spp.) and each species only attacks specific plants. A wide variety of vegetable crops are affected by powdery mildews, including artichoke, beans, beets, carrot, cucumber, eggplant, lettuce, melons, parsnips, peas, peppers, pumpkins, radicchio, radishes, squash, tomatillo, tomatoes, and turnips. Powdery mildews generally do not require moist conditions to establish and grow, and normally do well under warm conditions thus they are more prevalent than many other leaf-infecting diseases under California’s dry summer conditions.
IDENTIFICATION AND DAMAGE
Powdery mildew first appears as white, powdery spots that may form on both surfaces of leaves, on shoots, and sometimes on flowers and fruit. These spots gradually spread over a large area of the leaves and stems. An exception is one of the powdery mildews that affects artichokes, onions, peppers, and tomatoes: it produces yellow patches on leaves but little powdery growth.
Leaves infected with powdery mildew may gradually turn completely yellow, die, and fall off, which may expose fruit to sunburn. On some plants, powdery mildew may cause the leaves to twist, buckle, or otherwise distort. Powdery mildew fungal growth does not usually grow on vegetable fruits, although pea pods may get brownish spots. Severely infected plants may have reduced yields, shortened production times, and fruit that has little flavor.
All powdery mildew fungi require living plant tissue to grow. Year-round availability of crop or weed hosts is important for the survival of some powdery mildew fungi. Special resting spores are produced, allowing overwinter survival of the species that causes the disease in cucurbits, lettuce, peas, and certain other crops.
Most powdery mildew fungi grow as thin layers of mycelium (fungal tissue) on the surface of the affected plant part. Spores, which are the primary means of dispersal, make up the bulk of the white, powdery growth visible on the plant’s surface and are produced in chains that can be seen with a hand lens in contrast, spores of downy mildew grow on branched stalks that look like tiny trees.
Powdery mildew spores are carried by wind to new hosts. Although humidity requirements for germination vary, all powdery mildew species can germinate and infect in the absence of free water. In fact, spores of some powdery mildew fungi are killed and germination is inhibited by water on plant surfaces for extended periods. Moderate temperatures (60° to 80°F) and shady conditions generally are the most favorable for powdery mildew development. Spores and fungal growth are sensitive to extreme heat (above 90°F) and direct sunlight.
The best method of control is prevention. Planting resistant vegetable varieties when available, or avoiding the most susceptible varieties, planting in the full sun, and following good cultural practices will adequately control powdery mildew in many cases (Table 1). However, very susceptible vegetables such as cucurbits (cucumber, melons, squash, and pumpkins) may require fungicide treatment. Several least-toxic fungicides are available but must be applied no later than the first sign of disease.
In some cases, varieties resistant to powdery mildew may be available. If available, plant resistant varieties of cantaloupe, cole crops, cucumber, melons, peas, pumpkins, and squash. If you plant more susceptible varieties, you may need to take control measures.
|cucumbers, endive, lettuce, melons, potato, pumpkin, squash||Erysiphe cichoracearum||resistant varieties of lettuce, cucumber water sprays fungicides if necessary on squash and pumpkin|
|broccoli, Brussels sprouts, cauliflower, and other cole crops radicchio, radishes, turnips||Erysiphe cruciferarum||not usually required|
|tomatoes||Erysiphe lycopersici||fungicides if necessary|
|peas||Erysiphe pisi||resistant varieties sprinkler irrigation|
|carrots, parsley, parsnips||Erysiphe heraclei||tolerant varieties|
|beets||Erysiphe polygoni||tolerant varieties|
|artichoke, eggplant, peppers, tomatillo, tomatoes||Leveillula taurica||rarely required fungicides if necessary|
|beans, black-eyed peas, cucurbits, okra||Sphaerotheca fuliginea||resistant varieties for some fungicides if necessary|
Plant in sunny areas as much as possible, provide good air circulation, and avoid applying excess fertilizer. A good alternative is to use a slow-release fertilizer. Overhead sprinkling may help reduce powdery mildew because spores are washed off the plant. However, overhead sprinklers are not usually recommended as a control method in vegetables because their use may contribute to other pest problems.
In some situations, especially in the production of susceptible cucurbits, fungicides may be needed. Fungicides function as protectants, eradicants, or both. A protectant fungicide prevents new infections from occurring whereas an eradicant can kill an existing infection. Apply protectant fungicides to highly susceptible plants before the disease appears. Use eradicants at the earliest signs of the disease. Once mildew growth is extensive, control with any fungicide becomes more difficult. The products listed here are for home garden use. Commercial growers should consult the UC Pest Management Guidelines.
Several least-toxic fungicides are available, including horticultural oils, neem oil, jojoba oil, sulfur, and the biological fungicide Serenade. With the exception of the oils, these materials are primarily preventive. Oils work best as eradicants but also have some protectant activity.
To eradicate mild to moderate powdery mildew infections, use a horticultural oil such as Saf-T-Side Spray Oil, Sunspray Ultra-Fine Spray Oil, or one of the plant-based oils such as neem oil or jojoba oil (e.g., E-rase). Be careful, however, to never apply an oil spray within 2 weeks of a sulfur spray or plants may be injured. Also, oils should never be applied when temperatures are above 90°F or to drought-stressed plants. Some plants may be more sensitive than others, however, and the interval required between sulfur and oil sprays may be even longer always consult the fungicide label for any special precautions.
Sulfur products have been used to manage powdery mildew for centuries but are only effective when applied before disease symptoms appear. The best sulfur products to use for powdery mildew control in gardens are wettable sulfurs that are specially formulated with surfactants similar to those in dishwashing detergent (e.g., Safer Garden Fungicide) However, sulfur can be damaging to some squash and melon varieties. To avoid injuring any plant, do not apply sulfur when air temperature is near or over 90°F and do not apply it within 2 weeks of an oil spray. Other sulfur products, such as sulfur dust, are much more difficult to use, irritating to skin and eyes, and limited in terms of the plants they can safely be used on. Copper is also available to control powdery mildew but is not very effective.
Biological fungicides (such as Serenade) are commercially available beneficial microorganisms formulated into a product that, when sprayed on the plant, destroys fungal pathogens. The active ingredient in Serenade is a bacterium, Bacillus subtilis, that helps prevent the powdery mildew from infecting the plant. While this product functions to kill the powdery mildew organism and is nontoxic to people, pets, and beneficial insects, it has not proven to be as effective as the oils or sulfur in controlling this disease.
How to Use
Apply protectant fungicides, such as wettable sulfur, to susceptible plants before or in the earliest stages of disease development. The protectant fungicides are only effective on contact, so applications must provide thorough coverage of all susceptible plant parts. As plants grow and produce new tissue, additional applications may be necessary at 7- to 10-day intervals as long as conditions are conducive to disease growth.
If mild to moderate powdery mildew symptoms are present, the horticultural oils and plant-based oils such as neem oil and jojoba oil can be used to reduce or eliminate the infection.
Gubler, W. D., and D. J. Hirschfelt. 1992. Powdery Mildew. In Grape Pest Management. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3343. pp 57-63.
McCain, A. H. 1994. Powdery Mildew. HortScript #3, Univ. Calif. Coop. Ext. Marin County.
Pest Notes: Powdery Mildew on Vegetables
Authors: R. M. Davis, Plant Pathology, UC Davis W. D. Gubler, Plant Pathology, UC Davis S. T. Koike, UC Cooperative Extension, Monterey County
Produced by University of California Statewide IPM Program
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Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2019 The Regents of the University of California. All rights reserved.
For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.
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How to Identify Powdery Mildew Damage
- Plants infected with powdery mildew look as if they have been dusted with flour.
- Powdery mildew usually starts off as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit.
- Powdery mildew usually covers the upper part of the leaves, but may grow on the undersides as well.
- Young foliage is most susceptible to damage. Leaves turn yellow and dry out.
- The fungus might cause some leaves to twist, break, or become disfigured.
- The white spots of powdery mildew will spread to cover most of the leaves or affected areas.
- The leaves, buds, and growing tips will become disfigured as well. These symptoms usually appear late in the growing season.
Powdery mildew first appears as small white spots on the upper part of the leaves. Photo Credit: The Regents of the University of California, UC Davis.
Powdery Mildew In Pumpkins - What To Do For Powdery Mildew On Pumpkin Leaves - garden
MANAGING POWDERY MILDEW IN PUMPKIN WITH RESISTANT VARIETIES
Margaret Tuttle McGrath and Jane F. Davey
Department of Plant Pathology, Cornell University
Long Island Horticultural Research and Extension Center
3059 Sound Avenue, Riverhead, NY 11901-1098. [email protected]
Bob Precheur, Mac Riedel, Andy Wyenandt, Jim Jasinski, and Celeste Welty
Dept. of Horticulture and Crop Science, Departments of Plant Pathology Southwest Extension IPM, and Entomology, Ohio State University, Columbus, OH 43210-1087
Timothy E. Elkner
Penn State Cooperative Extension
1383 Arcadia Rd., Rm. 1, Lancaster, PA 17601-3184
Walter R. Stevenson and R. Vaughan James
Plant Pathology Department, University of Wisconsin
1630 Linded Drive, Madison, WI 53706-1520
Mark Hutton and David Handley
University of Maine Cooperative Extension
P.O. Box 179, Highmoor Farm, Monmouth, Maine 04259
Powdery mildew is a common disease of pumpkin, as well as other cucurbit crops, which reduces yield when not adequately managed. The characteristic white, powdery fungal growth is readily recognizable on foliage. Infected leaves usually wither and die. Premature loss of leaves can result in reduced market quality because fruit ripening prematurely before achieving full color and handles may be shriveled or rotten. Size and/or number of fruit can be reduced when powdery mildew is severe. Severe disease can also lead to imperfections on fruit rind such as speckling and oedema. In addition, powdery mildew infection predisposes plants to other diseases, in particular, gummy stem blight/black rot.
Resistant varieties are becoming an increasingly important tool for managing powdery mildew in pumpkin as the number of resistant varieties available to growers increases and as fungicide resistance continues to challenge effective chemical control. The first powdery mildew resistant (PMR) pumpkins, Merlin and Magic Lantern, were commercialized in 1998 and the next, Mystic Plus, in 2000. Recently, several new PMR varieties of pumpkin, as well as winter squash, have been released each year. Effectively managing powdery mildew with fungicides necessitates products able to provide control on the underside of leaves through systemic, translaminar or volatile activity. Unfortunately, all such materials have been at risk for resistance development. Strains of the powdery mildew fungus resistant to QoI fungicides (FRAC Group 11 aka strobilurins Amistar, Quadris, Cabrio, and Flint) are believed to now occur throughout the US. Resistance to MBC fungicides (aka benzimidazoles Topsin M and Benlate) are likely still widespread in the US. They were common on Long Island in 2004. QoI and MBC resistances are qualitative, thus resistant strains are fully insensitive to these fungicides. Resistance to the DMI (demethylation inhibiting) fungicides (Bayleton, Nova, and Procure) is quantitative pathogen strains exhibit a range in fungicide sensitivity depending on the number of genetic changes they possess that affect the fungicide’s ability to function. Moderately resistant strains likely are common in the US now. These are fully insensitive to Bayleton and have reduced sensitivity to low rates of Nova and Procure.
PMR pumpkin varieties vary in their susceptibility to powdery mildew depending on the number of genes for resistance they possess. The major gene for resistance in PMR varieties was obtained from a wild cucurbit at the Cornell Department of Plant Breeding. Varieties with this resistant gene from both parents (homozygous) usually develop less powdery mildew than those with resistance from one parent (heterozygous). In catalogues these are often, but not always, described as resistant and tolerant, respectively. The degree of powdery mildew suppression in PMR pumpkins and squashes usually is not as great as that in PMR melons and cucumbers. Some heterozygous PMR pumpkin varieties exhibit suppression of powdery mildew development for a few weeks, but become as severely affected as a variety without resistance by the end of the season. However, although leaves become severely affected by powdery mildew on these PMR varieties, they typically have less mildew on fruit handles than susceptible varieties. Also, initial disease suppression results in leaves dieing later and consequently more fruit with good color and solid handles at harvest. In addition to the major PMR gene, there are modifying genes with small affects that could account for the variation in susceptibility observed among PMR varieties. The resistance in PMR pumpkins and winter squash is not race-specific as it is in melons. However, the powdery mildew fungus has the potential to evolve the ability to overcome this specific major resistance gene in PMR pumpkins and squash. Such a new strain of the pathogen would be called a race.
To obtain information growers need on relative tolerance and yield to select PMR varieties most suitable for their operation, evaluations have been conducted in ME, NY, OH, PA, and WI over the past 3 years. Pumpkins were either transplanted or direct-seeded into black plastic mulch or bareground in June. Cultural practices recommended for each area were followed. Fungicides for powdery mildew were applied to achieve an integrated management program except in WI. Powdery mildew developed naturally. Severity was assessed repeatedly. Other diseases were also assessed in some locations. Fruit number, weight and quality were determined. References to full reports on the individual studies are listed at the end.
Among the 39 PMR varieties and experimental lines evaluated, powdery mildew was least severe on Gold Dust, Bumpkin, Touch of Autumn, Hobbit, Magician, Gladiator, and experimental lines from pumpkin breeding programs at Outstanding Seed Company, Harris Moran Seed Company, Cornell University and University of New Hampshire. Relative to varieties without PMR genes, percent control achieved with PMR pumpkins ranged tremendously – from 0% (eg no control) to 100% (complete control) (Table 1).
Variation was detected in susceptibility to other diseases among the varieties and experimental lines evaluated. Super Herc (HMX 3692), Gold Gem, Gold Medal, and Pro Gold 510 were highly susceptible to anthracnose while Wee-B-Little was highly resistant in the Ohio State pumpkin variety trial in 2003. Magic Lantern and Merlin were shown in another project to be more susceptible to bacterial wilt than the susceptible varieties Harvest Moon and Howden (*). Research is underway to determine if this occurs with other resistant varieties.
Average fruit weight of the PMR varieties and experimental lines evaluated ranged from 0.5 to 26.5 (Table 2). Additional information about yield can be found in the full reports on these experiments (web sites listed below). Some reports also have descriptions of horticultural characteristics and photographs. Harris Moran pumpkins generally had good color and appearance. In the NY 2004 experiment, fruit of 03RPX764 was the most popular among growers and others who selected their top 3, Scarecrow was second, and Sorcerer was third. Other pumpkins receiving high ratings were Howden, Magic Lantern, Magician, and HMX 2689.
An integrated program, consisting of a reduced fungicide program applied to a PMR variety, is recommended for managing powdery mildew in pumpkin to improve control and to minimize chance of selection of pathogen races able to overcome the genetic resistance in the plant or the action of fungicides. Fewer fungicide applications are needed with a PMR variety because powdery mildew often starts to develop later in PMR than susceptible varieties and the spray interval can be increased from 7 to 14 days without affecting control. Routine scouting is needed when growing PMR varieties not only to determine when powdery mildew has started to develop, and thus fungicide treatment is warranted, but also to detect other diseases. Some fungicides used for powdery mildew on susceptible varieties have broad-spectrum activity and thus will control additional diseases that may consequently not be detected when growing susceptible varieties.
Table 1 : Percent control of powdery mildew on leaves achieved in pumpkin varieties and experimental lines with resistance to powdery mildew relative to varieties lacking resistance in experiments conducted in ME, NY, OH, PA, and WI in 2003, 2004 and 2005 listed in order of overall performance.
Pumpkin Variety or Experimental Line
Percent Control of Powdery Mildew x
CONDITIONS FOR INFECTION:
Free water is not necessary for powdery mildew to infect the plants. Free water may turn out to be destructive for it by killing the spores of these fungal pathogens. So it attacks the plants easily in dry and warm condition without free water.
- It requires considerable humidity to germinate the spores.
- The higher the humidity rate, the higher the germination rate.
- It infects mostly at night in higher humidity.
- 70-80°F is considerably moderate temperate for powdery mildew. So it affects highly at this temperature.
- High temperature difference between day and night helps it to foster.
- Late spring and fall is the perfect time for it to affect in many region.
- High wind also increases the spread of spores.
Other Relative Conditions:
- Crowded plants have poor airflow and damp condition. So they are more susceptible to this disease.
- Stressed and physically weak plants are susceptible too.
Making your own Powdery Mildew Treatment
If powdery mildew does take hold on your plants, there are a number of chemical treatments available. While these fungicides are effective, many people dislike using the potentially harmful chemicals. Organic treatments are also widely available. That said, making your own chemical-free powdery mildew treatment is quick and cost-effective.
This may sound like a surprising solution, but milk is an extremely effective powdery mildew treatment. A 2009 study by the University of Connecticut concluded that milk is just as effective than chemical applications (if not moreso) when it comes to treating powdery mildew. Apparently, milk’s fungal-killing potential comes from the way it reacts to the sun, producing free radicals that are toxic to the fungus.
To make up a milk treatment, mix a solution 60 parts water with 40 parts milk (or whey). Spray this solution onto the affected plants biweekly. If the infection is particularly strong try applying undiluted milk. This will be more potent and should clear up any stubborn infections.
Alternatively dilute 1oz of powdered milk into 2 liters of water. This should be sprayed onto the affected plants once every two weeks until the infection has gone.
2. Bicarbonate Soda Sprays
One of the most effective treatments is spraying affected plants with a bicarbonate solution. To make your own solution, mix 1 teaspoon of baking soda (potassium bicarbonate), with 1 quart of water. Stir the solution, making sure that it is thoroughly mixed. The solution can then be sprayed all over the plant. No need to worry: it’ll only kill the fungus, and won’t harm the plant in any way.
An alternative method is to mix up a solution of 3 tbsp of potassium bicarbonate, 3 tbsp of vegetable oil, and half a teaspoon of castile soap (like fragrance-free Dr. Bronner’s) into a gallon of water. Spray this solution over the affected plant.
Potassium bicarbonate is a safe, effective fungicide that can kill all spores on contact. You can also apply it as a preventative treatment. It works by slightly raising the pH level to above 8.3. This creates a slightly alkaline environment that fungal diseases dislike. You can also use baking powder solutions as a preventative application because they work in a similar way.
Garlic is naturally high in sulfur, and is an effective powdery mildew treatment. To make a fungus-killing solution, crush 6 cloves of garlic and mix with 1 ounce of an organic oil, and one ounce of rubbing alcohol. Allow this mixture to set for 2 days.
Once set, strain the mixture, retaining both the liquid and the crushed garlic. Soak the crushed garlic in a cup of water.
Strain the water and dispose of the crushed garlic. Measure out one gallon of water and add to it the oil and alcohol mixture. Add the garlic water and mix thoroughly. Spray this solution onto the leaves of your plant.
To save time, you can purchase garlic oil and mix it with water to create a solution.
4. Neem Oil
Neem oil is an extremely potent fungal treatment that’s capable of killing an infection within 24 hours. It originates in the seeds of the neem tree, and disrupts the plant’s metabolism, preventing the spores from reproducing. This oil is also an effective insecticide. You can apply it as a treatment, or as a preventative measure to keep your plants healthy.
To make up a neem oil solution, mix 3tbsp of oil in one gallon of water. Spray this solution onto your affected plants once a week until the infection has gone. Be careful not to overly spray the leaves, as this can lead to sunburn. As a result, apply the solution in the evening or as the sun is fading to prevent any burning. Don’t apply neem oil to a plant’s buds or the flowers.
Another effective powdery mildew treatment is acetic acid, which is present in vinegar. In fact, acetic acid has been used to treat fungal infections in human since the time of the ancient Egyptians. Needless to say, it’s also an extremely effective treatment for plants.
Mix 4 tbsp of vinegar with one gallon of water. This creates a 5% solution that you can apply to diseased plants every 3 days. This may seem weak, but a mix that’s overly acidic can burn leaves, doing more harm than good.
Since it’s formulated to kill germs, ethanol-based mouthwash can also eliminate powdery mildew spores. Mix a solution of one part mouthwash to three parts water and spray over affected leaves.
7. Compost Tea
Many organic gardeners like to brew their own compost tea. This solution is prized for its anti-fungal properties, and is growing in popularity amongst many growers.
This mildew can be a frustrating, and often stubborn, problem to deal with. Fortunately, by adopting good gardening practices and using the ideas in this article, you’ll be able to protect your plants from its harmful effects.
About Elizabeth Jones
Elizabeth Jones is a freelance writer and editor from Cardiff, South Wales. Currently specializing in gardening articles, Elizabeth also regularly writes about history, folklore, and genealogy. When not creating interesting content she enjoys gardening, photography, reading and watching sport.