Mildew on squash leaves

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Powdery mildew, common on zinnias and other crops in mid-summer, starts with just a few spots on the lower leaves, as shown in this photo. Without treatment, it will spread to shoots and buds and eventually kill the plant.

By Lynn Byczynski

As warm, dry weather settles in this month, be alert for the development of powdery mildew on crops. Powdery mildew is a common summer problem on many types of vegetables and cut flowers. But most powdery mildew can be avoided or cured with inexpensive, homemade remedies that have been proven to work as well as or better than commercial fungicides.
Several species of fungus cause powdery mildew, each affecting different groups of plants. The main species is Erysiphe cichoracearum, which affects composites, including:
•Vegetables – cucurbits, cucumbers, endive, lettuce, melons, parsley, poumpkins, and potatoes.
•Flowers – chrysanthemum, begonia, dahlia, phlox, sunflower and zinnia.
Nine other species of powdery mildew fungus affect cole crops, peas, eggplant, pepper, tomato, strawberries, beans, black-eyed peas, grapes, and tree fruits.
The first thing to know about powdery mildew is that it is quite different from downy mildew, despite some similarities in appearance. Both produce light-colored masses of spores on foliage. Downy mildew develops spores only on the undersides of leaves, whereas powdery mildew will appear on both sides of leaves as well as shoots, buds and sometimes flowers. Moreover, downy mildew is a disease that appears in cool, wet conditions and is generally stopped by warm, dry, windy weather. Powdery mildew thrives when foliage is dry and the weather is warm; wind spreads the spores to other plants. In fact, powdery mildew spores can’t germinate or grow when foliage is wet, so overhead watering is sometimes recommended as a preventative on highly susceptible crops.
Powdery mildew spores overwinter on perennial crops such as grapes, raspberries, strawberries and fruit trees, or in plant debris left from last year. When conditions are just right, this year’s growth can be affected and the disease spreads quickly. The optimum situation for the development of the disease is cool, humid nights followed by hot, dry days.
If left unchecked, powdery mildew will cause leaves to turn yellow, die and fall off, leaving fruits and vegetables exposed to sunburn and making cut flowers unmarketable. Preventative action in susceptible crops and regular scouting can prevent a catastrophic outbreak of this disease. Following are some of the remedies and products available for preventing powdery mildew Some of these recipes may be acceptable for organic production, but you should check with your certifying agency if in doubt. Commercial products should have the approval of OMRI, which can be verified at Much of the advice about how to mix these sprays is from the Bio-Integral Resource Center, whose contact information is at the end of the article.
The newest organic control for powdery mildew is milk. In 1999, Brazilian scientist Wagner Bettiol reported excellent control of the fungus on greenhouse-grown zucchini using fresh cow’s milk diluted with water to a 10% solution. An Australian researcher, Peter Crisp, experimented with milk on roses and wine grapes – which get powdery mildew from different organisms. Crisp found that in most cases the 10% milk solution worked as well as the leading synthetic fungicide and as well as sulfur.
According to an article in Science News, the results have been proven in the field by grape growers. But there is some concern than using any product, even milk, repeatedly may allow the fungal organisms to develop resistance. So the current recommendation is to spray for powdery mildew every week, but alternate between remedies. And there are plenty of other recipes from which to choose.
Baking soda
Sodium bicarbonate – the same stuff you use for making biscuits or deodorizing the refrigerator – is highly effective against powdery mildew. Its effectiveness is not understood precisely, but it is thought to be a case of induced resistance – that is, the baking soda causes the plant to produce some compound to defend itself against pathogens.
Baking soda is particularly effective when paired with a horticultural oil. To mix your own solution, for each gallon of water in your sprayer, add 1 Tablespoon baking soda and 2.5 Tablespoons of horticultural oil. This makes a 0.5% concentration of bicarbonate, the maximum recommended for control of powdery mildew on roses; other species may tolerate greater concentrations, but you should test for phytotoxicity before spraying large areas.
Baking soda has a few drawbacks: First, it must be sprayed every week to protect new growth on the plant. It also can build up in soil when used in drought-stressed areas where only drip irrigation is used. Increased bicarbonate in soil can lead to removal of calcium and magnesium, and prevent the absorption of iron and lead to iron chlorosis. (These risks appear to be small in most farm situations.)
Yet another kitchen remedy is garlic extracts, which can be made by blending two bulbs (not cloves!) of fresh garlic in a quart of water with a few drops of liquid soap. The liquid should be strained through cheesecloth to remove solids and then refrigerated. That concentrate should be diluted 1:10 with water before spraying. That provides a concentration of 25-50 parts per million of the active compound allicin, which will help prevent germination of powdery mildew spores. Once the spores are active, though, a concentration of 300 to 500 ppm is needed to cure powdery mildew.
Compost tea
The antifungal properties of compost tea are by now well known. Many organic growers, especially in the rainy Northwest part of the country, have had great results and are advocates for the benefits of compost tea. Several companies sell equipment for making compost tea, and some growers just mix one part of finished compost with six parts of water and let it soak for a week, then strain and dilute with water until it’s the color of tea.
Oils and anti-transpirants
Oils alone can be used to control powdery mildew. Vegetable seed oils such as canola oil can be used, at a rate of 2.5 to 3 Tablespoons per gallon of water, with the addition of a quarter-teaspoon of liquid soap to emulsify the oil. Most commercial horticultural oils already have an emulsifier added, so additional soap is not needed. Soap itself has been found to control powdery mildew, but it can cause phytotoxicity.
Neem oil is labeled for control of powdery mildew, rust, blackspot, botrytis, downy mildew and other diseases. Spraying with 2.5 Tablespoons per gallon of water every 7 to 14 days is recommended.
Mint oil (Fungastop) and rosemary oil (Sporan) are now being marketed as fungicides. Cinnamaldehyde (Cinnamite) also has been effective at controlling powdery mildew.
Antitranspirants are sprays that are used to prevent water loss from plant foliage. They have been found to also protect against several foliar diseases, including downy mildew, powdery mildew, and blackspot. One study showed that the antitranspirants Wilt Pruf and Vapor Guard, which are widely available at garden centers, protected roses from powdery mildew for 30 days. According to BIRC, antitranspirants are nonspecific against pathogens, so the fungus is not likely to develop resistance. However, they do reduce plant photosynthesis and should be used only during sunny weather and they need to be reapplied to protect new growth.
Copper and sulfur
A traditional treatment for plant diseases involves spraying sulfur and copper on highly susceptible plants. Several products are available for use by organic growers, but they are considered restricted, which means they can only be used if other management practices have failed. Both copper and sulfur can irritate skin and mucous membranes, so breathing protection should be worn.
Bacillus subtilis and Bacillus pumilis are two bacteria that have been found effective against powdery mildew and other diseases. Several commercial products containing these bacteria are now available: Serenade for home gardeners and Rhapsody for commercial growers. Sonata is specifically for control of powdery mildew in roses.

Lynn Byczynski is the founder of Growing for Market magazine and the author of The Flower Farmer: An Organic Grower’s Guide to Raising and Selling Cut Flowers.
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Treatment for White Spots or Powdery Mildew on Cucumber, Squash, Melon and Other Plants

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Powdery mildew and other leaf mildews tend to appear when the humidity and rains come in. It starts out looking like little white powder spots on the top and undersides of your cucumber, zucchini, squash and melon plants. The white spots will grow to cover the enter leaf and spread across the vine. It will also grow on plant stems. You may also see leaf yellow spotting where the fungus is sitting.
Prevention is best. If you know when the fungus arrives in your area… spraying the susceptible crops 2x’s weekly with 1 tablespoons of baking soda to 1 gallon water is best.
If you notice you have the disease, like I do in the video you want to spray a little bit differently as the goal is to kill off the fungus and stop it from spreading or reproducing. I recommend the same strength spray, you should use a quality sprayer, of 1 tablespoon baking soda to 1 gallon of water. I would spray daily for 3 days and then every 2 days for 1 week. After that I would spray 2x’s weekly for prevention.
Remember to spray the tops and bottoms of the leaves. You want to soak them down. The change in PH from the baking soda is what causes the cure. It is also a good idea to remove badly infected leaves.

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How to Manage Pests

Pests in Gardens and Landscapes

Powdery Mildew on Vegetables

Revised 11/08

In this Guideline:

  • Identification and damage
  • Life cycle
  • Management
  • About Pest Notes
  • Publication
  • Glossary

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.


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.

Resistant Varieties

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.

Table 1. Host Plants and Control Measures for Powdery Mildew Species.

Hosts Fungus species Controls
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

Cultural Practices

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.

Fungicide Application

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

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.


McCain, A. H. 1994. Powdery Mildew. HortScript #3, Univ. Calif. Coop. Ext. Marin County.


Pest Notes: Powdery Mildew on Vegetables

UC ANR Publication 7406

Produced by University of California Statewide IPM Program

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Posted by Carol Miller|June 7, 2017

When scouting pumpkin fields that are being sprayed with a protectant fungicide (i.e. chlorothalonil), keep in mind the fungicide is likely protecting the upper leaf surface, so the typical circular white powdery colonies may appear more chlorotic or yellow in color on the upper surface, but will be powdery white on the corresponding lower leaf surface. Photo by Beth K. Gugino.

Welcome to American Vegetable Grower® magazine’s first field scouting guide, this month concentrating on cucurbit powdery mildew. Each month we will bring you a different pest, ranging from weeds, to diseases, to insects, and even wildlife.

We reached out to pathologists to learn how to spot and treat powdery mildew. This month, our contributors are Beth K. Gugino, Penn State University, Debra Inglis, Washington State University, and Anthony Keinath, Clemson University in South Carolina.


Squash Powdery Mildew Basics

Scientific name: There are different strains impacting vegetable growers: Podosphaera xanthii; Golovinomyces cucurbitacearum; Leveillula taurica
Common name: Powdery mildew; squash powdery mildew
Crops affected: All cucurbits are susceptible, although many commercial cultivars have resistance.
Geographical range: Powdery mildew on pumpkin and other cucurbits has a worldwide distribution, including all of the U.S.

The Economic Impact of Powdery Mildew

Powdery mildew can reduce watermelon yields directly by causing the plants to produce fewer fruit, and indirectly by killing leaves that shade the fruit, leading to sunburn. The losses can be up to $1,500 per acre, or 75% of the value of the crop. Powdery mildew also can cause pumpkins to set fewer fruit, delay fruit ripening, and cause the handles to be soft, so they don’t hold up when the fruit are sold.

Cosmetic issues can have an impact as well, with sunscald giving fruit a less than desirable rind color. For pumpkins, handles/stems can be an important factor in purchasing decisions for consumers.

How to ID Powdery Mildew

Gugino: Fortunately, powdery mildew is fairly easy to identify. However, it requires scouting not only the upper leaf surface, but the lower leaf surface, petioles, and crown. Powdery mildew is favored by dense foliage and lower light intensity so the microclimate within the plant canopy is more favorable for disease development. Therefore, powdery mildew tends to first develop on the underside of older leaves within the canopy.

Inglis: Powdery mildew on cucurbit leaves is usually quite distinctive in that symptoms first appear as superficial white spots, which expand into powdery, white masses of fungal mycelium and spores on infected plants. The powdery masses sometimes have tiny, black structures, which are the fruiting bodies of the fungus.

Keinath: Scouts should look for the characteristic powdery white fungus growth on the bottom of the leaf, directly below the yellow spots.

How to Distinguish Powdery Mildew from Other Problems

Inglis: Sometimes powdery mildews are confused with downy mildews. Although the names are similar, downy mildews often produce a gray/brown (not powdery), felt-like growth of spores and mycelium on leaf undersides, and are caused by a different group of plant pathogens. Also, any leaves severely affected by powdery mildew that turn brown and die, might be mistaken for drought stress or Verticillium wilt, but I think in most cases that would be unlikely.

Keinath: The pale yellow spots of powdery mildew on the upper leaf surface can be mistaken for downy mildew or possibly for spider mite damage, although spider mite damage on watermelon normally is a brighter yellow than powdery mildew, and the yellowing is clustered in the center of the leaf.

Cultural Management

Inglis: Planting resistant or tolerant cultivars whenever they are available will help to slow down disease progress. Different races of cucurbit powdery mildews have been identified in some cucurbit growing regions of the U.S., but not in western Washington, thus growers here often need to base their cultivar choices on past experience. Also, using crop rotation, avoiding shading, and not planting dense stands can be useful cultural control measures in addition to fungicide applications.

Keinath: Growers can use resistant cultivars plus organic fungicides, then switch to traditional chemistry if powdery mildew continues to develop.

Known Resistances

Podosphaera xanthii is resistant to azoxystrobin and pyraclostrobin, Keinath says. Resistance to other fungicide active ingredients, such as boscalid and quinoxyfen, has been found in various parts of the eastern U.S., so fungicides with these active ingredients may not work in all areas.

Guginio’s Tips to Get the Most from Fungicides

Fungicides, when combined with host resistance, can be very effective for managing powdery mildew on pumpkin, Gugino says.

Single-site mode-of-action products that are specific for powdery mildew tend to be most effective. Many of these also have translaminar or locally systemic activity, meaning that when they are applied to the upper surface of the leaf they will move through the leaf tissue and protect the underside of the leaf.

The escaped ornamental Verbena bonariensis is also susceptible to Podosphaera xanthii, so if this plant is nearby, and has powdery mildew, spores have been blown into the area. Photo by Frank Wouters

This is in comparison to protectant-type fungicides such as chlorothalonil, which will only protect the plant surface the product was applied to, so adequate coverage is essential. It is important to include protectants in with a powdery mildew fungicide program for resistance management so that the pathogen population is exposed to more than one fungicide active ingredient at a time.

Gugino has been conducting pumpkin powdery mildew product efficacy trials at the Russell E. Larson Research and Education Center in Centre Co., PA, annually since 2009. There are a lot of products registered for managing powdery mildew, so it is very important to pay attention to their Fungicide Resistance Action Committee (FRAC) codes when developing a fungicide program.

She suggests initiating a program with one of the more effective products such as Torino (Gowan Company; FRAC U6), Vivando (BASF; FRAC U8) or Quintec (Dow AgroSciences; FRAC 13) and then rotating them with products that have different modes of action such as Fontelis DuPont; (FRAC 7) or Pristine (BASF; FRAC 11 and 7) or a FRAC 3 fungicide like Procure (Arysta LifeScience) or Tebuconazole (Albaugh), Inspire Super (Syngenta; FRAC 3 and 9) and Aprovia Top (Syngenta; FRAC 7 and 3).

It is important to always read the fungicide label because not all cucurbits are on all labels and the label is the federal law.

Powdery mildew is one of the easier diseases to manage organically on cucurbits and there are a number of options including copper, sulfur, oils like Eco E-rase from IJO Products (jojoba oil), JMS Stylet oil from JMS Flower Farms (paraffinic oil), Trilogy from Certis USA (neem oil) and Organocide from Organic Laboratories (sesame oil), as well as potassium bicarbonate based products such as Kaligreen (Arysta LifeScience)and MilStop (BioWorks) to name a few.

5 Tips to Managing Powdery Mildew

Gugino says there are five things for growers to keep in mind when trying to manage powdery mildew in their pumpkin fields:

  1. Select resistant varieties whenever possible. Host resistance is always the first line of defense.
  2. Before the season begins, have a powdery mildew fungicide program in place. To manage for fungicide resistance, know which products you are going to apply and in what sequence based on the FRAC code numbers. Having this plan in advance means less work during the production season.
  3. Obtaining good fungicide coverage is as important as developing a fungicide spray program. This can be challenging as the crop canopy expands. Use water-sensitive paper within the crop canopy to gain a sense of coverage and adjust/calibrate equipment as needed.
  4. If planting multiple successions, avoid planting down wind of the earlier crop and disk under the crop residue once with harvest to reduce inoculum.
  5. When scouting, scout by variety and keep good field notes on where and when powdery mildew was first observed and how it is progressing during the season. Evaluate your spray program to determine if it is providing adequate disease control.

Carol Miller is Editor of American Vegetable Grower. See all author stories here.

Powdery Mildew Control On Squash: Treating Powdery Mildew In Squash Plants

We had the perfect storm of weather conditions this summer to contribute to a severe infection of powdery mildew on squash, specifically our butternut and spaghetti squash. The squash leaves with mildew died back, exposing the fruit to sunscald at its formative stage. It’s not uncommon for squash leaves to have powdery mildew, but as it affects yield, how can you go about treating powdery mildew in squash? Read on to learn more.

Squash with Powdery Mildew

Powdery mildew spreads rapidly and can travel a long distance. In addition to squash plants, it may afflict any number of veggies, including:

  • Artichokes
  • Cucumbers
  • Eggplant
  • Lettuce
  • Melons
  • Parsnips
  • Peas
  • Radishes
  • Tomatoes
  • Turnips

However, there is a different species of powdery mildew that attacks each different veggie. In the case of cucurbits, there are three different fungal species responsible for causing powdery mildew: Podosphaera xanthii, Golovinomyces cucurbitacearum, and Golovinomyces orontii.

Contrary to what you might think, powdery mildew on squash is not prevalent during wet growing seasons. In fact, moist conditions are not necessary at all to foster this fungus and it quite likes it hot. Hence, the aforementioned “perfect storm” here in the Pacific Northwest; we have had an unusually dry, hot summer.

So how do you identify powdery mildew in squash? This disease is fairly obvious in appearance. It appears on older leaves first, as reddish brown spots. At onset, the disease can only be identified via microscope, but quickly it will become apparent as it rapidly spreads to create white mildew covered leaves, petioles and stems. This powdery mycelium makes the leaves appear to have been dipped in talc. The leaves lose their normal dark green hue, turn pale yellow, then brown and finally shrivel, leaving the squash exposed to sunburn.

Conidia (spores) are rapidly produced in the powdery mycelium and any wind or air movement carries them to adjacent plants and leaves as well as off to plants situated even farther away. In fact, it only takes three to seven days from initial infection to appearance of symptoms. Powdery mildew thrives in dense plantings, shaded to low light exposure and high relative humidity. Infection can occur anywhere between 50-90 F. (10-32 C.), but it favors warmer temps up to 80 F. (26 C.), but not over 100 F. (37 C.). Also, powdery mildew in cucurbits is spread because the disease overwinters and is spread to successive generations of squash.

Powdery Mildew Control

Along with the perfect storm of weather conditions, we no doubt aided and abetted the disease. As mentioned above, the disease overwinters. Practicing a crop rotation will go a long way in preventing the spread of powdery mildew. Do not plant cucurbits in the same area for at least two years. We did not practice crop rotation; I blame my other half.

Additional management techniques for treating powdery mildew in squash are to destroy any diseased plant debris, space plantings since a densely planted plot is more likely to be infected, and plant resistant varieties when possible. Also, keep the garden free of weeds. Powdery mildew control may also be need to be combined with a timely application of a fungicide.

When using fungicides, it’s too late for them to be of any use once symptoms become rampant. Fungicides work by preventing infection of healthy foliage, so find the infection early. There are a number of organic options available as well as traditional fungal sprays.

  • Sulfur and “Stylet” oil are effective products for powdery mildew control.
  • Fixed copper fungicides have also shown results in managing powdery mildew.
  • Neem oil is also an effective combatant for managing powdery mildew.

Whatever you choose, remember the key is early application, before the disease is readily apparent all over the foliage.

How To Get Rid of Mold or Powdery Mildew on Squash or Cucumber Leaves

What Is This Mold or Powdery Mildew?

The other day I was in my garden and I spotted it. Oh the dreaded powdery mold or mildew that no gardener wants to see. How could this have happened?

It has been quite dry this year, but a lot cooler than usual. I am very careful on not watering the leaves, and water at the base of the plant. So why was I getting this mildew or mold on my leaves?

I wish I had a solid answer, but as with any garden experience, it can change from one year to the next.

So many things can play a factor in whether or not problems arise in your garden. The wind, the weather, the rain, insects and birds all can bring mold or mildew to your garden.

What To Do Once A Problem Arises

When a problem does come about, and trust me you will experience problems, then you get to add another notch to becoming an expert gardener. When it comes to gardening you can’t grow as a gardener unless you have challenges to grow from.

Pesky pest and diseases might be a nuisance yes, but trust me when I say you will become a better gardener once you learn how to conquer these problems.

So today we are going to talk a bit about mold or a powdery mildew as shown in the first picture above and how to conquer this problem.

An All Natural Solution

I try my best to keep my garden as organic as possible. So if I can treat a problem without chemicals, I am going to do just that.

Mold or powdery mildew is a gray or white like substance that can be furry or powdery and grows on the leaves. It can grow on the top of the leaf or on the underside. It can spread rather rapidly so it is best to treat it as soon as you notice it.

Todays recipe is so simple and is something everyone has in their kitchen already. What is the magic ingredient you ask?


Yep, you read that right, milk! Milk naturally has proteins that can protect and help kill off any unwanted molds or mildew. I know, who knew right?

Here Is What You Will Need

Yep, it really is this easy! So are your ready to make this solution?

So here is what you are going to need.

  • Get a clean spray bottle.
  • Fill it with 40% milk and 60% water (any milk will do, but I use organic because that is all I have in my kitchen).
  • Shake and use.
  • You also need the sun to make this work.

Yep, it really is that easy!

Lets Do An Example On A Zucchini Plant

Now that you have your solution, head outside on a warm sunny day and spray the areas in question. Be sure that you spray the underside of the leaves as well.

Allow the milk mixture to fully dry in the hot sun. This is a very important part of to making this work. The sun bakes the proteins into the leaf and kills off the unwanted mold or mildew.

Spray liberally. Here is what my plant looked like after I was done spraying. Repeat again in 10 days if needed.

This will work on zucchini, squash, summer squash, winter squash, watermelon, pumpkins and any other gourds you could think of.

A Second Application On A Cucumber Plant

It also works on cucumbers. Lets take a look at this picture below. In this picture is a climbing cucumber plant. You can clearly see the mold starting to form.

I sprayed one application and this is how it looked several days later. Here I am repeating it 10 days later. Not sure it really needed it, but I was being extra cautious.

The plant continued to thrive and look at this amazing cucumber…yep a healthy plant indeed.

Share Your Thoughts

What about you…have you had any issues with how to get rid of mold or powdery mildew on squash and cucumber plants?

Tagged with → caring for plants • cucumbers • gardening problems • mildew • molds • squash • zucchini

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