Powdery Cucurbit Mildew Control: Treating Powdery Mildew On Cucurbits

Powdery Cucurbit Mildew Control: Treating Powdery Mildew On Cucurbits

By: Mary Ellen Ellis

Cucurbit powdery mildew is a fungal infection with a couple of culprits. It affects any type of cucurbit, but is less common in melons and cucumbers. The characteristic white, powdery mold is pretty easy to spot, but management and prevention of the disease requires several steps.

About Powdery Mildew on Cucurbits

Powdery mildew that infects cucurbit is caused by one of two fungal species: more commonly Erysiphe cichoracearum and less commonly Sphaerotheca fuliginea. While any kind of cucurbit could be susceptible to these fungi, most varieties of cucumbers and watermelons are now resistant.

Unlike some other types of fungal infections on plants, powdery mildew does not require standing water. The most favorable conditions for an infection are medium-high humidity and temperatures between 68 and 80 degrees Fahrenheit (20 to 27 Celsius). The infection is also more likely when foliage is dense and little light penetrates through the leaves.

Cucurbits with powdery mildew can be identified by a white powdery substance on the leaves and stems. The infection will likely begin on leaves that are shaded and on older leaves, so check these for earlier signs of mildew. In some cases, you may see the powder on fruit as they develop.

Powdery Cucurbit Mildew Control Methods

In commercial growing, this disease has been known to reduce harvests by up to 50 percent. There are steps you can take to avoid this kind of destruction in your garden so you don’t have to sacrifice half your cucumbers, pumpkins, squash, and melons.

Start with resistant varieties if you can find them. Melons and cucumbers that resist powdery mildew are common enough. Space your plants out adequately to prevent leaves from being shaded and becoming susceptible to infection. Spacing will also keep humidity around plants lower.

Keep your garden clean by regularly removing plant debris and weeds that could spread the fungus. Crop rotation does not help control this disease because the fungus doesn’t survive in the soil.

Fungicides to control cucurbit powdery mildew are not usually necessary for home gardeners. But, if you have a bad infection, find an appropriate chemical at your local nursery or extension office. To control powdery mildew, these are typically applied early to treat and prevent further spread of the disease.

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Powdery Mildew

Pathogens: Sphaerotheca fuliginea (=Podosphaera xanthii) and Erysiphe cichoracearum (=Golovinomyces cichoracearum)

(Reviewed 12/09 , updated 6/12, pesticides updated 5/16 )

Symptoms and Signs

All cucurbits are susceptible to powdery mildew, but the disease is less common on watermelon than on other cucurbits. Powdery mildew first appears as pale yellow spots on stems, petioles, and leaves. These spots enlarge as the white, fluffy mycelium grows over plant surfaces and produces spores, which give the lesions a powdery appearance. Affected leaves become dull, chlorotic, and may show some degree of wilting in the afternoon heat eventually they become brown and papery.

Comments on the Disease

Powdery mildew of cucurbits may occur at any time in coastal and desert production areas but is more common in fall in the San Joaquin Valley and Sacramento Valley. The disease may be caused by one of two species of mildew fungi, although E. cichoracearum is rare. Several races of each fungus also exist. The pathogens generally overwinter on weeds and their spores can be carried long distances by air currents. Infection is favored by high humidity (50 to 90%), and disease development is favored by vigorous plant growth and moderate temperatures.


Plant resistant varieties, follow good sanitation practices, and control weeds. Start monitoring for powdery mildew during the vegetative growth stage and continue through fruit development. Carefully monitor even those fields with powdery mildew resistant varieties, because there is evidence that plant resistance-breaking races are present in California. Strains resistant to strobilurins (group 11) have already been found throughout the state. If multiple fungicide applications are needed to control powdery mildew, alternate materials with different modes of action especially if using fungicides with medium to high resistance potential (azoxystrobin [Quadris], myclobutanil [Rally], pyraclostrobin [Cabrio], pyraclostrobin/boscalid [Pristine], trifloxystrobin [Flint,] and trifumizole [Procure]). Apply a treatment when disease symptoms first occur and repeat if symptoms reappear.


UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445


R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier

Acknowledgment for contributions to Diseases:

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2017 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 Protect Cucumber Plants From Powdery Mildew

Mildew forms best in cool, wet conditions.

The longer plants are around excess moisture and lower temperatures, the more likely it is that they can develop the ailment.

Plant In A Sunny Location

For starters, always plant your cucumbers in a location that receives at least 8 hours of full sun.

If morning dew is unable to dry off, it sets the stage for mildew.

The sun provides more than just the warmth plants need. It also allows leaves and vines to dry off from early morning dew.

The faster vines and foliage dry in the early cool morning, the less likely it is for mildew to start.

Avoid Watering At Night – Preventing Powdery Mildew

As with many vegetable plants, watering cucumbers at night can increase the risk of issues.

Watering at night keeps heavy moisture around the stems and leaves at the worst time possible – when temperatures are cooler.

Watering plants early in the morning is the best time of all. This allows the plants to quickly dry off as the sun rises, and day time temperature heat up.

Watering at night can provide the perfect conditions for mildew to flourish.

And when you do water, keep from spraying the entire plant with a stream of water.

Instead, water right at or near the root zones of the plants. This keeps the foliage from becoming overly saturated for extended periods.

Providing A Mulch Or Soil Cover For Plants

Mulching or covering the soil below your plants is an excellent way to help prevent a whole slew of issues for cucumber plants – including mildew.

Mulch helps to keep the soil temperatures regulated from the high heat of the day, and the low temps at night.

Landscape fabric allow water to get to roots, and keeps plants from directly touching the soil.

It also keeps the foliage and vines of plants from directly touching the soil, which can make it hard for plants to dry out, and make them more susceptible to soil borne diseases.

Using a landscape cloth or fabric under plants can also provide much of the same protection, and allows water to drain through and away from leaves.

If All Else Fails…

Sometimes, cool and wet spring weather makes it impossible to prevent the onset of powdery mildew.

The first line of defense is to remove and destroy leaves that show the first signs of the tell-tale white spots. Removing them quickly can help keep the fungus from spreading.

Be sure to discard the leaves and keep them clear of the compost pile to avoid spreading the spores.

Using Milk Spray To Combat Powdery Mildew

If you are looking for an all-natural solution, good old-fashioned milk can help.

A 50-50 solution of milk and water sprayed onto the leaves can help keep the disease at bay.

A 50% solution of milk and water applied to the plant’s foliage once a week, or after a heavy rain can help prevent onset of the disease.

Begin applying once the first few leaves begin to form on plants in early spring, and continue until early summer.

For more on growing cucumbers, check out our article : 6 Great Tips For Growing A Banner Crop Of Cucumbers.

Here is to keeping your cucumber plants healthy and strong this year!

This Is My Garden is a garden website created by gardeners, publishing two articles every week, 52 weeks a year. This article may contain affiliate links.

Management Measures for Important Diseases of Pumpkin in the Home Garden

Controlling important diseases of pumpkin in the home garden begins with planting disease-tolerant varieties and using good cultural practices. New pumpkin varieties are released annually which are tolerant to diseases such as Powdery mildew and Fusarium fruit rot. Whenever possible, chose varieties which have tolerance to serious diseases.

Proper crop rotation is essential for reducing the chances of developing soil-borne diseases in pumpkin plantings. Pumpkin and other cucurbit crops should never be planted in the same area of the garden year-to-year and/or should never follow each other. Diseases which affect pumpkin will also affect other cucurbits such as zucchini, melon, cucumber, yellow summer squash, and winter squash. Allow at least 3 to 4 years in soils between pumpkin plantings if possible, to reduce diseases such as Fusarium fruit rot, White speck, Phytophthora blight and White mold. The longer soils are rotated out of pumpkins and other cucurbit crops, the better chances are for reducing soil-borne diseases. Always plant pumpkins in a well-drained soil. Water-logged soils are ideal places for diseases such as Phytophthora blight to develop. Mulching the soil with straw, hay or leaf litter at a 6-inch depth may help to reduce soil-borne disease such as Phytophthora and Fusarium fruit rot by preventing the fruit from coming into direct contact with the soil surface. Mulches may also help to reduce weed pressure and conserve soil moisture during the growing season.

For foliar diseases such as Powdery mildew, Anthracnose, Angular leaf spot, Choanephora, and Downy mildew, make sure plant spacings are wide enough to allow for good air circulation. A tight planting will create microclimates within the canopy, which can favor disease development. Avoid overhead watering at all costs. Overhead watering will create conditions which are favorable for disease development and help spread common diseases. If possible, use a soaker hose or drip irrigation to water plantings. This will ensure that foliage will remain dry. If you have to overhead water, make sure it is done in the morning to allow for adequate drying during the daytime.

Mature fruit should be removed from the garden as soon as it is ready. Leaving fruit in the garden can lead to Sunscald injury during warm days in the early fall, especially if fields have been defoliated by foliar diseases. Ripe fruit left in the garden also can be exposed to late season diseases such as White mold and Fusarium fruit rot or late season heavy frosts, which can shorten the longevity of the fruit.

Fungicide applications can be made to help suppress diseases such as Powdery mildew, Downy mildew, Anthracnose, and White speck. For the above diseases use a fungicide which contains the active ingredient known as chorothalonil, commonly sold in local garden centers and stores. Fixed copper is another chemical which can be used to help suppress bacterial diseases such as Angular leaf spot. To control Bacterial wilt, it is essential that striped and spotted cucumber beetles are controlled early in the growing season as seedlings emerge. Use a labeled insecticide spray or dust. When using any pesticide, always read and follow the label. Row covers can also be placed over newly emerging seedlings, which can keep insect pests such as beetles and aphids from feeding on young plants.

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Watch the video: Powdery Mildew Treatment with Milk Spray

Common name Amount per acre REI‡ PHI‡
(Example trade name) (hours) (days)
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees, and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
(Torino) 3.4 oz 4 0
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Phenyl-acetamide (U6)
(Quintec) 4–6 fl oz 12 3
COMMENTS: Registered for use on melons, including cantaloupe and watermelon. Not effective if disease is established. Do not apply more than 24 fl oz/acre per season.
(Procure 480SC) 4–8 fl oz 12 0
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Demethylation inhibitor (3)
COMMENTS: Do not apply more than 40 fl oz of Procure 480SC/acre per season.
(Rally 40WSP) 2.5–5 oz 24 0
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Demethylation inhibitor (3)
COMMENTS: Do not apply more than 1.5 lb/acre per season.
(Luna Sensation) 4.0–7.6 fl oz 12 0
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Succinate dehydrogenase inhibitor (7) and quinone outside inhibitor (11)
COMMENTS: For use in watermelons only.
(Pristine) 12.5–18.5 oz 12 0
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Quinone outside inhibitor (11) and succinate dehydrogenase inhibitor (7)
COMMENTS: Do not make more than one application before alternating to a fungicide with a different mode of action other than Group 11.
(Fontelis) 12–16 fl oz 12 1
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Succinate dehydrogenase inhibitor (7)
(Microthiol) Label rates 24 0
MODE-OF-ACTION GROUP NAME (NUMBER 1 ): Multi-site contact (M2)
COMMENTS: Sulfur can injure plants, especially when temperatures reach 95°F. Do not use on sulfur-sensitive varieties.
(Kaligreen) 2.5–5 lb 4 1
MODE-OF-ACTION (NUMBER 1 ) An inorganic salt. (NC)
COMMENTS: Use the higher rate when disease pressure is severe. Direct contact with the fungus is required for control. Conditionally allowed in an organically certified crop check with your certifier.
(Cinnacure) 0.25–1 gal 4 0
MODE OF ACTION: A botanical fungicide.
COMMENTS: Make no more than two consecutive applications before rotating to a fungicide with a different mode of action. May not provide good control under all conditions.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number for fungicides with other group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number.
# Acceptable for use on organically grown produce.