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Powdery Mildew

Powdery Mildew

Podosphaera and Erysiphe species

Fungal

One of the most common and recognizable garden diseases, powdery mildew looks like a dusting of white powder or talc on leaves and stems. It turns up on squash, cucumbers, melons, beans, peas, and many flowers, usually in the second half of summer. Most plants tolerate a light case, but heavy infections weaken the plant and cut the size and quality of the harvest.

🔎 How to spot it

Look for pale yellow spots that quickly develop into round white powdery patches on the upper and lower leaf surfaces, petioles, and stems. The patches spread and merge until whole leaves take on a dull white cast, then yellow, shrivel, and die. Older, lower, shaded leaves are infected first. Unlike downy mildew, the white growth wipes off and appears on both sides of the leaf.

🥀 Damage it causes

Heavy infection weakens the plant, and fruit ripens prematurely and unevenly. Plants set fewer and smaller fruit of lower quality, with poorer flavor and storage life. When leaf cover is lost, exposed fruit is prone to sunscald. Powdery mildew rarely kills a plant outright but can end its productive season early.

🔬 What causes it

Powdery mildew is caused by several closely related fungi, most often Podosphaera and Erysiphe species, that are fairly host specific. Unlike most leaf diseases it does not need wet leaves to infect, and it thrives on warm days around 68 to 81 F with high humidity but dry foliage. Crowded plantings, shade, poor air movement, and excess nitrogen all increase risk. Wind carries the spores from leaf to leaf.

🛡️ Prevent it

Plant resistant or partially resistant varieties whenever you can. Give plants full sun and space them well, and stake or trellis vining crops so air moves freely and leaves dry quickly. Pull weeds that crowd the bed. Avoid heavy nitrogen fertilizer, which pushes soft, susceptible growth. Scout the lower leaves weekly from midsummer so you catch the first patches early.

🧯 If it is already here

Pinch off and destroy the first infected leaves. At the earliest sign, apply an approved organic fungicide such as sulfur, neem oil, or a potassium bicarbonate product, coating both leaf surfaces and repeating per the label; do not use sulfur within two weeks of an oil spray or in high heat. Homemade sprays of one part milk to nine parts water also give some suppression. Remove badly infected plants at season end and do not compost them.

💡 Good to know

Powdery mildew fungi are highly host specific, so the species on your squash will not move to your roses. It often appears like clockwork in mid to late summer as nights lengthen and dews grow heavy. Because each fungus is adapted to its host, rotating crop families and cleaning up debris both help break the cycle.

🌱 Plants it affects

714 plants in the library can be affected by this problem

Acorn SquashAdirondack Blue PotatoAdzuki BeanAfrican Blue BasilAfrican MarigoldAgapanthusAgeratumAgrimonyAji Amarillo Pepper🍓Albion StrawberryAlice du Pont Mandevilla🥔All Blue PotatoAlmondAloe VeraAmbrosia CornAmerican BasswoodAmerican Beauty Dragon FruitAmerican BeechAmerican PersimmonAmethyst Falls WisteriaAmish Paste TomatoAnaheim PepperAnemoneAngelique TulipAngeloniaAniseAnise HyssopAnjou PearAnnabelle Smooth HydrangeaAnnual VincaApeldoorn TulipApple MintApril Tryst CamelliaArbequina OliveArizona Sun Blanket FlowerArkin CarambolaArmenian CucumberAroniaArp RosemaryArugulaAshwagandhaAsian PearAsian PersimmonAtemoyaAtlantic Giant Pumpkin🥕Atomic Red CarrotAucubaAugust Beauty GardeniaAunt Molly's Ground CherryAutumn Joy SedumAvocadoBachelor's ButtonBalsam FirBalsam PoplarBanana PepperBarbara Karst BougainvilleaBartlett PearBay LaurelBayberryBeach PlumBeauregard Sweet PotatoBecky Shasta DaisyBee Balm🍅Beefmaster TomatoBenarys Giant ZinniaBengal Tiger CannaBetter Boy Tomato🥬Bibb Lettuce🍅Big Beef TomatoBig Boy TomatoBilberryBing CherryBitter MelonBlack BeanBlack Beauty EggplantBlack Beauty ZucchiniBlack Beluga LentilBlack Cherry TomatoBlack CrowberryBlack Currant🍉Black Diamond WatermelonBlack Kabouli ChickpeaBlack Krim TomatoBlack RaspberryBlack Sapote🥬Black Seeded Simpson Lettuce🥕Black Spanish RadishBlack Tartarian CherryBlack WalnutBlack-Eyed PeaBlack-eyed Susan VineBlood OrangeBloomsdale SpinachBlue Bird DelphiniumBlue Bird Rose of SharonBlue FescueBlue Lake Green BeanBluecrop BlueberryBocking 14 ComfreyBok Choy

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.