What Is Powdery Mildew?

Curcurbit family plant leaves wilted and dying? Plants covered in powder and stringy white floss? Could be powdery mildew. Find out more

What is it?

Powdery mildew in the curcurbit family plants is the product of one of two fungi, either sphaerotheca fulginea or the fungi known as erysiphe cicoraceearum. These two fungi primarily infect the leaves and stems on curcurbit family plants such as cucumbers, muskmelons, pumpkins, summer sqaush, winter squash and watermelon plants. Both the fungi sphaerotheca fulginea or the fungi known as erysiphe cicoraceearum can cause damage which can result in the death of the curcurbit plant.

What does it look like?

Sphaerotheca fulginea and erysiphe cicoraceearum damage shows up at first as mottled and powdery yellowish leaves which have wilted. The edges of the leaves may distorted, curled under or stunted as if growth has been interrupted. Often the leaves will recoup from the wilting process during the night when moisture is heavy in the air, but come morning they will wilt and shrivel once again in the sun. This process leads to eventual death of the plant. To confirm powdery mildew you can cut look for signs of powdery growth and strings of cotton candy like floss connecting damaged and mottled leaves. Fruits may become covered with a similar growth and there may be a whitish looking powder covering the curcurbit family plants from stem to leaf, including fruits if damage is severe.

How does it manifest?

The powdery patches and stringy floss like areas on the curcurbit family plants are caused by the fungus. These are patches of fungal spores and strands. These powdery mildew spores are then spread to nearby plants which would otherwise have been healthy by wind and rain. Spores may also be picked up on clothing, gardening tools and insects which then carry the powdery mildew infection to other neighboring curcurbit plants. Both sphaerotheca fulginea and the fungi known as erysiphe cicoraceearum act on the curcurbit family plants in the same manner by sapping the plants of nutrients they need to survive. This causes the yellowing and mottling of the plants. Both fungi thrive in humid as well as dry weather and if your curcurbit plants are closely placed, they can all become infected within a matter of days or weeks as the fungi spores are spread.

What can you do about it?

Curcurbit family plants which show signs of powdery mildew damage may be treated with chlorothalonil containing fungicides as soon as damage is noted. Treatments should be reapplied at seven day intervals until the disease is no longer manifest. If plants becomes reinfected they will need to be treated again with seven day interval applications of chlorothalonil. Additionally, to avoid powdery mildew all together you may wish to seek out and plant varieties which are resisitant to the disease.

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