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What is Powdery Mildew?
That dry white fungus — commonly known as powdery mildew — on your pumpkin plants is caused by an organism called Podosphaera xanthii. Plants are resistant to powdery mildew until they begin to set fruit, and in many cases infestations doesn't appear until late in the season.
Powdery mildew affects all plants in the cucurbit family — which includes pumpkins, gourds, cucumbers, melons, summer and winter squashes, and watermelon — so if you discover powdery mildew on pumpkins, keep an eye out on other plants in the same family.
The first sign of powdery mildew begins with small white lesions on both the top and underside of the pumpkin's leaves. Over the course of several days, the fungus spreads, and leaves quickly wilt, turn brown, and die.
On the bright side, it's believed that the fungus doesn't reside in the soil, but is blown in from southern states (in the United States at least) in the summertime. This means that, even if you've had powdery mildew infestations in the past, you aren't necessarily doomed to suffer it in the future.
Image: powdery mildew. ©Pollinator at the English language Wikipedia. Licensed under the Creative Commons Attribution ShareAlike 3.0 License
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How to Treat Powdery Mildew Using Organic Methods
To successfully kill powdery mildew on pumpkin leaves, act at the earliest signs of infection. There are many approved organic treatments for white fungus, but the one with the greatest reported success also happens to be the simplest: a solution of milk and water, sprayed on the leaves.
Here's how to make your own milk solution to treat powdery mildew on pumpkins.
Milk Solution to Treat Powdery Mildew
In a spray bottle, mix:
1 part milk (whole, 2%, or skim milk will all kill the fungus)
1 part tap water
Treat your pumpkin plants at dusk only — wetting plants during the day can result in leaves getting baked by the hot sun.
Spray both the top and the undersides of the leaves, as both are affected by the powdery mildew.
Spray pumpkins infected with powdery mildew every 3 to 4 days until the white fungus is gone. You may also spray uninfected pumpkins with the milk and water solution every 7 to 10 days as a preventative measure.
The milk spray is the best treatment for powdery mildew, but other organic methods you may try are sulfur-based fungicides, available commercially, and a baking soda solution. The baking soda spray is 1 teaspoon baking soda to 1 quart of water, plus a few drops of liquid dish soap. The soap acts as "glue," allowing the baking soda to adhere to the leaf.
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How to Prevent Powdery Mildew From Affecting Your Pumpkin Leaves in the Future
When it comes to powdery mildew on pumpkins, prevention is your best defense. The fungal infection, once established is pernicious and difficult to eradicate, so it's important to do everything you can to keep your pumpkins from getting infected in the first place. Here are a few tips for keeping pumpkin plants healthy.
Powdery mildew thrives in moist, close environments. Space plants out so they receive adequate air circulation, and when watering, water close to the ground and avoid wetting the leaves. Prune affected areas from infected pumpkins and remove the debris from the garden.
If these tips don't work, an organic treatment such as the milk solution above will help to kill powdery mildew on pumpkin leaves and hopefully save your plants. Have you tried this treatment yourself? Let us know your experiences using a milk solution to treat powdery mildew on pumpkins by leaving a comment below.