Powdery mildew can be a real problem in the vegetable garden, especially for cucurbits such as cucumbers, squash, melons and pumpkins. Powdery mildew is a fungus that forms as a white or gray powder on the leaves of plants causing the leaves to become deformed and die. It is far more probable in areas that are damp, are somewhat shady, and have higher levels of humidity.

It is difficult to control powdery mildew once it begins spreading on the plant leaves. This makes it very important to use proactive measures in your vegetable garden to prevent powdery mildew from forming if you've had powdery mildew issues in the past. Here are some ways to prevent powdery mildew from overtaking your cucurbits.

Steps For Preventing Powdery Mildew On Cucurbits

Here are some general guidelines you should follow in your vegetable garden to help prevent powdery mildew.
    • Select curcubits that are powdery mildew resistant, like the ones listed below:
      • Cucumber: 'Diva'
      • Yellow Summer Squash: 'Success', 'Sunray', 'Sunglo'
      • Zucchini: 'Ambassador', 'Wildcat'
      • Pumpkin: '18 Karat Gold', 'Gladiator'

    • Plant cucurbits in full sunlight. The powdery mildew spores have a difficult time surviving in direct sunlight.
    • Provide plants with sufficient spacing. Cucurbits need proper spacing to increase air circulation and to help prevent powdery mildew spores from spreading from one plant to the next.
    • Disinfect any tools after working around cucurbits. If you use a tool around summer squash, for instance, disinfect the tool before working around cucumbers. If the tool isn't disinfected properly the powdery mildew spores could mistakenly be passed from one plant to the other. Disinfect tools with full strength vinegar or a solution of one part bleach to nine parts water.
    • Avoid watering cucurbits in the evening. Allowing the leaves to remain damp over night can increase the likelihood of powdery mildew. Water plants in the morning so the leaves have a chance to dry out before dusk. It is better to water the soil around the plants and avoid getting the leaves wet.
    • If leaves begin showing signs of powdery mildew ( small white or gray spots on leaves) remove the infected leaves from the plant and discard in trash. It is not recommended to place infected leaves in a compost pile.

Homemade Sprays Containing Milk and Baking Soda

One of the simplest and most cost effective ways of preventing and controlling powdery mildew is using a spray of milk and baking soda, applied directly to the top and bottom sides of the plant leaves. The baking soda will increase the pH levels on the leaf surface which will make it difficult for the fungi spores to survive.

It is unclear how the milk actually affects the powdery mildew spores, but spraying milk on infected plant leaves with a solution of nine parts water to one part milk has shown to decrease powdery mildew by 90%. It has been reported that milk can boost the plant's immune system, which also helps to fight powdery mildew and other diseases.

I have used a solution of milk, baking soda, and liquid dish detergent to effectively control powdery mildew in my own vegetable garden. Here is the spray recipe I use:
    • Fill the bottle with 1/2 quart of milk (I typically use skim milk, but any milk will work)
    • Add 3 teaspoons of baking soda
    • Add one drop of liquid dish detergent
    • Mix contents well
    • Reattach bottle to sprayer. Attach sprayer to water hose and spray the top and bottom sides of infected leaves
    • Reapply solution once a week
If you typically have issues with powdery mildew on your cucurbits, I think it is important to begin treatments using the milk and baking soda sprays before the powdery mildew sets in. Using the spray before the symptoms of powdery mildew are seen is critical in preventing it from forming in your vegetable garden.

How do you prevent powdery mildew on your cucumbers, squash and melons? Please share your powdery mildew controls with us!