Milk for powdery mildew

Powdery mildew is becoming a problem on the cucurbits and kale in the campus terrace gardens.

  

Powdery mildew on zucchini leaf

Powdery mildew on kale leaf

The disease is most severe in warm, dry weather with high relative humidity. Young, succulent leaves and plants growing in nitrogen-rich soil are most prone to infection. 

The class observed the most severe infection at the east end of the west terraces, where the squash vines are particularly large and vigorous.

Leaf wetness actually prevents infection. Our recent switch from a sprinkler irrigation system to a drip irrigation system probably made the gardens more susceptible to powdery mildew by eliminating periods of leaf wetness.

Milk can be more effective than commercial fungicides in controlling powdery mildew on cucurbits. The students pruned out infected leaves to remove sources of inoculum and increase air flow through the plants, and then sprayed the remaining leaves with a 40% solution of milk in water. They will continue to spray milk once or twice each week.