White spots on zucchini leaves

Asked June 13, 2013, 5:55 PM EDT

What is the best application to stop the mildew on the zucchini leaves. Losts of rain and muggie days.

Mahoning County Ohio

1 Response

Hi-

Most likely this is powdery mildew on the leaves. Does it look like someone sprinkled baby powder on the leaves? This disease occurs in very humid, moist and warm environments where there is little or no air circulation.

If it is indeed powdery mildew, my first thoughts go to the location of the plant (wide open and sunny), distance between it and other plants (air circulation) and watering practices (water early in the morning, only at the root zone and only using slow, deep watering so as to feed the roots, but to also minimize moisture in the surrounding environment.) If you do not have these, try these practices first. You can also remove a few leaves if these practices do not help. Removing a few leaves will also help improve air circulation.

Here are some great photos of all of the diseases:
http://www.extension.umn.edu/gardeninfo/diagnostics/vegetable/summersquash/leavesspots.html

Besides the cultural practices I mention above (also detailed in this factsheet below), the only other option is fungicides. Details are here:
http://umaine.edu/ipm/ipddl/publications/5085e/

Good luck!