White spots on under side of pumpkin leaves

Asked July 20, 2018, 8:39 AM EDT

Can you help me determine the cause of these white spots? I have been fighting cucumber beetles in my garden (mostly on cucumbers but spilling over to pumpkins). Is this bug damage or the beginning of powdery mildew or another disease? Looking to save my pumpkins!

Anne Arundel County Maryland

1 Response

This appears to be powdery mildew. It is favored by warm, wet weather but can also spread under dry conditions. It is especially prevalent in dense canopies and low lying areas whee air circulation is limited.

Once symptoms are visible, it cannot be cured with the types of fungicides available to home gardeners. Commercial growers spray fungicides regularly during the growing season to combat this, and other, diseases. Fungicides sprayed earlier in the season may have prevented/slowed the disease. However, all leaves (both surfaces) have to be protected. This is not easy with pumpkin plants using the types of large droplet sprayers home gardeners typically use.

Hopefully your pumpkin plant will make it through. Next year, consider planting a variety with powdery mildew resistance. jt