I was sent the following pictures by a friend a couple of days ago asking me if I recognized the condition. I didn’t, so she sent the pictures to the Cornell Cooperative Extension Diagnostic Lab which quickly diagnosed it as Angular Leaf Spot, a serious fungal disease that affects the squash family including cucumbers, zucchini, winter squashes (ie. butternut) and melons.

Angular Leaf Spot Late Stage Infection

Angular Leaf Spot Underside of Leaf

Unfortunately, at the advanced stage of the disease, she was advised to remove and destroy the plants, especially since she had some unaffected ones nearby.

The today I was in my garden and saw the following leaves in my garden on my butternut squash.

Angular Leaf Spot Early Infection

Angular Leaf Spot Moderately Serious Infection

It looked a lot like Angular Leaf Spot to me. Because my infection seemed to be less serious than my friend’s, I just pruned off the leaves and I’ll be monitoring the plants closely to see if I caught the infection early enough.

My friend lives an number of miles away from me and since we both seem to have gotten the disease, I imagine it might be fairly common here in the Hudson Valley this year. The large amounts of rain we’ve had this spring are just the right kind of conditions to encourage Angular Leaf Spot.

It’s called Angular Leaf Spot because the lesions formed by the fungus are often stopped at veins in the leaf giving the lesions an angular shape. There are no sure organic chemical controls for Angular Leaf Spot though Copper Sulfate may have some effectiveness.

If you have Angular Leaf Spot make sure that you don’t put any of the infected debris into your compost pile. Dispose of it in your regular trash. And if you do prune off the affected leaves make sure you sterilize your pruners with alcohol, hydrogen peroxide, or flame before using them on anything else.

Hopefully you don’t have this disease, but make sure you keep an eye out for it. Remember being an alert gardener is your best way to control diseases and pests in you organic garden.