Zucchini White Leaf Diseases

Zucchini, a member of the squash family, can develop several distinctive diseases that cause the plant's leaves to appear white in some areas. The afflictions are generally either bacterial or fungal in nature. All of these diseases will affect the fruit, so if there is a treatment available it's best to apply it to the plant as quickly as possible.

Plectosporium blight is a destructive fungal disease that is frequently found in New England. Cool, rainy weather often causes the condition to flare up. The first symptom of plectosporium blight generally is when small, white lesions form on the plant's stem and leaves. The lesions multiply and join until the entirety of the stem and leaves turn white and the plant collapses. The lesions also often spread to the fruit, making the zucchini inedible. To control this disease, apply chlorothalonil and strobilurin fungicides to the zucchini plant.

Angular leaf spot is a bacterial disease that occurs during cold, wet seasons. It first appears on zucchini plants as angular, water-soaked spots on the leaves. As bacteria oozes from the spots onto the leaves, it dries and leaves behind a coating of white residue. The spots will sometimes fall away from the plant, creating holes in the leaves. Spots on the fruit are circular and small. There are chemical herbicide blends that are specially formulated to treat angular leaf spot. Most should be available at your local garden center.

Powdery mildew first manifests itself as round, white spots on the leaves. As the spots spread, they eventually take over the leaves. The tops of the leaves will appear as though they're coated in a white, powdery layer. Eventually, the leaves and stems will turn brown, shrivel and die and the fruit will ripen prematurely and become sunburned. You can apply fungicides to the plant to kill the powdery mildew. Consult the experts at your local garden center to find out the type of fungicide that works best in your area.