Cucurbit Alternaria Leaf Blight

Cucurbit Alternaria leaf blight is a fungal disease of cucurbits caused by Alternaria cucumerina. Cucurbit crops include watermelon, cantaloupe, cucumber, zucchini, pumpkin, and winter squashes. This pathogen causes brown lesions on the leaves that can develop concentric, target-like rings and a yellow surrounding halo. Fruit can experience sunscald from leaf loss, as well as reduced yield. A. cucumerina survives on infected soil-bound plant debris, spreading via wind, splashing water, workers, equipment, or insects.

Favorable conditions include warm temperatures and high moisture. Cultural management options include rotating away from susceptible crops, maximizing distances between susceptible cucurbit fields, avoiding overhead irrigation and working in wet conditions, and destroying or tilling under infected crop residue. Appropriately-timed fungicide applications can also prevent disease progression.

Cucurbit (squash, cucumber, melon, etc) leaf showing symptoms of Alternaria leaf blight. Photo credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, via Bugwood.org