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Cornell Plant Disease Clinic




Helene R. Dillard,Professor, Dept. of Plant Pathology and Plant Microbe Biology and Director of Cornell Cooperative Extension, Cornell University

Phytophthora blight is a devastating disease caused by the water mold Phytophthora capsici.  It is well known throughout the United States as a pathogen on solanaceous (bell pepper, hot pepper, eggplant, tomato) and cucurbit crops (cantaloupe, cucumber, gourd, honeydew melon, pumpkin, muskmelon, summer squash, watermelon, winter squash, zucchini), and in recent years has caused problems on snap and lima beans.  Phytophthora blight was reported on lima beans in 2000 on crops grown in Delaware, Maryland, and New Jersey.  In 2003, the disease was reported on snap beans in Michigan, and in 2008 on snap beans grown on Long Island.  In 2009, a Phytophthora blight epidemic struck snap beans fields in Connecticut, resulting in devastating losses.

Phytophthora blight symptoms on snap beans are as follows:  P. capsici produces large water soaked lesions on the leaves, and as the disease progresses the infected leaves fall off the plant.  Lesions on the stems are brown with white powdery areas.  White lesions are produced on the pods, and infected areas shrivel and desiccate.  Consumed pods are dry, shriveled and leathery.  As the name suggests, this water mold thrives in moist environments.

The Dillard Lab is conducting research to assess fungicide efficacy for disease control and to evaluate tolerance of several snap bean varieties to P. capsici.

Snap bean pods infected with P. capsici turn white and are shriveled. Note senescing and dead leaves.


Early stage of Phytophthora blight on snap bean pods and stems.  Note premature senescing of infected leaves.