Cucurbit Phytophthora blight/crown rot is a water mold or oomycete disease of cucurbits caused by Phytophthora capsici. It causes large, irregular brown spots on leaves, which expand and coalesce in warm and wet conditions. On vines, water-soaked, dark lesions can girdle the stem and cause whole-plant wilt and collapse. P. capsici also causes damping-off in cucurbits, rotting the crown and root tissues and most often resulting in plant death. Fruit rot often occurs on the side of the fruit touching the soil, beginning as a water-soaked lesion that expands and is covered with white mold. P. capsici is a soil-borne pathogen that survives in the soil and on infected plant debris, spreading in rain, irrigation, and on workers / equipment. Favorable conditions include warm temperatures, high soil moisture, and high humidity.
Cultural management involves planting in fields without a history of Phytophthora blight, and maintaining greater than 3 years between susceptible crops (primarily cucurbit and Solanaceous crops with the exception of potato). Avoid planting in low, poorly-draining areas. Do not land spread culled infected fruit onto production fields. Scout regularly for symptoms – if localized disease areas are located, plow under infected plants. Effective fungicide application should occur during early disease development. Mulching with straw or cover cropping between rows can reduce splash.
