University of Florida

Late Blight

Fungus

Phytophthora infestans

Infects

Foliar plant parts and fruit.

Symptoms

Initially on leaves or stems as water-soaked, greasy patches that dry and brown rapidly as if frosted; stem lesions often girdle plant; white fungus obvious from lower leaf surface in cool, moist weather; fruit lesions commonly at stem end onto shoulder of fruit; lesion is brown to mahogany, irregularly shaped, rough textured, with a slightly sunken but indefinite lesion margin; some fruit may exhibit a narrow zonation.

Pathogen Spread

From transplants to field, surviving on volunteer tomatoes or other plants related to tomato.

Favorable Conditions

Seasons with cool nights (50-60 F.) and mild days (60-70 F.). A cold, wet winter problem throughout the state.

Late Blight Pictures

late blight
Image #124.
Late blight-

severe damage to plants in a commercial field.

late blight on leaf
Image # 125.
Late blight-

fuzzy grayish-white fungal growth of the causal fungus reproducing on the leaf underside in moist weather.

late blight - mahogany colored fruit
Image # 125.
Late blight-

mottled mahogany fruit spots with very indefinite borders.