Phytophthora infestans is the oomycete responsible for both Tomato Late Blight and Potato Late Blight and was the cause of the 1840 Irish Potato famine.
It also attacks other members of the solanacea family including petunia and nightshade affecting all above-ground portions of the plant. Symptoms appear first on the younger leaves as irregularly shaped lesions and white cottony growth on the underside of the leaf.
Cool (nights in the 50s-60s and days in the 80s), wet weather and clouds provide optimal conditions for the disease.
Tomato Late Blight image by Gerald Holmes – Bugwood
Management
- Grow resistant varieties
- Plant early in the season
- Prevent water from staying on leaves
- Remove infected leaves, fruit, plants, and weeds
