What causes potato and tomato late blight?
Late blight is caused by Phytophthora infestans, a fungus-like organism. This pathogen is an obligate parasite, which means that it can only survive on a host: it cannot live in soil or dead plant debris. This organism will not survive long in soil or away from association with a living host. What conditions favor development of late blight? Cool, moist weather is conducive to the development of the disease. Nighttime temperatures in the 50s and daytime temperatures in the 70s accompanied by rain, fog, or heavy dew are ideal late blight conditions. How do I recognize late blight? Late blight lesions can occur on all aboveground plant parts of tomatoes and potatoes. Leaf lesions first appear as fast-growing, irregularly shaped, pale to dark‑green water‑soaked spots. These usually appear at the tips of the leaves or on actively growing tissue. The lesions enlarge rapidly and form brown to purplish‑black areas of dead tissue with indefinite borders. A yellowish‑green halo will usually sur
