Tomato Diseases


Late Blight
Phytophthora infestans

Found in temperate climates and tropical highlands

Damage Symptoms

All aboveground plant parts may be affected:

Leaves: Irregular water-soaked patches may expand to cover large areas of a leaf. White fungal sporulation may be observed on the underside. Later the lesions dry and turn brown. Blighting of the entire foliage may occur.

Stem: Irregular water-soaked lesions may progress and kill sections of stems and petioles, or they may remain superficial and dry out to form dark brown lesions.

Fruit: Firm, olive to brown, irregular shaped areas that cause the fruit to have a rough, leathery surface. Lesions may enlarge to encompass the entire fruit.


Conditions for Development

Extended periods of leaf wetness from frequent rain or dew formation, and cool to moderate temperatures are required. Hot, dry weather stops disease development.

The fungus persists on tomato and potato plants and in potato tubers. It cannot survive on decayed tissue. Many strains attack both tomato and potato. The spores are spread by wind and splashing rain. Free water on plant surfaces is required for germination and penetration. 

Close-up of leaf lesions

Rough, firm lesions on fruit