How to Manage Pests

Pests in Gardens and Landscapes

Late blight—Phytophthora infestans

Phytophthora infestans has a wide host range, including tomato, potato, pepper, and eggplant. On leaves, late blight lesions typically first appear as irregular, small pale to dark green water-soaked spots that are surrounded by a zone of yellowish tissue. Lesions may expand rapidly and become brown to purplish black. White sporulation of the fungus may be observed at the periphery of lesions, principally on the underside of leaves. On stems and petioles, lesions are brown to black and may also support sporulation of the fungus. Fruit discoloration usually begins on the upper side of the fruit. Affected fruit remain firm. Tubers develop a firm brown decay.

Life cycle

Solutions

Use certified plants and tubers. When late blight has developed on foliage and fruit or tubers are at a risk of infection, make sure that vines have been completely dead for 2 – 3 weeks before harvest as the fungus does not survive very long in dead foliage. Avoid sprinkler irrigation. Destroy all tomato, potato, eggplant, and pepper debris after harvest.

Late blight infection on tomato leaves

Late blight infection on tomato leaves

Tomato fruit discoloration

Tomato fruit discoloration

Late blight symptoms on potato leaves

Late blight symptoms on potato leaves

Brown decay in potato tubers

Brown decay in potato tubers


Statewide IPM Program, Agriculture and Natural Resources, University of California
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