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Epidemiology and Management of Petunia and Tomato Late Blight in the Greenhouse

Factors affecting the management of petunia and tomato late blight, caused by Phytophthora infestans, under greenhouse conditions were investigated. Late blight-infected petunias (Petunia × hybrida) and tomatoes (Lycopersicon esculentum) each produced sporangia that were dispersed throughout the greenhouse via air currents. Infected petunias produced and released fewer sporangia than infected tomatoes, but infected petunias released sporangia two times longer. Surface-directed irrigation reduced disease incidence compared with overhead irrigation that wetted the foliage. The fungicides dimethomorph-mancozeb, fosetyl-Al, azoxystrobin, and dipo-tassium phosphonate/phosphate suppressed late blight development, as did the plant defense activator acibenzolar-S-methyl. All products were applied twice at 7-day intervals. The other plant defense activator (harpin protein) and the bioantagonists (Trichoderma harzianum, Glio-cladium virens, and Bacillus subtilis) were ineffective at the rates tested.