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Activity of Cyprodinil: Optimal Treatment Timing and Site of Action. G. Knauf-Beiter, Ciba-Geigy Ltd., CIBA Crop Protection, Business Unit Disease Control, CH-4002 Basel, Switzerland. H. Dahmen, U. Heye, and T. Staub, Ciba-Geigy Ltd., CIBA Crop Protection, Business Unit Disease Control, CH-4002 Basel, Switzerland. PLANT DIS. 79:1098. Accepted for publication 17 July 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1098.

Cyprodinil, a fungicide with a new mode of action, was recently introduced by Ciba-Geigy for foliar application on cereals, grapes, vegetable crops, and deciduous fruits. In greenhouse studies, the protective and curative activity of cyprodinil was determined against Erysiphe graminis f. sp. tritici on wheat, Drechslera teres on barley, and Venturia inaequalis on apples. Cyprodinil significantly reduced fungal infection stages that are formed after penetration of the leaf. Foliar applications of 600 mg a.i/liter of cyprodinil provided 90 to 100% control of E. graminis leaf symptoms after 7-day protective and 5-day curative applications. Curative applications did not completely prevent symptom development; however, sporulation was reduced 100%. Histological studies showed that secondary haustoria were the stage in the infection cycle of E. graminis most sensitive to cyprodinil. Symptom development of V. inaequalis was reduced 90 to 100% following 6-day protective and 3-day curative applications with 100 mg a.i/liter. This was mainly based on reduction in the growth of the subcuticular stroma. Application of 200 mg a.i/liter of cyprodinil provided 80 lo 90% reduction in lesion area of D. teres within an effective application period lasting from 7-day protective lo 2-day curative. Histological observations of late infection stages of D. teres were difficult, but it is hypothesized that the activity of cyprodinil against D. teres is based on the inhibition of intra- and intercellular mycelial growth.

Keyword(s): anilinopyrimidines, CGA 219417, methionine biosynthesis