Effect of Temperature and Wetness Duration on Apple Fruit Infection and Eradicant Activity of Fungicides Against Botryosphaeria dothidea. K. C. Parker, Former Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. T. B. Sutton, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 77:181-185. Accepted for publication 3 November 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0181.

A model to forecast infection of apple (Malus domestica) fruit by Botryosphaeria dothidea was developed based on results of studies with a combination of six temperatures (from 8 to 28 C) and nine wetness durations (from 2 to 48 hr). Fruit infection increased with wetness duration and temperature and could be described by the model y = –0.1546 + 0.0123T + 0.0329W – 0.00169W² + 0.0000225W³ – 0.00153(TW) + 0.000111(TW²) – 0.00000151(TW³), where y = percentage of diseased apple pieces, T = temperature (C), and W = wetness duration (hr). Reduction of growth of B. dothidea on fungicide-amended agar was used to determine EC₅₀ values of nine fungicides: benomyl, bitertanol, fenbuconazole, flusilazole, mancozeb, myclobutanil, penconazole, tebuconazole, and triflumizole. Three of the most active fungicides (benomyl, flusilazole, and tebuconazole), triflumizole, and mancozeb were tested for protectant activity in the field and for after-infection activity in the laboratory and field. No significant difference was detected among the five fungicides in after-infection or protectant activity.