Use of Leaf Wetness and Temperature to Time Fungicide Applications to Control Botrytis Fruit Rot of Strawberry in Florida.

Botrytis fruit rot (BFR), caused by Botrytis cinerea, is a major disease of strawberry in Florida and is generally controlled by weekly fungicide applications. In this study, disease control programs using fungicides applied on a weekly basis were compared with applications based on three previously published models that correlated disease incidence with weather variables. Field trials were conducted for three seasons on two cultivars, 'Sweet Charlie' and 'Strawberry Festival'. Different thresholds for predicted BFR incidence were evaluated for triggering fungicide applications for the three models. BFR incidence in nontreated control plots of Sweet Charlie and Strawberry Festival was 12.4 and 3.5%, respectively, in 2006-07, 4.2 and 0.8% in 2007-08, and 1.3 and 0.5% in 2008-09. The model of Bulger and associates, with a threshold for disease flower incidence (INF) of 0.50, triggered half or fewer fungicide applications compared with a calendar-standard grower program, without significantly increasing BFR incidence or reducing yield. The model of Broome and associates, at a predicted fruit disease incidence threshold (INF) of 0.62, performed well but required more fungicide applications than the Bulger model (INF ≥ 0.50). The model of Xu and associates, based on field data to predict the incidence of diseased flowers, required more fungicide applications without improving disease control. Use of higher thresholds resulted in fewer applications but increased disease incidence in some cases. The Bulger model utilizing leaf wetness and temperature during the wetness period as input variables and a threshold of INF of 0.50 can be used effectively in a disease-forecasting system to time fungicide treatments, and greatly reduced the number of applications without loss of disease control or yield.