Timing of Fungicide Applications for Botrytis cinerea Based on Development Stage of Strawberry Flowers and Fruit

During the 1999-2000 and 2000-2001 growing seasons, field experiments were conducted to identify the developmental stage(s) of strawberry flowers and fruit that requires fungicide applications to control Botrytis fruit rot. Fenhexamid, a protectant fungicide, was applied to individual newly opened flowers or fruit of cultivar Sweet Charlie at defined intervals after anthesis. In 1999-2000, a single application of fenhexamid at anthesis controlled Botrytis fruit rot as well as multiple weekly applications beginning at anthesis. During both seasons, disease control deteriorated as applications were delayed 7 and 14 days after anthesis. This trend was described by linear regression equations relating the time of application to Botrytis fruit rot incidence. Additional treatments tested the effects of emasculation and petal removal 3 to 7 days after anthesis. Emasculation significantly reduced disease incidence in 2000-2001. Petal removal produced modest but significant reductions in 1999-2000, but not in 2000-2001. These results demonstrate that strawberry flowers are more susceptible to Botrytis cinerea than green fruit, and suggest that stamens are the principal infection court. Fungicide applications should focus on peak bloom periods to minimize fungicide use and optimize control of preharvest Botrytis fruit rot. During these periods, applications should be made at close intervals (≤7 days) to minimize losses to Botrytis.