Effectiveness of Fludioxonil, a New-Generation Reduced-Risk Fungicide, Against Brown Rot Pathogens.

Brown rot, caused by Monilinia species, is a destructive disease of pome and stone fruits that can lead to significant losses in production. Disease management is mainly based on fungicide applications during the growing season. Fludioxonil, a "new-generation reduced-risk fungicide", is one of the most important fungicide used. The objectives of the present study were to compare and determine the toxicity of fludioxonil to selected M. laxa, M. fructigena and M. fructicola isolates, to test its effectiveness in detached fruits and to assess its effectiveness under practical control conditions. A total of 27 isolates (10 isolates of M. laxa, 8 of M. fructigena and 9 of M. fructicola) were tested for sensitivity to fludioxonil in vitro. Isolates from each species exhibited a homogeneous response to the fungicide, while differences among the different species were determined. Based on calculated resistance factors (RF), the examined isolates were classified into two categories: sensitive and moderately resistant. In vivo testing of the effectiveness of the label concentration of fludioxonil on detached fruit did not reveal differences between isolates classified into different sensitivity categories; fludioxonil used at the label concentration (0.1%) inhibited decay development 93.5 to 100%, regardless of the isolate category. Field trials revealed the very high efficacy of fludioxonil in preventing brown rot on fruits, ranging from 92.2 to 100 for peach, 90.7 to 97.3 for plum and 84.9 to 91.9% for sour cherry. In conclusion, fludioxonil was highly effective according to in vitro sensitivity tests and when used under practical field conditions for brown rot control.