Effect of fungicide treatments on incidence of powdery mildew of pecan and on pecan nut quality

Abstract

Powdery mildew of pecan, caused by Microsphaera ulni, was observed on pecan shucks by the latter part of June 2000 in a commercial pecan orchard near Sahuarita, Arizona. Results of 1999 studies indicated that infection does not reduce nut quality. In order to determine effects of fungicide treatments and to substantiate results from 1999, preventive applications of micronized sulfur and azoxystrobin were initiated on June 8, 2000 in selected clusters in both Wichita and Western varieties. Trials were established in plots that had a high incidence of powdery mildew in 1999. Whole nut weights, kernel weights, or color ratings were not significantly different among clusters of nuts that were treated with fungicides and untreated nuts that were infected with powdery mildew. Percent disease incidence was 100% in untreated clusters, 0% in clusters treated with azoxystrobin every two weeks, and 5.3% (Wichita) and 8.8% (Western) in clusters treated with sulfur three times early in the season. Results indicate that disease did not affect nut weight or quality and that early preventive fungicide treatments are effective in controlling infections.