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

      Olsen, M.; Rasmussen, S.; Nischwitz, C.; Wright, Glenn; Kilby, Mike (College of Agriculture, University of Arizona (Tucson, AZ), 2002-02)
      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.
    • Effect of Powdery Mildew on Pecan Nut Weight and Quality

      Olsen, M.; Rasmussen, S.; Nischwitz, C.; Kilby, M.; Wright, Glenn; Kilby, Mike (College of Agriculture, University of Arizona (Tucson, AZ), 2000-10)
      Powdery mildew of pecan, caused by Microsphaera ulni, results in discoloration of pecan shucks, but its effects on yield and quality of kernels are not known. In 1999, powdery mildew was observed on pecan shucks by the latter part of June in a commercial pecan orchard near Sahuarita, Arizona. The fungus continued to be active throughout the summer. However, results of a field test comparing diseased and healthy nuts from two varieties of pecans indicate that powdery mildew did not affect nut weight or quality. Whole nut weights, kernel weights, color ratings or percentage of discarded nuts were not significant between paired clusters of nuts that were treated with fungicides and remained disease free and untreated nuts that were infected with powdery mildew. Although shucks may have a high percentage of area covered by powdery mildew, results from this trial indicate that fungicide treatments are not warranted.