An assessment of sensitivity to fungicides in Tennessee isolates of the cucurbit powdery mildew pathogen, Podosphaera xanthii
S. C. BOST (1)
(1) University of Tennessee, Nashville, TN, U.S.A.
Phytopathology 100:S16

Seven Tennessee isolates of the cucurbit powdery mildew pathogen, Podosphaera xanthii, were tested for sensitivity to several fungicides in 2009. Comparison of the results to two earlier surveys (1998 and 2004) indicates that the incidence of high levels of resistance to the strobilurins increased from zero in 1998 to 100 percent in 2009. Systemic fungicides had not been used in any of the fields sampled in 2009, and two of the fields were organic production. High levels of resistance to the benzimidazoles were found in all isolates in all three surveys. All isolates tested in the 2009 survey were highly sensitive to myclobutanil, boscalid, sulfur, cyprodinil plus fludioxonil, fenthiopyrid, and quinoxyfen. However, the survey results conflicted with recent anecdotal field reports indicating undesirable levels of control by myclobutanil. The powdery mildew population present in a fungicide efficacy field trial did not change in sensitivity to any of the tested products, based on the results of greenhouse tests conducted on samples collected before the first application and after the final application.