Uncinula necator retains high resistance levels to triadimefon in a survey of California populations despite product absence for fourteen years

• Author(s): Gubler, W.; Miller, Thomas;
• Abstract: Triadimefon was introduced into California vineyards in 1982. In 1985 the first incidences of resistance occurred in the Central Coast production area. In 1986 resistance was recorded in all production regions in CA. In regions where cleistothecia function in the disease cycle, the highest degree of resistance to triadimefon and cross resistance to myclobutanil and fenarimol occurred. Sensitivity within the California population of Uncinula necator to the fungicide triadimefon (Bayleton 50DF Bayer AG, Kansas City, MO) was assayed to question the possibility of sensitivity reversion after 14 years of non-use in grapevine. We determined EC50 values and the distribution of sensitivities within the major grape producing regions of California in order to compare these data with past reports issued from our laboratory using the same methods. The population exhibited a log-normal distribution of sensitivities among isolates arrayed over higher EC50 values than our last reports, indicating resistance has increased.
• Publication Date: Jun 2003
• Journal: Phytopathology