Sensitivity of Uncinula necator to Benomyl, Triadimefon, Myclobutanil, and Fenarimol in California

Abstract

Sensitivity of Uncinula necator subcultures to benomyl and the demethylation-inhibiting (DMI) fungicides triadimefon, myclobutanil, and fenarimol was assessed in 1993, 1994, and 1995 with leaf disk bioassays. In 1993, 1994, and 1995, 81.8, 96, and 96.7% of the subcultures, respectively, did not grow on leaf disks treated with 30 mg of benomyl per liter, whereas growth of the remaining subcultures was inhibited by more than 90%. Median EC50 values of triadimefon, myclobutanil, and fenarimol decreased from 1993 to 1994, and those of triadimefon decreased again from 1994 to 1995. In the same period, median EC50 values of all three DMI fungicides increased in a vineyard never exposed to DMI fungicides. The highest means and ranges of EC50 values found were those of triadimefon. Means and ranges were lower for myclobutanil and lowest for fenarimol, reflecting differences in inherent activities of the fungicides and po-tential for development of resistance. Pairwise correlations between EC50 values of each DMI fungicide were positive and confirmed earlier indications of cross resistance.

Detection and management of myclobutanil-resistant grapevine powdery mildew (Uncinula necator) in Ontario

“…The first reports of DMI failures to control U. necator in vineyards, referred to as "practical resistance" (field resistance), were from California in 1985 and 1986 (Gubler et al 1996;Ogawa et al 1988;Ypema et al 1997), Portugal in 1988 (Steva 1994), and Australia (Savocchia et al 1999). Powdery mildew isolates resistant to triadimefon were crossresistant to myclobutanil and fenarimol, with the latter two compounds being more fungitoxic and having lower resistance factors (Erickson and Wilcox 1997;Gubler et al 1996).…”

Fungicide Resistance in Cucurbit Powdery Mildew Fungi

“…This phenomenon could be interpreted as the persistence of strains with increasing levels of insensitivity, which were incorporated into the CPM populations by mutation, migration, and/or gene flow (McDonald & Linde, 2002). Elimination of these strains in the same manner as occurred for fenarimol (Ypema et al, 1997) could be a possible explanation for increased efficacy of dinocap in 2006 and 2007. This fungicide appears to still be highly effective for control of Czech CPM populations.…”

“…Thiophanate-methyl has been mentioned in reports of resistance only from the USA (Matheron & Porchas, 2007;McGrath, 2001McGrath, , 2005. Occurrence of benzimidazole resistance has been reported in other pathogens, including Didymella bryoniae (Keinath et al, 1998 and Uncinula necator (Ypema et al, 1997).…”

“…Blumeria graminis f.sp. hordei (Buchenauer et al, 1984) and Uncinula necator (Ypema et al, 1997). Cross-resistance of fenarimol-resistant Px strains to some other DMI fungicides was documented in the Netherlands and Israel (Scheppers, 1983;1985), the United Kingdom (Kendall, 1986) …”

Palmolive® detergent controls apple, cherry, and grape powdery mildew

“…Fungicides commonly used to control powdery mildew of apple, cherry, and grape are either demethylationinhibiting (DMI) or quinine outside inhibiting fungicides or a combination of these. Unfortunately, E. necator has developed resistance to DMI fungicides in California (Ypema et al 1997), New York (Erickson and Wilcox 1997) and Ontario (Northover and Homeyer 2001). Resistance was also detected to E. necator in quinine outside inhibiting fungicides in New York (Wong and Wilcox 2002) and is likely to spread to other growing Abbreviations: CFU, colony forming units; DMI, demethylation-inhibiting areas.…”