Pierce's Disease
Research Updates

piercesdisease.cdfa.ca.gov

What is Pierce's Disease?

Pierce's Disease is a bacterial infection, which is spread by bugs that feed on grapevines, particularly the "glassy winged sharpshooter." Grapevines that become infected with PD can quickly become sick and die.

glassy-winged sharpshooter

Sensitivity of california isolates of Uncinula necator to trifloxystrobin and spiroxamine, and update on triadimefon sensitivity


  • Author(s): Gubler, W.; Miller, Thomas;
  • Abstract: Sensitivities of Uncinula necator to spiroxamine and trifloxystrobin were established by assay of 36 and 35 isolates, respectively, recovered from California grape vineyards in 2002 and increased as single-spore lines for laboratory testing. Twenty-nine single-spore isolates also were evaluated for levels of sensitivity to the fungicide triadimefon to determine if there had been a reversion to sensitivity following the development of resistance in 1986. Although triadimefon use was limited after 1992, other demethylation inhibitor (DMI) fungicides (fenarimol and myclobutanil) were used extensively in California vineyards. For spiroxamine, the sample mean value of the median effective concentration (EC50 value) was 365 mug/liter (95% confidence interval (CI) from 251 to 531 mug/liter) and values were distributed log-normally. The corresponding mean for trifloxystrobin was 12.8 mug/liter bounded by 8.9 to 18.5 mug/liter for the 95% CI. Statewide, the triadimefon mean EC50 was 8.8 mg/liter, bounded by a 5.3 to 14.5 mg/liter 95% CI, and those values were significantly higher than those obtained in the last assay 12 years earlier. Significant differences in sensitivity of U. necator to triadimefon were detected at a regional scale by comparison of mean EC50 values of frequency distributions representative of regions within California, although the relations between those regions were different from the prior survey.
  • Publication Date: Nov 2004
  • Journal: Plant Disease