Evaluation of DMI fungicides for management of apple scab in a DMI-resistant ‘Empire’ orchard, 2006

摘要

Trials were conducted in a 11-year-old orchard of trees in Geneva, NY. Each test plot contained one ‘Empire’ (M.9 rootstock) and one ‘Jonagold’ (M.9/M.111 interstem rootstock) tree. Treatments were arranged in a randomized completeblock design with four replications. All treatments were applied dilute to drip using a high-pressure handgun (300gal/acre). Cover sprays were applied with an airblast sprayer at 3X concentration. Ascospore release was monitored from 5 Apr through 20 Maywith a Burkard spore trap. Ascospore counts were assessed in hourly increments during periods of rain andwere combined for the infection events summarized in Table 1. The ascospore dose in the orchard was moderate due to commercially acceptable scab control in 2005. With eight infection periods, disease pressure in 2006 was high. The pathogenpopulation in the test orchard reflected the status of practical resistance to commercially available DMI fungicides. Emphasis was placed on the post-infection performances of the commercial DMI Nova (myclobutanil) in comparison to the experimental DMIsTopguard (flutriafol) and Enable (fenbuconazole). The protective fungicide Dithane alone applied at the low label rate or mixed with Captan served as comparative controls in the post-infection trials. The scab program was initiated with a post-infectionapplication in response to the severe infection period on 22-24 Apr accompanied by the mostmassive discharge of ascospores (Table 1). Scab incidences recorded on 12 Jun reflected the control provided by all five treatments of the trial program (Table 2).