| Abstract Detail
Plant Protection Fitzpatrick, Erica R. [1], Lambert, David H. [2]. Phytophthora erythroseptica fungicide options and mefenoxam (metalaxyl) insensitivity among isolates in Maine. PHYTOPHTHORA erythroseptica (Pe), causal agent of pink rot, is a major late season and storage disease problem in potato production worldwide. The disease is increasing in incidence, causing large economic losses annually. Pe is controlled by a limited number of fungicides, most containing metalaxyl or its active enantiomer, mefenoxam. However, resistance to mefenoxam was documented in Maine in 1993, and has since been reported in most US potato producing states with widespread resistance in both Maine and Eastern Idaho.
A trial established in 2003 was inoculated with 20% mefenoxam resistant strains to track any yearly increase in resistant isolates. In the absence of mefenoxam applications from 2003-05 the number of resistant isolates recovered using an in-vitro agar assay increased significantly. The increasing proportions of resistant isolates in untreated field trials over a three-year period indicates fitness equal to or greater than that of sensitive isolates. In 2005 over fifty grower storages were sampled for Pe, and mefenoxam sensitivity was determined using an in-vitro assay. Overall, 70% of the 162 isolates recovered were mefenoxam resistant. For the 44% of growers with a recent history of mefenoxam use, 86% of Pe isolates were resistant. Samples collected from growers without a recent history of mefenoxam averaged 49% resistant. The efficacy of mefenoxam in the future is in jeopardy due to the increasing number of mefenoxam resistant Pe populations. Several trials have indicated that there are no alternative fungicides with efficacy comparable to mefenoxam. Phosphorous acid applied in-furrow was not effective in reducing Pe relative to the untreated control. Another product with the active ingredient cyazofamid provided substantial Pe control, reducing Pe rot by more than half. Alternative fungicide options with systemic properties or chemistries that will protect the roots and tubers during the growing season are needed.
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1 - McCain Foods USA, Inc. & University of Maine, Orono, Department of Plant, Soil & Environmental Sciences, 319 Richardson Road, Easton, ME, 04740, US
2 - University of Maine, Department of Plant, Soil & Environmental Sciences, 9 Deering Hall, Orono, ME, 04669, US
Keywords:
Phytophthora erythroseptica
pink rot
fungicide resistance
mefenoxam
metalaxyl
grower survey.
Session: Poster-12
Location: Ballroom CD/Monona Terrace
Date: Tuesday, July 25th, 2006
Time: 8:00 AM
Abstract ID:90 |
