Submitted to: Plant Disease Management Reports
Publication Type: Other
Publication Acceptance Date: April 1, 2008
Publication Date: August 5, 2008
Citation: Porter, L., Coffman, V.A. 2008. Efficacy of seed treatments in reducing seed and root rot of peas in the presence of metalaxyl-resistant Pythium, 2007. Plant Disease Management Reports (online). Report 2:V154. DOI:10.1094/PDMR02. The American Phytopathological Society, St. Paul, MN. Interpretive Summary: Metalaxyl has been used for years as a seed treatment for large and small vegetable seeds in commercial fields to prevent seed and seedling rot due to Pythium fungi. Metalaxyl-resistant isolates of Pythium ultimum have been discovered in irrigated crop fields in Idaho, Washington, and Oregon, posing a potential threat to the effectiveness of this fungicide as a seed treatment. In Washington, the soil from several commercial fields having peas in the crop rotation were identified as having metalaxyl-resistant Pythium. Farm managers have had concerns of whether commercial seed treatments containing metalaxyl are still effective in managing seed rot caused by Pythium species in fields where metalaxyl-resistant Pythium have developed. Therefore, seed treatments specifically selected for their potential to manage seed and root rot caused by oomycete pathogens such as Pythium were tested under commercial field conditions where metalaxyl-resistant Pythium were present. Captan + Allegiance (containing metalaxyl) at the highest commercially recommended seed application rate was the most effective treatment in increasing plant emergence, plant height and yield of all the treatments tested, indicating that even in fields were metaxyl-resistant Pythium fungi have developed, metalaxyl was still the best seed treatment in managing seed and seedling damping off of all the treatments tested. The product, Sil-Matrix was also effective in increasing the pea yields above that of non-treated pea seed. Based on this research, commercial seed treatments containing metalaxyl are still recommended to manage seed and root rot, even in fields were metalaxyl-resistant Pythium have developed.
Technical Abstract: Five organic seed treatments and eighteen commercial seed treatments were evaluated in a commercial pea field (sandy loam soil) in Paterson, WA to manage seed and root rot of processed peas. The soil from the field site had a mean of 89 total Pythium colonies and 27 metalaxyl-resistant Pythium colonies per gram of soil. Plant emergence of seed treated with 17 of 18 commercial seed treatments significantly increased (P < 0.05) emergence above that of the non-treated control (NTC) with Captan + Allegiance at the high commercial rate having the highest emergence rate among the treatments. Plant height of 17 of 18 commercial seed treatments was significantly greater than the NTC with Captan + Allegiance at the high rate having the greatest mean height of all the treatments. Root disease severity was significantly greater than the NTC for 13 of 18 commercial seed treatments, and there were no seed treatments with mean root disease severity values significantly less than the NTC. The foliar dry weight of 4 of 5 of the organic seed treatments was significantly greater than the NTC with Humax + zinc sulfate having the greatest weight, and 6 of 18 commercial seed treatments were significantly less than the NTC. The dry root weight of seed treated with Sil-Matrix, Aliete, molasses, and the Biolink Surfactant were significantly greater than the NTC. Yields of seed treated with Captan + Allegiance at the high rate and Captan + Sil-Matrix were the only treatments that were significantly greater than the NTC. The tenderometer readings for Tachigaren, Captan + Tachigaren, and Magnum were significantly greater than the NTC and tenderometer readings for Sil-Matrix, Captan + Allegiance at the low rate, Ranman, Biolink Surfactant, Humax, and Humax + zinc sulfate were significantly less than the NTC. Captan + Allegiance (metalaxyl) at the high rate appears to be the most effective seed treatment of those tested for use in commercial pea production based on seed emergence, plant height and yield and it was determined that metalaxyl was still effective as a seed treatment, even in the presence of metalaxyl-resistant Pythium. None of the organic seed treatments tested significantly improved yield above that of the NTC and would not be recommended for organic or conventional pea production.