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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #321136
Title: Efficacy of reduced rate fumigant alternatives and methyl bromide against soilborne pathogens and weeds in western forest nurseries

Author
item Weiland, Gerald - Jerry
item LITTKE, WILLIS - Weyerhaeuser Company
item BROWNING, JOHN - Weyerhaeuser Company
item EDMONDS, ROBERT - University Of Washington
item Davis, Elizabeth
item Beck, Bryan
item MILLER, TIMOTHY - Washington State University

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2016
Publication Date: 7/1/2016
Citation: Weiland, G.E., Littke, W.R., Browning, J.E., Edmonds, R.L., Davis, E.A., Beck, B.R., Miller, T.W. 2016. Efficacy of reduced rate fumigant alternatives and methyl bromide against soilborne pathogens and weeds in western forest nurseries. Crop Protection. 85:57-64. https://doi.org/10.1016/j.cropro.2016.03.016.
DOI: https://doi.org/10.1016/j.cropro.2016.03.016

Interpretive Summary: Soil fumigation with methyl bromide is used in forest nurseries to control the soilborne diseases and weeds that reduce the number and quality of tree seedlings that are produced for reforestation. However, methyl bromide depletes ozone and is expected to be pulled from use in forest nurseries in the near future. In order to reduce chemical use and protect the environment, a field study was conducted to determine if there were other fumigants that could be used and whether reducing the amount of fumigant applied would still be effective in controlling soilborne diseases and weeds. Biocontrol treatments were also evaluated as alternatives to fumigation. Reduced rates of three fumigants (methyl bromide, metam sodium, and dichloropropene) were applied at two nurseries. Results indicated that all three fumigants were almost equally effective in controlling soilborne diseases and weeds. However, while dichloropropene was slightly more effective in controlling some soilborne diseases, it also slightly reduced the number and quality of seedlings produced in fumigated plots. Therefore, applications rates for dichloropropene may need some adjustment to optimize performance. Biocontrol treatments ultimately were not effective in controlling disease. The results of this study are important because they show that: 1) using less fumigant can still be effective in reducing soilborne diseases and weeds; and, 2) there are two promising alternative fumigants (metam sodium and dichloropropene) that could potentially be used as replacements for methyl bromide. Additional studies are needed to show whether metam sodium and dichloropropene continue to be effective when used over multiple years as some research has shown that the effectiveness of metam sodium may decrease with repeated use.

Technical Abstract: Preplant soil fumigation is commonly used to control soilborne pathogens and weeds in forest seedling nurseries of Oregon and Washington. However, lower chemical inputs are desired to meet state and federal application regulations, and to help protect the environment. Therefore, the objective of this research was to evaluate the efficacy of three reduced-rate soil fumigants under totally impermeable film (TIF) in managing soilborne diseases and weeds and to determine if combined applications of up to four biocontrol agents improved soilborne disease control. Reduced-rates of methyl bromide, metam sodium, and dichloropropene, all applied in combination with chloropicrin, were effective in decreasing soil populations of Pythium and Fusarium as well the presence of Pythium in root debris from the previous crop. Root colonization of Douglas-fir seedlings by these two pathogens was also reduced regardless of the fumigant used. However, biocontrol treatments were not effective against either pathogen. Similar to what was found for soilborne pathogens, weed biomass and weeding times were significantly reduced by fumigation. Application costs were similar across all three fumigant treatments, but seedling quality was best from the methyl bromide and metam sodium treatments followed by the dichloropropene treatment. Based on the results of this study, reduced rates of methyl bromide, metam sodium, and dichloropropene show promise in managing soilborne diseases and weeds in forest nurseries. However, additional studies are needed to evaluate whether metam sodium and dichloropropene continue to be effective when used long-term as some research has shown that the efficacy of metam sodium may decrease with repeated use.