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Title: Pythium and Fusarium Species Associated with Production of Douglas-Fir Seedlings

Author
item Weiland, Jerry
item LITTKE, WILL - Weyerhauser Company
item BROWNING, JOHN - Weyerhauser Company
item ROSE, ROBIN - Oregon State University
item EDMONDS, BOB - University Of Washington
item LEON, ANNA - University Of Washington

Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: 9/18/2009
Publication Date: 10/29/2009
Citation: Weiland, G.E., Littke, W., Browning, J., Rose, R., Edmonds, B., Leon, A. 2009. Pythium and Fusarium species associated with production of douglas-fir seedlings. Proceedings of International Research Conference on Methyl Bromide Alternatives. Available: http://www.mbao.org/2009/Proceedings/027WeilandJMBAONov09.pdf

Interpretive Summary: Methyl bromide has long been used to control Pythium and Fusarium spp. in conifer nurseries in the Pacific Northwest. However, alternative fumigants are now necessary as methyl bromide is an ozone-depleting agent. The efficacy of three alternative fumigants (methyl iodide, metam sodium, and dimethyl disulfide) were compared to methyl bromide at three nurseries in western Washington and Oregon. Pathogen populations were assessed by collecting soil samples from each treatment plot before and after fumigation. In addition, mesh packets containing a known quantity of both pathogens were buried in each plot at 6 and 12 inches before fumigation. Each packet was sampled after fumigation to determine the depth at which fumigation was effective. Soil samples and the contents of each mesh packet were then placed on media that were selective for each of the pathogen species, and the number of Pythium and Fusarium isolates were counted. Pathogen isolates were identified on the basis of DNA sequence. All treatments were usually as effective as methyl bromide in reducing pathogen populations.

Technical Abstract: Methyl bromide has long been used to control Pythium and Fusarium spp. in conifer nurseries in the Pacific Northwest. However, alternative fumigants are now necessary as methyl bromide is an ozone-depleting agent. The efficacy of metam sodium, dimethyl disulfide, and methyl iodide against Pythium and Fusarium spp. were tested at three conifer nurseries in western Washington and Oregon under a low permeability fumigation tarp: Virtually Impermeable Film (VIF). Populations of Pythium and Fusarium were assayed from soil samples collected from each treatment plot just prior to fumigation and at 1 and 7 months after fumigation. In addition, inoculum packets containing representatives of each pathogen were buried at 6 and 12 inches in plots before fumigation and removed after fumigation. Pathogen populations were assessed by plating subsamples from soil and inoculum packets on Komada’s medium and PARP, which are semiselective media for Fusarium and Pythium species, respectively. Fusarium isolates were sequenced using translation elongation factor 1-alpha (EF-1a) and Pythium isolates with the internal transcribed spacer (ITS) region. All treatments were usually as effective as methyl bromide in reducing pathogen load.