|Leon, Anna -|
|Edmonds, Robert -|
|Littke, Willis -|
|Browning, John -|
|Rose, Robin -|
|Cherry, Marilyn -|
|Davis, E Anne|
|Miller, T -|
Submitted to: Canadian Journal of Forest Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2011
Publication Date: August 29, 2011
Citation: Weiland, G.E., Leon, A.L., Edmonds, R.L., Littke, W.R., Browning, J.E., Rose, R., Cherry, M., Davis, E.A., Beck, B.R., Miller, T. 2011. The effects of methyl bromide alternatives on soil and seedling microbial populations, weeds, and seedling morphology in Oregon and Washington forest tree nurseries. Canadian Journal of Forest Research. 41(8):1885-1896. Interpretive Summary: Six fumigant treatments (four reduced-rate treatments, a conventional methyl bromide treatment, and a nonfumigated control) were evaluated at three forest tree nurseries located in Oregon and Washington for their effects on soil microbes, weeds, and seedling growth in a 2-year study. Eight species of disease-causing microbes were identified before fumigation. All fumigant treatments reduced the amount of disease-causing soil microbes for up to 7 months following treatment and resulted in seedlings with substantially fewer disease-causing microbes on their roots. In contrast, bacteria that inhibit disease-causing microbes increased in fumigated plots. Weeds were only significantly reduced by fumigation only at one nursery. However, seedling size was significantly greater in all fumigated plots. Nonfumigated plots yielded the least number of seedlings and had the greatest number of diseased seedlings. No differences were observed between the efficacy of conventional methyl bromide treatment and the reduced-rate fumigants.
Technical Abstract: Six fumigant treatments were evaluated at two forest tree nurseries in Oregon and one forest tree nursery in Washington for their effects on soil microbial populations, weeds, and seedling morphology during a 2-year study. Fusarium commune, F. oxysporum, Gibberella fujikuroi complex, P. irregulare, P. sylvaticum, P. ultimum, C. destructans, and C. didymum were commonly isolated prior to fumigation. All fumigant treatments reduced soil populations of Fusarium, Pythium, and Cylindrocarpon spp. for up to 7 months postfumigation and resulted in seedlings with significantly less colonization by these fungi than in nonfumigated plots. Fluorescent pseudomonad populations, in contrast, increased following fumigation in all treated plots. Weed populations, biomass, and weeding times were significantly reduced by fumigation only at one nursery. However, seedling height, diameter, shoot volume, and root volume were significantly greater in all fumigated plots. Nonfumigated plots had the lowest yield and greatest number of culls. No differences were observed between the conventional methyl bromide/chloropicrin treatment and any of the reduced rate fumigants.