Alternatives to Chemical Fumigation in Bareroot Forest Nurseries: Effects on Pathogen Levels and Seedling Density, Mortality and Quality

Our objectives were to develop cultural approaches aimed at reducing populations of soil-borne pathogenic fungi in forest nurseries to reduce or replace conventional chemical soil fumigation. One threeyear cycle of this study has been completed in seven nurseries in Oregon, California, and Idaho. A second cycle of experiments has been initiated in six nurseries. In the first cycle, non-chemical, cultural methods, including bare fallow, organic soil amendments, seed cover, and time of sowing were compared with methyl bromide (MC-33) or dazomet soil fumigation in reducing preplant pathogen populations. Bare fallow, with or without periodic tilling, was equivalent to chemical fumigation treatments in reducing preplant levels of Fusarium oxysporum. Seedling density and mortality varied among several treatments. but at all nurseries combinations of soil amendments and bare fallowing yielded seedling densities and mortalities equivalent or superior to chemically treated plots. Two-year old seedlings were on average larger and had better developed root systems from fumigated plots in some nurseries. In several nurseries, seedlings from nonfumigated bare fallow plots were equivalent in height and root collar diameter to fumigated treatments. Bare fallowing and other management alternatives may help nurseries control seedling disease problems without or with reduced use of soil fumigants.

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Author(s): USDA Forest Service