Effects of Bare Fallowing on Fusarium-Asoociated Root Diseases and Production of Bare Root Ponderosa Pine Seedlings at the USDA Forest Service Lucky Peak Nursery, Boise, Idaho

A large-scale evaluation was conducted at the USDA Forest Service Lucky Peak Nursery near Boise, Idaho to compare bare fallowing with standard pre-plant soil fumigation with methyl bromide/chloropicrin. Comparisons were made of pre-sowing populations of potentially pathogenic Fusarium spp. and potentially antagonistic Trichoderma spp. In addition, ponderosa pine seedling emergence, density, height, diameter, and biomass production during a typical 2- year growing cycle were also compared. Soil fumigation effectively reduced soil fungal populations while fallowing a field for one growing season resulted in pathogen populations that were high enough to incite disease. Seedling emergence and 1-0 and 2-0 stand densities were significantly lower in the fallowed field; much higher disease levels were also detected in the non-fumigated field. Higher levels of healthy seedling root colonization were found in the fallowed field and pine seedlings were significantly larger in one of the fumigated fields. The major pathogen encountered in all fields was Fusarium oxysporum. In this evaluation, bare fallowing with periodic cultivation for 1 year prior to sowing was not an acceptable alternative to pre-plant soil fumigation with methyl bromide/chloropicrin.

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Author(s): USDA Forest Service