Soil in Field 2 at the USDA Forest Service Nursery, Coeur d'Alene, Idaho was assayed six times over a 2- year fallow period for potentially pathogenic Fusarium and Pythium spp. following incorporation of a corn cover/green manure crop. Populations of potentially disease-antagonistic Trichoderma spp. were also assayed. Soil populations of Fusarium did not decrease over the fallow period and were at sufficient levels after two years to be of concern from a disease potential standpoint. Populations of Pythium were fairly low throughout the monitoring period. Trichoderma populations remained high, but were probably not sufficient to ameliorate Fusarium disease potential. Fusarium spp. readily colonized soil organic matter particularly roots of the previous conifer seedling crop; these fungi also frequently colonized corn organic debris. Fusarium oxysporum was the major potential pathogen colonizing soil and organic matter. When a corn cover/green manure crop is produced within fields destined for conifer seedling production, these fields will require soil fumigation prior to sowing seedling crops to reduce risk of Fusarium-associated diseases.
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