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Fusarium Root Rot of Douglas-Fir Seedlings. W. J. Bloomberg, Forest Pathologist, Canadian Forestry Service, Department of Environment, Pacific Forest Research Centre, Victoria, British Columbia; Phytopathology 63:337-341. Accepted for publication 3 October 1972. DOI: 10.1094/Phyto-63-337.

Incidence of root rot disease of Douglas-fir seedlings caused by Fusarium oxysporum varied significantly among seedling provenances, sampling years, nurseries, and seedbeds within nurseries. It was greater on the north side of beds with sideboards than on the south side, and in spring-sown open beds than in fall-sown closed beds. It was not correlated with seed germinability, seedling stand density, or seedling size and weight. The disease was most prevalent in seedlings transplanted into infested soil up to 30 days after sowing, and was virtually absent in older transplants; symptoms did not occur until several months after transplanting. Disease incidence was greatly increased by temperatures exceeding 23 C for more than 6 hr/day during the 1st month after sowing. However, temperature had no effect in soil containing high Streptomyces populations. Single seedling infections significantly outnumbered group infections. The disease occurred from May to February, peaking in late August. It was distributed randomly within beds.

Additional keywords: Pseudotsuga menziesii.