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    Phellinus weirii causes laminated root rot (LRR), a major disease affecting growth and survival of Pseudotsuga menziesii (Douglas-fir) and other commercially important conifer species throughout the Pacific Northwest. Increasing tree vigor and resistance to pathogens through application of K fertilizer is a suggested disease management strategy and one we wished to test. Plots were established with Douglas-fir seedlings planted densely (12,000 seedlings ha-1) around stumps of LRR-killed trees on a harvested site west of the Cascade Range crest near Morton, Washington. Treatments, randomly assigned to plots, were: 224 kg K ha-1, 448 kg K ha-1, 224 kg K + 224 kg N ha-1, and a no-fertilizer control, with 11 replicates. Roots of seedlings receiving the K + N treatment showed the only increase in phenol/sugar (PIS) ratios after one growing season, owing to a reduction in sugar concentrations. Although increases in PIS ratios are negatively correlated with fungal infection rates, the LRR mortality for all fertilizer treatments, including the K + N, was similar to the mortality on the no-fertilizer plots 7 years post-treatment. For this study site we concluded that the single application of K or K + N to Douglas-fir at the rates tested were not an effective management strategy for LRR.

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    Thies, Walter G.; Kelsey, Rick G.; Westlind, Douglas J.; Madsen, Jeff. 2006. Potassium fertilizer applied immediately after planting had no impact on Douglas-fir seedling mortality caused by laminated root rot on a forested site in Washington State. Forest Ecology and Management. 229: 195-201


    defensive chemicals, root disease, plant nutrients, laminated root rot

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