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Increased Plant Mortality Caused by Pythium Root Rot of Poinsettia Associated with High Fertilization Rates. G. W. Moorman, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 70:160-162. Accepted for publication 19 August 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-160.

Rooted poinsettia cuttings potted in peat:perlite, soil:sand:peat, peat:vermiculite, peat:vermiculite:perlite:sand, or peat:vermiculite:sand:bark ash received soluble fertilizer with each irrigation. A range of fertilizer levels from suboptimum (100 Μg N/g) to excessive (600 Μg N/g) was applied. Half of the plants in each treatment were inoculated with Pythium ultimum. Few uninoculated plants died, and few plants given the lowest level of fertilization died even when inoculated with Pythium. Mortality of inoculated plants increased rapidly as the concentration of soluble salts, associated with fertility level, increased. Plants that survived inoculation were significantly shorter than uninoculated plants at all except the highest fertilizer level.