Effect of Plant Nutrition on Susceptibility of Chrysanthemum morifolium to Erwinia chrysanthemi. R. J. McGovern, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. R. K. Horst, and R. S. Dickey, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. 69:1086-1088. Accepted for publication 19 June 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1086.

Susceptibility of Chrysanthemum morifolium cv. Bonnie Jean to Erwinia chrysanthemi was affected by rate of complete fertilizer (NPK, 20-10-20) and by form of nitrogen. The rate of complete fertilizer was varied from 0 to a concentration containing about 473, 105, and 413 ppm of nitrogen, phosphorus, and potassium, respectively. In separate experiments, three forms of nitrogen were varied from 0 to 400 ppm. Susceptibility was based on the amount of pith maceration in cuttings 4 days after dip inoculation in a bacterial suspension containing about 10⁸ colony-forming units per milliliter. Susceptibility increased with increasing rates of complete fertilizer and nitrogen in the form of (NH₄)₂SO₄. However, susceptibility was maximal at moderate levels of Ca(NO₃)₂ and NH₄NO₃ (100–200 ppm of nitrogen) and decreased when nitrogen was increased to 400 ppm in both forms.