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Soil Fertilization, Fumigation, and Temperature Affect Severity of Black Root Rot of Slash Pine. S. J. Rowan, Plant Pathologist, Southeastern Forest Experiment Station, Forest Service, USDA, Forestry Sciences Laboratory, Athens, Georgia 30601; Phytopathology 61:184-187. Accepted for publication 11 September 1970. DOI: 10.1094/Phyto-61-184.

Fumigation with methyl bromide apparently eliminated natural soil populations of Macrophomina phaseolina, significantly reduced soil populations of Fusarium oxysporum, and effectively controlled black root rot of slash pine. The combination of high soil temp, nitrogen (N) fertilization, and the presence of both M. phaseolina and F. oxysporum produced the most severe root rot symptoms. Nitrogen significantly increased seedling growth, but also increased root rot severity and seedling mortality. Potassium (K) significantly increased seedling top growth at 24 C and seedling mortality at 35 C, but did not increase disease severity or root growth at either temp. The mortality of K-fertilized seedlings apparently was caused by the interaction of K and high soil temp. Phosphorus (P) did not affect seedling growth, root rot severity, or seedling mortality. Fumigation and N, P, and K fertilization also affected the percentage of seedlings from which the two fungal pathogens were isolated.

Additional keywords: Charcoal rot, Pinus elliottii var. elliottii.