Control of Pythium Blight of Snap Beans by Seed Treatment with Systemic Fungicides. J. C. Locke, Florist and Nursery Crops Laboratory, Horticultural Science Institute, U.S. Department of Agriculture, Beltsville, MD 20705. G. C. Papavizas, J. A. Lewis, and R. D. Lumsden, Soilborne Diseases Laboratory, Plant Protection Institute, U.S. Department of Agriculture, Beltsville, MD 20705; and J. B. Kantzes, Department of Botany, University of Maryland, College Park 20742. Plant Dis. 67:974-977. Accepted for publication 8 March 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/PD-67-974.

The systemic fungicide metalaxyl applied to snap bean (Phaseolus vulgaris) seed directly or with acetone infusion significantly reduced blight in the greenhouse and field in soils naturally infested with Pythium ultimum, P. aphanidermatum, and P. myriotylum. Directly applying as little as 0.2 g a.i./kg of seed using either a 50WP or 2E formulation controlled preemergence damping-off and postemergence blight without phytotoxicity. Efficacy of metalaxyl against blight was reduced during incubation at a high temperature (35 C). Metalaxyl and propamocarb hydrochloride seed treatments generally gave better protection than ethazol against Pythium blight. In liquid culture, metalaxyl had an ED₅₀ of <1 μg a.i./ ml in inhibiting mycelial growth of the three Pythium species, with P. ultimum the most sensitive. Zoospore and oospore germination and sporangial formation were less sensitive to metalaxyl than mycelial growth. Metalaxyl did not affect membrane permeability at 50 μg/ml, and cholesterol had no effect on leakage.

Keyword(s): organic solvent infusion technique.