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Factors Affecting Efficacy of Metham Applied Through Sprinkler Irrigation for Control of Allium White Rot. P. B. Adams, Plant Pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, USDA, Beltsville, MD 20705. S. A. Johnston, Plant Pathologist, Department of Plant Pathology, Cook College, New Jersey Agricultural Experiment Station, Rutgers Research and Development Center, Bridgeton 08302. Plant Dis. 67:978-980. Accepted for publication 10 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-67-978.

In the laboratory, metham applied to soil columns as a drench killed 50% of the sclerotia of Sclerotium cepivorum at 1617 μg/ml and 95% of the sclerotia at 50 μg/ml. Maximum kill of sclerotia by metham was obtained from 12 to 24 hr after application. Soil pH had little effect on the efficacy of metham, but at low soil temperature (5 C), more time was required to kill sclerotia. In soil columns, only 55% of the sclerotia were killed in the top 2 cm of soil, whereas at greater depths, nearly 100% of the sclerotia were killed. High concentrations of metham applied to soil columns were made ineffective by a subsequent drench of water. Metham applied through sprinkler irrigation at 234 L/ha with 2.5 cm of water provided 94% control of white rot on bunching onions and 30% control on leeks in field tests. The poor level of control on leeks may have been due to rain (31 mm) that fell on the field after metham application.