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Factors Influencing Uptake, Concentration, and Persistence of Benomyl in American Elm Seedlings. W. K. Hock, Plant Pathologist, Crops Research Division, ARS, USDA, Delaware, Ohio 43015; L. R. Schreiber(2), and B. R. Roberts(3). (2)(3)Plant Pathologist and Plant Physiologist, respectively, Crops Research Division, ARS, USDA, Delaware, Ohio 43015. Phytopathology 60:1619-1622. Accepted for publication 8 June 1970. DOI: 10.1094/Phyto-60-1619.

Benomyl fungicide, applied to 4- to 5-month-old container-grown American elm seedlings, was absorbed by the roots and translocated throughout the plants. Zones of inhibition, around tissue sections placed into petri plates containing potato-dextrose agar seeded with Ceratocystis ulmi conidia, were considered indicative of the relative concentration of fungitoxicant in the plants. The concentration of fungitoxicant in seedlings that received three or more applications of benomyl increased only slightly beyond the third application. Seedlings contained a high concentration of fungitoxicant 110 days after the last of three applications of benomyl. The amount of fungitoxicant in seedlings, similarly treated and then transplanted to untreated sand, declined between 10 and 40 days after treatment. Composition of the planting medium influenced uptake of benomyl. The sizes of the diameter zone of inhibition around tissue sections from plants grown in sand were 1.5 to 2.5 times larger than from plants grown in a silt loam soil, and 2 to 6 times larger than from plants grown in a mixture of soil, peat, and perlite.