VIEW ARTICLE

Ecology and Epidemiology

Preemergence Herbicides and the Severity of Leaf Spot Caused by Drechslera sorokiniana on Poa pratensis. Clinton F. Hodges, Professor of horticulture and of plant pathology, Department of Horticulture, Iowa State University, Ames 50011; Phytopathology 71:720-722. Accepted for publication 22 December 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-71-720.

Four preemergence herbicides (benefin, bensulide, dacthal [DCPA], and siduron) were evaluated for effect on the severity of leaf spot caused by Drechslera sorokiniana on Poa pratensis. On leaves of plants not previously exposed to the herbicides and inoculated with conidia in aqueous droplets containing the various herbicides, leaf spot development either was not affected or was inhibited by all concentrations tested. Leaf spot development was inhibited, not affected, or stimulated on plants previously exposed to the herbicides by soil application and inoculated with conidia in water droplets. Benefin at all concentrations inhibited leaf spot development. Concentrations of 10^–12, 10^–9, and 10^–6 of DCPA inhibited, had no effect, and stimulated leaf spot, respectively. Siduron stimulated leaf spot at l0^–12 M but had no effect at other concentrations. All concentrations of bensulide stimulated leaf spot. The results suggest that, except for benefin and bensulide, stimulation or inhibition of D. sorokiniana leaf spot by preemergence herbicides is concentration specific.