VIEW ARTICLE

Disease Control and Pest Management

Interaction of Sequential Leaf Senescence of Poa pratensis and Pathogenesis by Drechslera sorokiniana as Influenced by Postemergent Herbicides. Clinton F. Hodges, Professor of Horticulture and of Botany and Plant Pathology, Department of Horticulture, Iowa State University, Ames 50011; Phytopathology 70:628-630. Accepted for publication 10 December 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-628.

The influence of four chlorophenoxy (2,4-D, 2,4,5-T, 2,4,5-TP, MCPP) and one benzoic acid (dicamba) postemergent herbicides on pathogenesis by Drechslera sorokiniana on progressively older leaves of Poa pratensis was determined. Disease increased on each successively older leaf of untreated control plants and a direct relationship was established between increasing leaf senescence and pathogenesis. The soil-drench application of 2,4-D and the spray and soil-drench application of 2,4,5-T, MCPP, and dicamba increased the level of disease on leaves of all ages above that of the controls and on each older leaf of the plants in the respective treatments. Spray-applied 2,4-D had little influence on pathogenesis, and spray-applied 2,4,5-TP decreased disease. Extensive chlorosis and straw-colored blighting was associated with pathogenesis on the two oldest leaves of shoots exposed to 2,4,5-T, MCPP, and dicamba and was suggestive of premature leaf senescence. Little chlorosis and blighting occurred on the two oldest leaves of infected plants not exposed to the herbicides and no chlorosis occurred on uninoculated controls. It was hypothesized that the increase in pathogenesis by D. sorokiniana on progressively older leaves of plants exposed to auxinlike herbicides is the function of a host-pathogen-herbicide interaction that enhances the rate of sequential leaf senescence.