VIEW ARTICLE

Ecology and Epidemiology

Temperature and Humidity Associated with Sporulation of Helminthosporium maydis Race T. Jack R. Wallin, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, and Professor, Iowa State University, Present address: U. S. Department of Agriculture, Agricultural Research Service, University of Missouri, Columbia, MO 65201; Daniel V. Loonan, Research Technician, Agricultural Research Service, U.S. Department of Agriculture, Ames, IA 50010, Present address: U. S. Department of Agriculture, Agricultural Research Service, University of Missouri, Columbia, MO 65201. Phytopathology 67:1370-1372. Accepted for publication 12 May 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1370.

The relationships of time, temperature, and relative humidity to sporulation of Helminthosporium maydis race T were documented by the results of experiments conducted in the dew chamber, in the greenhouse, and in the field. In the dew chamber, precise meteorological criteria were identified for sporulation on plants with Texas male-sterile cytoplasm (Tcms) and on a hybrid of normal (N) cytoplasm; i.e., longer dew period up to 48 hr at higher temperatures to 28 C resulted in greatest spore production. Initial sporulation occurred on Tcms corn in 5 hr at 22 C and on a hybrid of N-cytoplasm corn after a 12-hr dew period at 25 C. In the field, the relationships of time, temperature, and humidity to initiation and quantity of sporulation were not clear; the results were erratic. None or many spores were produced by the same set of weather variables. The accuracy of forecasts of southern corn leaf blight epidemics in the field on the basis of weather criteria identified in the dew chamber remains in doubt.