VIEW ARTICLE

Ecology and Epidemiology

Effects of Row Width and Plant Growth Habit on Septoria Brown Spot Development and Soybean Yield. J. K. Pataky, Graduate research assistant, and research plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Department of Plant Pathology, University of Illinois, Urbana 61801, Present address of senior author: Department of Plant Pathology, North Carolina State University, Raleigh 27606; S. M. Lim, associate professor, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 71:1051-1056. Accepted for publication 26 January 1981. 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, 1981. DOI: 10.1094/Phyto-71-1051.

The effects of row width and soybean growth habit on the development of Septoria brown spot and on reductions of yield or seed weight due to brown spot were studied at two Illinois locations. In plots of artificially inoculated and naturally infected soybeans, the vertical progress of brown spot was greater for Elf, a determinate cultivar, than for Williams, an indeterminate cultivar. Brown spot severity and area-under-the-disease-progress-curve (AUDPC) were similar for both cultivars. Differences in disease severity among plots with 17-, 50-, and 75-cm row widths were not consistent although there was a trend toward greater brown spot infection at wider row widths. In inoculated plots, brown spot reduced yields from 12.9 to 20.8% for Elf and from 7.6 to 14.1% for Williams. The disease parameters that correlated best with yield reductions were disease severity at the R5 growth stage, brown spot vertical progress at the R6 growth stage, and AUDPC. Results indicate that planting soybeans in narrow rows will not increase brown spot; however, growing semidwarf determinate cultivars may increase losses due to this disease.