Leaf Spots of Big Bluestem, Little Bluestem, and Indiangrass Caused by Ascochyta brachypodii. K. E. Zeiders, Research Plant Pathologist, U.S. Regional Pasture Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University Park, PA 16802. Plant Dis. 66:502-505. Accepted for publication 19 September 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, 1982. DOI: 10.1094/PD-66-502.

Ascochyta leaf spot was the most important disease on big bluestem (Andropogon gerardi), little bluestem (A. scoparius), and indiangrass (Sorghastrum nutans) in Pennsylvania and New York from 1976 through 1980. A Didymella sp., which was shown for the first time to be the ascigerous state of A. brachypodii, was also associated with the disease on these species. The morphology and cultural characteristics of A. brachypodii and its Didymella state are described. In greenhouse inoculations, isolates of A. brachypodii from big bluestem, little bluestem, and indiangrass were not equally pathogenic on the three hosts. Three other warm-season grasses—caucasian bluestem (Bothriochloa caucasica), old world bluestem (B. ischaemum), and switchgrass (Panicum virgatum)—and eight cool-season grasses were not susceptible or were highly resistant. Corn (Zea mays) and sudangrass (Sorghum sudanense) were moderately susceptible to A. brachypodii and are reported as new hosts. In field plots, leaf spot was consistently less severe on big bluestem cultivar NY-1145 than on Kaw and Pawnee. Disease severity was related to duration of high relative humidity at two locations. The diseases caused by A. brachypodii on susceptible warm-season grasses can be important in the humid eastern part of their range.

Keyword(s): disease resistance, environmental plant pathology, forage crops.