Disease Note:

Occurrence of Fusarium Wilt of Beans in Colorado. H. F. Schwartz, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. M. S. McMillan, and M. J. Silbernagel. Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523, and USDA-ARS, IAREC, P.O. Box 30, Prosser, WA 99350. Plant Dis. 73:518. Accepted for publication 14 March 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0518D.

In northeastern Colorado in 1987 and 1988, Fusarium wilt of beans (Phaseolus vulgaris L.) caused by Fusarium oxysporum Schlecht. f. sp. phaseoli Kendr. & Snyder was observed in commercial fields of cv. Pinto where plants were stressed by high temperature, poor water drainage, and soil compaction. Typical symptoms of infection included plant stunting, yellowing of lower leaves, gradual to rapid defoliation during late pod fill, and reddish purple to reddish orange discoloration of root and stem vascular tissues up to the third and fourth nodes. Isolates from discolored vascular tissues in the first and second internodes were pathogenic to cultivar U.1. 114, as determined by a seedling inoculation method with root pruning, then incubation at 24-30 C in the greenhouse for 4 wk. In 1988, U.1. 114 was the most severely affected cultivar, with greater than 75% defoliation at 75 days after planting in a replicated yield trial in a commercial field infested with the Fusarium wilt pathogen. Other cultivars were less affected by the pathogen and produced similar yields in infested and noninfested fields. Fusarium wilt of beans has not previously been reported to be economically important in Colorado or other western states.