Prevalence and Distribution of Aphanomyces euteiches and Phytophthora medicaginis in Iowa Alfalfa Fields. G. P. Munkvold, Assistant Professor; Department of Plant Pathology, Iowa State University, Ames 50011. W. M. Carlton, Research Associate, Department of Plant Pathology, Iowa State University, Ames 50011. PLANT DIS. 79:1251. Accepted for publication 24 August 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1251.

Soil and/or root samples from 122 alfalfa stands in 45 of 99 Iowa counties were collected to determine the presence of Aphanomyces euteiches and Phytophthora medicaginis. Collections were made from sites believed to have a high probability of root disease problems. The presence of these fungi was assayed by baiting soil and root samples with healthy alfalfa seedlings (cv. Vernal) in water or metalaxyl (5 μg/ml) in petri dishes. A. euteiches and P. medicaginis were recovered from 74 and 35% of soil samples and 17 and 8% of root samples, respectively. Of the soil samples infested with P. medicaginis, 81% also were infested with A. euteiches. A. euteiches and P. medicaginis were detected in 31 and 26 counties, respectively. A. euteiches was recovered from 89% of sites in Northeast Iowa (the area with the greatest alfalfa production). A. euteiches may be more prevalent than P. medicaginis in poorly drained or diseased fields in Iowa.

Keyword(s): Medicago sativa, root rot, seedling blight