Occurrence of Iprodione-Tolerant Fusarium nivale Under Field Conditions. G. A. Chastagner, Western Washington Research and Extension Center, Washington State University, Puyallup 98371. W. E. Vassey, Western Washington Research and Extension Center, Washington State University, Puyallup 98371. Plant Dis. 66:112-114. Accepted for publication 14 April 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-112.

Twenty-one of 24 isolates of Fusarium nivale obtained from two golf course greens where iprodione failed to control development of Fusarium patch were able to grow on potato-dextrose agar amended with iprodione at ≥10 µg a.i./ml. Iprodione had been applied six times on both greens during 1977–1978 and four times during 1978–1979. Only one of eight isolates of F. nivale obtained from diseased turf that had never been sprayed with iprodione was able to grow on potato-dextrose agar amended with iprodione at 10 µg a.i./ml, and its growth was limited. Iprodione-tolerant isolates were cross-tolerant to vinclozolin and procymidone. Growth of tolerant isolates was significantly less than of sensitive isolates on unamended potato-dextrose agar. Tolerant isolates were pathogenic on Penncross bentgrass, and an application of iprodione at the highest labeled rate was ineffective in controlling disease.

Keyword(s): dicarboximide fungicides, resistance.