Resistance of Sclerotinia homoeocarpa to Iprodione, Propiconazole, and Thiophanate- Methyl in Tennessee and Northern Mississippi

Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is a common foliar disease on golf courses. Of 284 isolates collected from Tennes- see and northern Mississippi, 90 were tested for in vitro resistance to three commonly used fungicides. The estimated fungicide concentra- tion required to inhibit growth by 50 and 90% varied among locations. Isolates at seven loca- tions were resistant to iprodione, whereas iso- lates were resistant to propiconazole at only one location. Isolates at fi ve locations were resistant to thiophanate-methyl. Some isolates showed resistance to 1000 μg a.i. mL -1 iprodione and thi- ophanate-methyl, whereas resistance occurred at 10 μg a.i. mL -1 propiconazole. Isolates at only one location exhibited resistance to both thiophanate-methyl and iprodione, and isolates at only one location had resistance to all three fungicides. This study revealed that resistance to fungicides has developed in S. homoeo- carpa in Tennessee and Northern Mississippi. These results also support the contention that repeated use of these three classes of fungicide may lead to development of resistant isolates of S. homoeocarpa.