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

Abstract

Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is a common foliar disease on golf courses. Of 284 isolates collected from Tennessee and northern Mississippi, 90 were tested for in vitro resistance to three commonly used fungicides. The estimated fungicide concentration required to inhibit growth by 50 and 90% varied among locations. Isolates at seven locations were resistant to iprodione, whereas isolates were resistant to propiconazole at only one location. Isolates at five locations were resistant to thiophanate‐methyl. Some isolates showed resistance to 1000 μg a.i. mL−1 iprodione and thiophanate‐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. homoeocarpa 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

Resistance of Kansas Sclerotinia homoeocarpa Isolates to Thiophanate-Methyl and Determination of Associated β-Tubulin Mutation

“…Of those, only two were sensitive to thiophanate-methyl. These results are similar to studies in other states and regions that detected a high frequency of resistance (1,9,10,25). Detailed application histories were not available, but most golf courses had some history of applying thiophanatemethyl ranging from rare (once per year or less) to occasional (2-3 times per year).…”

“…Specifically, resistance to MBC fungicides was first reported in the 1970s in isolates from several areas in the eastern and midwestern United States (30) and since then has been documented in numerous other locations (1,2,5,10,25). Sensitivity of S. homoeocarpa isolates to MBC fungicides has not been examined in Kansas.…”

Resistance to Dicarboximide Fungicides in a Canadian Population of Microdochium nivale

“…Instances of field resistance to iprodione have been reported in other economically important plant pathogen species. Sclerotinia homoeocarpa , another important pathogen of turf, has had EC 50 values of iprodione‐field‐resistant isolates reported at 381 (Detweiler et al, 1983) and 360 μg mL −1 (Bishop et al, 2008). The widely studied species B. cinerea has had EC 50 values for iprodione‐resistant isolates reported several times: 4.3 to 13.9 μg mL −1 (LaMondia and Douglas, 1997), 1.58 to 3.01 μg mL −1 (Raposo et al, 2000), and 16.1 to 96.1 μg mL −1 (Weber, 2011).…”

“…Instances of field resistance to iprodione have been reported in other economically important plant pathogen species. Sclerotinia homoeocarpa, another important pathogen of turf, has had EC 50 values of iprodione-fieldresistant isolates reported at 381 (Detweiler et al, 1983) and 360 mg mL −1 (Bishop et al, 2008). The widely studied calculated a resistance factor of 12 for their resistant isolates and stated that "Fusarium patch symptoms (on the course greens) were common despite, in some instances, the regular and repeated use of iprodione."…”

Effect of Oriental Mustard (Brassica juncea) Seed Meal for Control of Dollar Spot on Creeping Bentgrass (Agrostis stolonifera) Turf

“…Overdependence on synthetic fungicides has resulted in selections of resistant S. homoeocarpa populations. Since the earliest report in the 1960s (Cole et al, 1968; Warren et al, 1974), populations of S. homoeocarpa have developed resistance to almost all of the fungicides used on turf, including benzimidazole and cadmium fungicides (Burpee, 1997; Couch and Smith, 1991; Warren et al, 1974) and dicarboximides and demethylation inhibitor fungicides (Bishop et al, 2008; Detweiler et al, 1983; Detweiler and Vargas, 1982; Golembiewski et al, 1995; Jo et al, 2006). Cross‐ and multiple resistance to more than one chemical family has also been reported (Golembiewski et al, 1995; Vargas et al, 1992).…”