New Fungicides for Control of Resistant Dollar Spot Populations 2003 Data Dr. Randy Kane, Lee Miller - CDGA October 26, 2003 Fungicide resistant (or "tolerant") dollar spot populations still present a significant challenge to turf managers who must find avenues for control. In some cases, managers are dealing with dollar spot that is resistant to more than one class of fungicide, which compounds the problem by limiting control options. As in previous years, (click here to see 2001-2002 info.) we continue to test systemic fungicides for control of these dollar spot populations. In 2003, we tested a variety of fungicides and fungicide combinations at three sites that have three different circumstances of dollar spot fungicide sensitivity. 1. Ridgemoor Country Club 12th Fairway - Potential multiple tolerances to the DMI, dicarboximide, and benzimidazole chemistry classes. 2. Cantigny Experimental Green - Known tolerance to the DMI chemistry and resistance to the benzimidazole chemistry. 3. Prairie Landing Driving Range Target Green - No intensive fungicide applications over the years, so potentially no fungicide resistance issues. The products tested at each site include representatives of the benzimidazole, dicarboximide, and DMI classes, as well as newer fungicides such as the strobilurin products Compass and Insignia. Emerald, and Medallion which fall into other chemical classes, were also included. Of these, Emerald has excellent dollar spot activity, while Medallion, Compass, and Insignia have been reported to have 'suppressive' dollar spot activity. Emerald and Insignia are new products from BASF that have recently received EPA registration. Products, application rates/intervals, and mean disease severities for each site can be seen in Table 1, Table 2, and Table 3. Throughout the region, disease onset was much later than in previous seasons, and disease pressure was markedly lower. This is evidenced by no dollar spot symptoms showing in our plots until the beginning of August, whereas in years past a dollar spot explosion would normally occur in late May - early June. The shorter dollar spot season and lower disease pressure was potentially due to a colder 2003 winter and an almost non-existent spring that still had morning frosts in late May and June. At the Prairie Landing site, overall disease pressure was extremely low with the check plots only getting 5-8% dollar spot severity. Even with the low pressure, some differences in fungicide control were apparent. Most of the fungicides tested controlled dollar spot at an acceptable level. Medallion on a 14-day schedule also kept dollar spot at a somewhat acceptable level under a low pressure situation, which again supports the observed dollar spot suppressiveness of this product. The most notable result of this study was the ineffectiveness of Cleary's 3336, which is a representative of the benzimidazole class. This outcome shows that benzimidazole resistance may be a widespread characteristic of dollar spot populations in the Chicagoland area, which would render applications of these products useless for dollar spot control. At the Cantigny site, although again disease pressure was low, we could still tell some appreciable differences between the fungicides tested (see Graph 1). Bayleton, although on a site with known DMI resistance, worked fairly well at staving off dollar spot under low disease pressure. However, at the rates tested, we observed some phytoxicity in late August with season long use of Bayleton, which is probably related to the growth regulator effect of this DMI. The most notable difference in dollar spot suppression here was between the two strobilurin fungicides - Compass and Insignia. Insignia does seem to suppress dollar spot, holding it to under 1% severity, while Compass worked marginally, but did not provide an acceptable level of control. Emerald and the Emerald/Insignia alternating treatments, on the other hand, controlled dollar spot almost completely at both the rates and application intervals tested. At the Ridgemoor site, dollar spot pressure was more intense than at the other two sites, especially later in the season. As suspected, this site appears to have dollar spot populations with dicarboximide and DMI resistance (see Graph 2). Indirect evidence based on lab screens indicates that dicarboximide resistance may also be occurring at other sites in our region, so this was not a big surprise. The DMI sensitivity at Ridgemoor is less obvious this year, as Bayleton did suppress dollar spot to below 5%. At this site 10 years ago dollar spot resistance to the DMIs was much more prevalent. Since few DMIs have been used on these plots in those intervening10 years, this observation might indicate that DMI resistance comes at a fitness cost, and without the continued application of a DMI, the population may revert back to being DMI sensitive. Further study needs to be completed to verify this. The new Emerald and Insignia fungicides worked much the same way as at the Cantigny site, with Emerald providing complete control and Insignia having an incomplete, but suppressive effect on the disease (see Graph 3). One thing we noticed was that there was anthracnose present in the Emerald plots at both locations (Emerald is not labeled for anthracnose or brown patch), so an additional fungicide would need to be included in the regime to account for diseases not on the Emerald label. In conclusion, dollar spot has been found in Illinois and throughout the Midwest that is resistant or tolerant to the benzimidazoles, dicarboximides, and DMIs. Newer fungicides such as Emerald seem to be an effective tool for controlling these populations and should be rotated in with effective contact (multi-site inhibitor) products where a resistance problem is known to exist. Other new fungicides such as Insignia or Medallion, although only offering suppression and not complete control of the disease, could be used during times of low disease pressure to manage the disease until application of a fungicide labeled for dollar spot control is necessary. Thanks to our cooperators and supporters for these studies: Scott Witte, Supt., Cantigny Golf Club Pete Hahn, Supt., Ridgemoor Country Club Tony Kalina, Supt., Prairie Landing Golf Club Bayer (Ed Vandenburg and John Smith) Syngenta (Matt Geise and Jim Shone) BASF (David Oberle and Jeff Barnes) Table 1.   Fungicides and ratings for the Prairie Landing site.   Application Information Rating Dates & Mean % Dollar Spot Severity Fungicide Class Rates* Timing 7/25 8/1 8/8 8/15 8/22 8/29 9/5 9/12 Check --- --- --- 1.7 1.3 2.3 3.7 3.7 4.3 4.7 7 Banner DMI 1.0 21 days 0 0 0 0.3 0 0.7 1.3 1.3 Banner + Heritage DMI + stroby 1.0 + 0.2 21 days 0 0 0 0 0.3 0.7 0.7 2 Medallion phenylpyrrole 0.33 14 days 0 0 0.7 0 0.7 1 1.3 1 Medallion + Banner phenylpyrrole + DMI 0.33 + 1.0 21 days 0 0 0 0 0 0 0 0.3 Dac. + Banner multi-site + DMI 1.8 + 1.0 21 days 0.3 0.3 0 0 0 0.3 0 0 Dac.. multi-site 3.2 14 days 0 0 0 0 0 0 0 0 26 GT dicarboximide 3.0 21 days 0 0 0 0 0 0 0 0 Bayleton + Compass DMI + stroby 1.0 + 0.15 21 days 0 0 0 0 0 0 0.3 0.7 3336. benzimidazole 2.0 21 days 0.3 1.3 1.7 2.7 2.7 4.7 5 8.3 *Rates in oz/ 1,000 square feet   Table 2: Fungicides and ratings for Cantigny site.   Application Information Rating Dates & Mean % Dollar Spot Severity Fungicide Class Rates* Timing 7/7 7/14 7/21 8/4 8/11 8/18 8/25 9/2 Check --- --- --- 3.7 2.3 2.7 8 7.3 4.3 6.3 4.3 Compass stroby 0.15 21 days 3.7 1.7 3.7 5 6.3 2.3 3.7 3 Bayleton DMI 0.5 21 days 0.3 0.3 0 0.3 0.7 0 0 0 Bayleton DMI 1.0 21 days 0.3 0.7 0 0.7 0.3 0 0 0 Bayleton + Compass DMI + strobilurin 0.5 + 0.15 21 days 0.3 0 0.3 0.7 1.7 0 0.3 0 Bayleton + Compass DMI + strobilurin 1.0 + 0.15 21 days 0.3 0 0 0 0.3 0 0 0 Emerald anilide 0.13 14 days 0 0 0 0 0 0 0.3 0 Emerald anilide 0.18 21 days 0 0.3 0 0 0 0 0 0 Insignia strobilurin 0.9 14 days 0.3 0.3 0 0.7 0 0.3 0 0.3 Emerald / Insignia (alt.) anilide / strobilurin 0.13 / 0.9 14 days 0 0 0 0 0 0 0 0 Signature program ** various see below see below 0.7 0.7 0 0.3 0 0 0 0 26 GT/ Dac.+Sign (alt.) various 2.0/ 3.2 + 4.0 21/14 days 0 0 0 0 0 0 0 0 *Rates in oz/ 1,000 square feet ** Signature program: all applications contain 4 oz Signature in tank mix ... 1st app = Bayleton 1oz; 2nd app = Dac. Ultrex 3.2 oz; 3rd app = 26 GT 4 oz; 4th app = Bayleton 0.25 oz + Dac. Ultrex 1.8 oz; 5th app = Compass 0.15 oz + 26 GT 2 oz; 6th app = 4th app; 7th app = 5th app; 8th app = 2nd app; 9th app = 3rd app     Table 3: Fungicides and ratings for Ridgemoor site.   Application Information Rating Dates & Mean % Dollar Spot Severity Fungicide Class Rates* Timing 7/25 8/1 8/8 8/15 8/22 Check --- --- --- 3 7.3 7.3 8.3 26.7 26 GT dicarboximide 4.0 21 days 1.3 4 2 2 4.3 Curalan dicarboximide 1.0 / 2.0 ** 21 days 2.3 6 3 4.3 7.3 Dac. + 26 GT multi-site + dicarboximide 3.2 + 4.0 21 days 0.3 2 1 0.3 1.7 Dac. + Curalan multi-site + dicarboximide 3.2 + 1.0 21 days 0.3 3 1.3 0.3 3 Bayleton DMI 0.5 14 days 1.3 0.3 0.7 0.3 2 Bayleton DMI 1.0 21 days 0.3 1.7 0.7 0.7 2 Emerald anilide 0.13 14 days 0 0 0 0 0 Emerald anilide 0.18 21 days 0 0.7 0.3 0.3 0 Insignia strobilurin 0.9 14 days 0.7 0.7 1 0.3 0.7 Emerald / Insignia (alt) anilide / stroby 0.13 / 0.9 14 days 0.3 0 0.3 0 0 Dac. + Emerald multi-site + anilide 3.2 + 0.13 21 days 0 1 0.3 0 0 Compass + Bayleton strobilurin + DMI 0.15 + 1.0 21 days 0 1.7 0.3 0.7 3.7 *Rates in oz/ 1,000 square feet Graph 1: Efficacy of various fungicides on a DMI & benzimidazole resistant dollar spot population. Note: Rates in oz/ 1,000 square feet   Graph 2: Efficacy of various fungicides on a DMI, dicarboximide, & benzimidazole resistant dollar spot population. Note: Rates in oz/ 1,000 square feet   Graph 3: Efficacy of Emerald and Insignia on a DMI, dicarboximide, & benzimidazole resistant dollar spot population. Note: Rates in oz/ 1,000 square feet     For more information, e-mail newsletter@interactiveturf.com.