Golf Course Management

OCT 2015

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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10.15 GOLF COURSE MANAGEMENT 81 its respective growth chamber for zero, seven, 14 or 21 days in 2010. Because signifcant iprodione residues remained at 21 days after application in the 2010 trial, additional sampling dates of 28 and 35 days after application were added for both 2011 trials. Chlorothalonil fungicide analyses were conducted zero, seven, 14, 21 and 28 days after application in 2010 and in both 2011 trials. At each analysis date in both 2011 trials, two additional samples were taken from both iprodione- and chlorothalo - nil-treated feld plots. Samples were immedi- ately analyzed in the laboratory to compare fungicide depletion under feld conditions to depletion under growth chamber conditions. Concentrations of iprodione and chlo - rothalonil were analyzed using SmartAs- say ELISA kits purchased from Horiba Ltd. (Kyoto, Japan) (14,15). The kits were de - signed to detect trace amounts of fungicide on fresh produce heading to market, and we modifed the experimental procedure for use on golf course turfgrass (6). Time to 50% depletion (DT 50 ) was calculated by using a mathematical formula to approximate how many days it took for the fungicide to de - crease by half of its original concentration. Temperature results Temperature infuenced iprodione per- sistence during all three experiments (Figure 1). Iprodione DT 50 in 2010 was 8.98 days at 50 F, 6.73 days at 68 F, and 2.53 days at 86 F (Table 1). These results indicate that it took approximately nine days for iprodione to deplete to half of its original concentra - tion at 50 F, nearly seven days to reach 50% of the initial concentration at 68 F, and only 2.5 days to reach 50% of the original con - centration at 86 F. In other words, in 2010, iprodione depleted 3.5 times faster at 86 F than at 50 F. DT 50 values varied in both 2011 trials, but remained highest at 50 F and low - est at 86 F (Table 1). This temperature-based infuence may have important consequences for the use of iprodione in disease manage - ment. Typically, iprodione is reapplied every 14 to 21 days based on the fungicide manu - facturer's recommendation. Although these reapplication intervals are based on feld ef - fcacy trials, they do not account for varia- tions in environmental conditions. The rapid disappearance of iprodione at 86 F relative to 50 F suggests that iprodione protection is less persistent at higher temperatures and may leave plants susceptible to pathogen in - fection. Conversely, the increased persistence of iprodione at lower temperatures may allow for extended reapplication intervals beyond what the manufacturer recommends, lim - iting unnecessary chemical exposure to the environment and providing fnancial benefts to the superintendent. While temperature also infuenced the persistence of chlorothalonil on turfgrass leaf blades, the effect was less pronounced than it was for iprodione (Figure 2). Chlorothalonil DT 50 values were higher at 50 F than at either 68 F or 86 F, but DT 50 was actually lowest at 68 F in both 2011 trials (Table 1). Although the impact of temperature may be less consis - tent on chlorothalonil than on iprodione, it still has important implications for the use of chlorothalonil in disease management. Chlo - rothalonil reapplication intervals are also based on the manufacturer's label and are seven to 14 days on turfgrass. Based on the research presented here, however, chlorotha - lonil concentration observed 14 and 21 days after application on turfgrass exposed to 86 F was often half of the concentration observed on turfgrass exposed to 50 F. As was the case for iprodione, this suggests that higher tem - peratures may lead to increased potential for disease breakthrough as a result of increased chlorothalonil depletion. On the other hand, lower temperatures may extend the need to reapply chlorothalonil beyond the recom - mended interval. Despite the differences observed in the depletion of both fungicides, the specifc mechanisms responsible for the depletion re - main unclear. Iprodione is a localized pene- trant fungicide and is, therefore, absorbed into the leaf (7). Fungicides applied to leaf surfaces can take up to seven days to fully absorb into the leaf and, even then, upward of 50% of the fungicide may remain bound on the leaf surface (7). Once the fungicide has been ab - sorbed into the leaf, numerous plant defense responses may be released following exposure to iprodione and rapidly degrade the parent molecule (12). Increased plant metabolic ac - tivity at higher temperatures may provide a Year Iprodione Chlorothalonil Growth chambers Field Growth chambers Field 50 F (10 C) 68 F (20 C) 86 F (30 C) 50 F (10 C) 68 F (20 C) 86 F (30 C) 2010 † 8.98 ± 1.15 // 6.73 ± 0.56 2.53 ± 0.31 NA NA NA NA NA 2011a ‡ 27.7 ± 4.67 16.1 ± 1.54 3.30 ± 0.63 3.87 ± 0.94 16.8 ± 3.90 3.85 ± 0.95 7.96 ± 1.36 2.24 ± 0.34 2011b § 44.4 ± 8.94 5.37 ± 1.50 3.77 ± 0.93 3.98 ± 0.96 7.83 ± 2.70 4.33 ± 1.90 7.90 ± 4.53 2.25 ± 0.3 † Fungicides applied June 22, 2010; samples collected 0, 7, 14, and 21 days after application. ‡ Fungicides applied June 14, 2011; samples collected 0, 7, 14, 21, and 28 days after application with additional sampling for iprodione 35 days after application. § Fungicides applied Aug. 2, 2011; samples collected 0, 7, 14, 21, and 28 days after application with additional sampling for iprodione 35 days after application. // DT 50 values measured in days. Table 1. Time to 50% disappearance (DT 50 ) in days for iprodione and chlorothalonil from 50 F, 68 F and 86 F growth chambers following application to creeping bentgrass leaf blades maintained under fairway conditions. Samples in the growth chamber and feld samples were initially collected from the O.J. Noer Turfgrass Research Facility in Madison, Wis. Each value represents the mean of four replications. Days to disappearance for two fungicides

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