Pest Management BMP March 2022

Thresholds of Resistance A threshold value must be established at every site (golf course), preferably using “indicator areas” where Dollar Spot becomes evident on untreated turf. Researchers suggest that susceptible turfgrass varieties have a threshold of 20%, while resistant varieties such as Declaration creeping bentgrass have a threshold of 40% (Zhang et al., 2021). However, it is best to have data that calibrate site-specific thresholds through observations. Once a threshold is established, monitoring of the model should occur routinely to assess risk of Dollar Spot infections. When the Smith-Kerns model exceeds the threshold, a pesticide can be applied. It can be assumed that the treated fairway turf will not experience disease until the fungicide interval expires, typically between 14 and 28 days. Once the interval lapses, the model is once again consulted to see if threshold levels are still exceeded, and the process repeats. A common critique of this system is the flexibility it requires in timing of pesticide applications. In most cases, facilities are constrained in the days they can apply chemical products (e.g., Monday), and therefore may not be able to apply treatment when the model based approach necessitates. In these cases, it may be appropriate to round the model-based date to the closest available day. Consideration can be made to the slope of the model line when rounding. For example, an interval may run out on a Thursday where the model projects pressure to be above threshold but following a downward trend. In this case, application could be delayed until the following Monday. Conversely, if the pressure was following an upward trend, a preventative application on the Monday prior may be warranted. Assessing Pest Management Costs Some managers question if this model-based approach will achieve the same results as a preventative program, i.e., high quality disease-free fairway turf. Fortunately, research at University of Wisconsin-Madison over the last three years shows that various model-based approaches provide equal results to a preventative program both in turf quality and disease suppression (Melton et al., 2019, Melton et al., 2020, Fenner et al., 2021)). It follows then that golf operations would be interested in cost savings associated with a risk model based approach to Dollar Spot control.

A recent analysis of pesticide use on golf courses in New York showed that pesticide applications made to fairways contributed the most pesticide risk of any playing surface (Bekken et al., 2021). Putting greens receive more pesticide use on a per area basis but, fairways cover more land and therefore require larger quantities of pesticide use, thereby increasing cost and risk. In New York, the most common and troublesome pest affecting finely mowed golf course areas is the fungus Clarireedia jacksonii , commonly known as Dollar Spot. Traditionally, routine, frequent fairway fungicide applications are made preventatively for Dollar Spot control on fairways throughout the season. Often this can result in as many as eight applications to an average 30 acres of turf or 240 total treated acres. Furthermore, routine frequent applications assume there is persistent disease pressure when studies have shown pressure fluctuates throughout the season. This results invariably in over-applying material. Transforming Treatment Strategy A preventative approach is an effective way to control Dollar Spot however, it is excessively risk averse. Preventative approaches do not consider the variability in Dollar Spot emergence as weather conditions change. Therefore, it is highly likely that pesticide applications are made during times when Dollar Spot is not active. The result is unwarranted pesticide use that increases cost and environmental risk. To reduce unnecessary pesticide use without compromising turf quality, Superintendents have a variety of options, two of which are: strategically withholding pesticide applications when pest pressure is predicted to be below threshold, and planting disease resistant turfgrass species that require fewer pesticide applications. In recent years, turfgrass researchers have sought to address the inherent issues with preventative management programs by creating disease forecasting models. These models use temperature and relative humidity data from weather stations to assess and predict disease pressure to guide pest management decision-making. The popular and verified Smith Kerns Dollar Spot Prediction Model, estimates the likelihood of Dollar Spot outbreaks and has been calibrated through field research across the United States. It is available for free online at: https://www. greencastonline.com/dollar-spot-solutions

Pest Management BMP Reducing Risk with Data Driven Fairway Pest Management

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