The summer of 2023 posed significant challenges for turf management in the New England region, particularly in combating dollar spot disease. This was primarily due to elevated average humidity levels that persisted for an extended period compared to previous years. Analysis of summer weather data from Amherst, MA for the years 2022 and 2023 revealed a notable surge in humidity during 2023. In 2022, the average humidity for June, July, August, and September stood at 70%, 71%, 70%, and 79%, respectively. Conversely, in 2023, these figures notably escalated to 78%, 83%, 78%, and 85%, respectively. The most significant deviation occurred in July, witnessing a 12% surge in humidity compared to the preceding year.
Despite efforts to control dollar spot through repeated fungicide applications, effective management proved elusive during the unusually wet season. Various factors, such as fungicide resistance, improper application, and environmental conditions, contributed to this challenge. The heightened disease pressure led to an increased reliance on fungicides, resulting in numerous unsuccessful attempts at disease management and a surge in samples submitted for fungicide resistance testing. The frequent application of fungicides under favorable pathogen growth conditions not only increases the risk of selecting resistant populations but also leads to higher treatment frequencies and associated costs.
Based on the results of our in vitro fungicide resistance tests, conducted on isolates collected from sixteen golf courses spanning Connecticut, New York, Massachusetts, Vermont, Rhode Island, and West Virginia in 2023, it was observed that each population exhibited resistance or insensitivity to at least two fungicides with distinct modes of action. Seven out of the sixteen populations showed resistance to four fungicides with different modes of action, while two populations demonstrated resistance/insensitivity to all tested fungicides. Remarkably, all 97 isolates from these golf courses, irrespective of fairways, greens, or tees, displayed insensitivity to DMI fungicide. Surprisingly, despite this widespread insensitivity, ten, five, and five golf courses were still sensitive to SDHI, benzimidazole, and dicarboximide fungicides, respectively. These findings suggest that the challenges faced by some golf courses in controlling dollar spot are likely attributed to high disease pressures, while others may be due to multiple fungicide resistances, particularly to DMI and/or SDHI fungicides.
The critical issue requiring increased attention is the escalating unpredictability of weather conditions, which will increasingly complicate the prediction and management of dollar spot disease. As a proactive measure, it is advisable to conduct regular in vitro fungicide assays each year to monitor the pathogen population. This approach helps to minimize unnecessary and ineffective fungicide applications, allowing for the selection of potent fungicides for rotation or tank-mixing to delay the development of fungicide resistance. By adopting this strategy, you can safeguard your limited options for managing dollar spot disease, thereby preserving the health of your turf and your budget.
We sincerely wish your course continued success in the upcoming season.
Submitted by: Dr. Geunhwa Jung and Soonhong Min, Graduate Student, Jung Lab