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  • Dollar spot is one of the most economically important diseases for golf courses around the world.
  • Traditional fungicide application programs are preventive on calendar-based intervals or curative whenever symptoms appear.
  • Calendar-based fungicide applications were compared to scheduling based on a dollar spot forecast model and threshold-based applications on several bentgrass cultivars with varied levels of dollar spot susceptibility.
  • Threshold-based fungicide applications on bentgrass cultivars with low disease susceptibility provided excellent disease control and reduced fungicide applications.
  • Model-based or calendar-based applications were required for good dollar spot control on highly susceptible bentgrass cultivars. Model-based applications offered a moderate reduction in fungicide applications.

Outbreaks of dollar spot infect all cool-season grasses and can be challenging and costly to control. Traditional fungicide control methods involve repeat calendar-based applications when the dollar spot pathogen is expected to be active or curative applications when outbreaks occur. This approach can lead to unnecessary applications that increase cost and increase fungicide resistance potential. Conversely, if too few or poorly timed applications are made, dollar spot outbreaks can quickly produce unacceptable playing conditions. Researchers at Rutgers University have looked at controlling this disease more effectively with weather-based predictive modeling that determines when dollar spot occurrence is likely to be greatest, and by using bentgrass cultivars that are more tolerant of this problematic disease.

Two three-year field trials using six bentgrass cultivars were conducted. The six bentgrass cultivars were selected based on dollar spot susceptibility. Ranging from most to least susceptible, the cultivars used were ‘Independence’, ‘Penncross’, ‘Shark’, ‘007’, ‘Declaration’ and ‘Capri’. Capri is a colonial bentgrass, whereas the other cultivars are creeping bentgrasses. The first trial used growing degree day (GDD) and weather-based models to predict the onset of dollar spot incidence on the bentgrass cultivars. The second trial examined the effect of fungicide application timing on dollar spot incidence on bentgrass cultivars with low and high dollar spot susceptibility – ‘Declaration’ and ‘Independence’, respectively.

Bentgrass cultivars with low susceptibility to dollar spot exhibited delayed initial onset of disease symptoms for 4 to 27 days, compared to highly susceptible cultivars, but neither GDD or weather-based modeling consistently predicted the initial onset of symptoms early in the season. Predicting disease outbreaks in-season using the model was not reliable on the cultivars with low dollar spot susceptibility, but outbreak was accurately predicted with less-tolerant cultivars.

When assessing both the model- and threshold-based fungicide application timings – i.e., fungicide application made at first appearance of disease symptom – excellent disease control was achieved with each treatment regime on the low-susceptibility cultivar (‘Declaration’). However, the bentgrass cultivar with high disease susceptibility (‘Independence’) required model-based fungicide applications for effective control.

The results of this study suggest dollar spot can be effectively controlled with a threshold-based approach on bentgrass cultivars with low disease susceptibility. This program offers excellent control and reduced fungicide use for these cultivars. Conversely, dollar spot can be effectively controlled on highly susceptible bentgrass cultivars with fewer fungicide applications using model-based applications. It should be noted that this study only evaluated the extremes of cultivar susceptibility, and further assessment with intermediate susceptibility is needed.