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Utilizing Modeling for Effective Dollar Spot Control

Dollar Spot

Dollar spot is a widespread disease of fine turf caused by the Sclerotinia homoeocarpa pathogen and can infect turf all across the country but is most prevalent in southern Ontario and Quebec from May until October. Since the disease can be active for an extended period of time the fungal population can be very high by the latter months of the season, leading to especially devastating outbreaks in the warm, late-season days that can have heavy dew to exacerbate an outbreak. In order to keep the population from elevating quickly it is important to begin control at an optimum time, not trying to control the pathogen ‘early’ but rather beginning to control the fungus at the appropriate time - when the fungus is actively growing but prior to the expression of symptoms. Once dollar spot symptoms are apparent, which is late in the disease cycle, population has elevated to numbers that could make dollar spot control challenging for the remainder of the season.

Utilizing Modeling for Effective Dollar Spot Control

Reducing the fungal population to the lowest levels can be accomplished by utilizing an effective environmental model to determine the most appropriate time to apply the fungicide. The model developed at the University of Guelph (Nailor, 2000) tracks the number of days where the average temperature [(High + Low)/2] is greater than 16 °C. When the 10th such day is reached then dollar spot symptoms can be expected to be found on susceptible turf. Typically, this threshold is reached in mid-May or June. Tracking should therefore begin in late-April or the first of May.

Naturally, there are exceptions to the model; some areas remain warmer than others and symptoms can be delayed or appear earlier depending on the specific micro-climates and the source of the weather data being used. Each turf manager will be able to determine how the model is best deployed on the property. The goal of using the model is to target the fungus when it is actively growing but before the disease is apparent. Therefore, the weather forecast should be analyzed to see if the model parameters will be met in the coming week. If so, the fungicide application should occur before the model is triggered, thereby preventing symptom development and reducing the pathogen population when numbers are still low.

There is also a component of the ‘art’ of managing Turfgrass in determining when to begin tracking days. Occasionally, there will be a day that has an average mean temperature in excess of 16 °C when the snow is melting or the turf is still dormant. Typically that day is not tracked but each manager can make their determination of how
impactful these ‘outlier’ days are in the development of the dollar spot fungus. Also, the time at which the chemical control begins is a function of how much safety margin that the individual manager would like to build in to the model, the closer to the end of the model, the greater the risk that the model will have triggered and dollar spot symptoms will be apparent in warmer micro-climates. Some managers may wish to wait as long as possible and make their control application while some will prefer to make it on day 6 or 7.

Dollar Spot Control Options from Syngenta:

Banner Maxx® at 26-51 mL/100 m2
Concert™ at 100-225 mL/100 m2
Civitas™ at 250-500 mL/100 m2 + Banner Maxx® at 26-51 mL/100 m2
Daconil® Ultrex at 58-212 g/100 m2
Daconil 2787® at 95-350 mL/100 m2
Velista™ at 9-15 g/100 m2

For more information on products, rates and control strategies, check out: GreenCast.ca or download the GreenCast TurfApp from the App store® or Google Play™.