Virginia Turfgrass Journal - July / August 2017

Page 20

Feature Story

Incorporating FERROUS SULFATE into Your Dollar Spot Suppression Program By Camden D. Shelton, M.S. candidate; David S. McCall, Ph.D., Turfgrass Pathology; Erik H. Ervin, Ph.D., Turfgrass Scientist; and Shawn D. Askew, Ph.D., Weed Scientist, Virginia Tech


esearchers at Virginia Tech first demonstrated in 2012 that ferrous sulfate (20% ferrous sulfate-heptahydrate) applied at 1 lb./1,000 ft2 can reduce dollar spot pressure without traditional fungicides. This strategy has not been widely adopted, largely because of the excessive rates and unknown impact on the turfgrass system over time. Because previously tested ferrous sulfate rates were so high, trials were established to determine if lower rates could also provide desired control. Studies were conducted at the Virginia Tech Turfgrass Research Center in Blacksburg, VA, in 2016 on a ‘007’ creeping bentgrass (Agrostis stolonifera) putting green and an ‘L-93’ creeping bentgrass fairway. Ferrous sulfate was applied at five rates (0, 0.1, 0.5, 1 and 2 lbs. /1,000 ft2) every 14 days and evaluated weekly for its ability to reduce dollar spot. After one season, our data suggest that rates can be reduced to 0.5 lbs.

/ 1,000 sq. ft. without compromising efficacy. The reduction was evident on both green and fairway trials, but this research needs to be repeated to validate our findings. While this research shows potential as a management option, it was apparent that this strategy alone would not be sufficient for acceptable control. Therefore, we have begun investigating how the use of ferrous sulfate may impact a chlorothalonil fungicide program. Our data suggest that ferrous sulfate can extend the longevity of dollar spot control with chlorothalonil (3.6 fl. oz. /1000 ft2 Daconil WeatherStik) by 5 days. Chlorothalonil reapplication interval was extended from 11 and 9 days without ferrous sulfate to 16 and 14 days when ferrous sulfate was applied on fairways and greens, respectively. In conjunction with our trials on extending chlorothalonil longevity, we investigated how ferrous sulfate can reduce the total amount of chlorothalonil

Dollar spot suppression with ferrous sulfate (FeSO4) applied at 0 lb. (untreated control-top).

needed to maintain dollar spot below an acceptable threshold. Chlorothalonil treatments were applied as follows: 0, 1, 2, 3 and 4 fl. oz. /1000 ft2 of Daconil WeatherStik across plots treated with and without ferrous sulfate applied every other week. To date, the addition of ferrous sulfate has shown a substantial reduction in the amount of chlorothalonil necessary to maintain dollar spot below an acceptable level, but the reduction appears to be largely based on disease pressure. During mild infestations, the rate of chlorothalonil needed should be significantly lower than during a more severe outbreak when accompanied with ferrous sulfate. This research may help turf managers adhere to annual site-use limitations of chlorothalonil while still achieving acceptable dollar spot control throughout the season. This article previously appeared in the March 2017 issue of Golfdom magazine.

Dollar spot suppression with ferrous sulfate (FeSO4) applied at 0.5 lb. per 1,000 ft2 on a 007 creeping bentgrass putting green.


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