Impact of light-weight rolling and ferrous sulfate applications on creeping bentgrass fairways

By Travis Roberson, Kevin Hensler, and David McCall, Ph.D.

Dollar spot is one of the most common diseases that turf managers struggle with managing on cool-season grasses in the mid-Atlantic region. More money is spent to control this disease than any other because of the frequency of fungicide applications. Researchers have focused on a variety of strategies to reduce dollar spot; some of which include cultural practices while others rely on chemistries. Two such strategies include the use of inexpensive ferrous sulfate and the use of light-weight rolling on putting greens. However, the use of fairway rollers across larger acreage is still a new concept to many. Our team explored these strategies together to reduce dollar spot pressure on golf course fairways.

The objective of this study was to examine the impacts of ferrous sulfate applications and light-weight rolling on dollar spot development and overall turf quality of creeping bentgrass fairways. This experiment was repeated twice (summer 2017 and 2018) and carried out on a ‘L-93’ creeping bentgrass (CBG) fairway at the Glade Road Research Facility in Blacksburg, VA. The site had moderate to high amount of thatch accumulation, which typically promotes dollar spot development. The study was initiated in early summer and concluded in September. The trail was organized into a 3x2 factorial design and blocked by rolling amounts with split-plot ferrous sulfate applications. A Smithco Ultra-Lite greens roller applying approximately 20 kPa of ground pressure was used for rolling 0, 1, 2 d -1 wk -3 (0x, 1x, and 2x). Ferrous sulfate (FeSO 4 ) was applied on 14-day intervals at a rate of 0.5 lbs product/1000ft 2 based on previous research at VT. Turf quality (TQ where 9 = highest quality and 6 = minimally acceptable), dollar spot percent (DS %), and dollar spot infection center counts (DS IC ) were assessed weekly throughout the study. Turf quality data were transformed to standardized area under the progress curve (SA UTQPC ) values while DS % and DS IC were converted to area under the disease progress curve (AUDPC ). Fit least squares analysis and analysis of variance based on transformed values were completed through JMP Pro 13 (Cary, NC ) statistical software. Higher dollar spot pressure was seen within the 2017 trial and therefore two rescue applications of chlorothalonil were made on July 24th and August 5th.

Dollar spot development

Overall, dollar spot was reduced by approximately 50-70% with both ferrous sulfate applications and 2x lightweight fairway rolling. Turf quality and DS IC data from both years were pooled together for analysis, while DS % data were analyzed separately by year. Dollar spot IC were reduced by both ferrous sulfate applications and 2x light-weight fairway rolling. However, single rolling three times per week did not reduce dollar spot. Ferrous sulfate reduced DS % in each year but rolling did not. Turf quality was increased by ferrous sulfate applications but not with rolling. Based on our results and the associated costs and labor associated with each strategy, we recommend suppressing dollar spot with ferrous sulfate more so than with light-weight fairway rolling. However, dollar spot cannot be completely eliminated with one strategy alone, including the use of fungicides. Each of these methods provide another tool in the turf manager’s belt to help fight the battle against such a persistent disease.