2018 and 2019 Field Experiments
Herbicides Rates and Timing
Experiments were conducted on ‘Alpha’ creeping bentgrass at the University of Nebraska-Lincoln and on ‘007’ creeping bentgrass at Ohio State Agricultural Technical Institute in Wooster, Ohio. Three CE rates were evaluated on either nontreated plots or plots first treated with bensulide (Bensumec 4 LF) at 318 fluid ounces per acre. Bensulide treatments occurred around early May each year and received 0.5 inches of irrigation immediately following application.
CE rates and timings intentionally differed by year. In 2018, CE rates were 2.0, 3.3 or 6.7 fluid ounces per acre at 0, 1, 3, 7, 14, 21, 35, 49 or 63 days after treatment with bensulide. Very minor phytotoxicity was observed and that was only when the highest rate of CE (6.7 ounces) was applied within three days after treatment with bensulide. Therefore, in 2019, a rate of 13.4 fluid ounces per acre of CE was included to simulate overapplication from excess spray boom overlap. Since no injury was observed at longer intervals, CE application dates were also altered to 0, 1, 3, 5, 7, 10, 14 or 21 days after treatment with bensulide to better observe differences among closer application timings.
Turfgrass quality (1 = dead turf; 6 = minimum acceptable quality; 9 = optimum turf quality) was estimated visually throughout the experiments weekly. Data from experiments were analyzed separately because of the changes to CE rates and timings in 2019.
Results
There were few differences in turfgrass quality in both the Nebraska and Ohio experiments in 2018 and the very minor differences in creeping bentgrass injury were largely dependent on the timing of CE applications. At both sites, minor injury was observed when CE was applied within three days after treatment with bensulide. When averaged over both sites and all CE rates and timings, at one week after treatment the quality of creeping bentgrass treated with bensulide was lower than bentgrass that didn’t receive bensulide. However, this minor injury was not visible by two weeks after CE treatment. Superintendents are typically aware of this transient injury from bensulide alone and find it to be insignificant, especially in light of the weed control benefits of the product.
Even though higher rates of CE were evaluated in 2019, turfgrass quality was again acceptable throughout the experiment in Nebraska. Only the timing of CE application affected turfgrass quality, which was generally a bit lower when CE was applied at 0 compared to 21 days after treatment with bensulide. The most-significant injury in these studies was observed in Ohio in 2019, when CE was applied at 13.4 fluid ounces per acre at 0, 1, 3, and 5 days after bensulide. No differences in creeping bentgrass quality were observed at rates of 2.0, 6.7 or 13.4 fluid ounces per acre of CE when bensulide had not been previously applied. The rates of 2.0 and 3.3 fluid ounces per acre of CE never reduced creeping bentgrass quality, regardless of timing or whether bensulide had previously been applied (Figure 1).
Turf quality ratings made one week after each of the eight CE treatment timings show that at 6.7 fluid ounces per acre, CE injured creeping bentgrass when applied 0, 1 or 3 days after treatment with bensulide (compared to plots that had not been treated with bensulide). Injury dissipated by three weeks after treatment. Similarly, the rate of 13.4 fluid ounces of CE injured creeping bentgrass one week after treatment when applied 0, 1, 3 or 5 days after treatment with bensulide (compared to plots that had not been treated with bensulide), and injury was still evident at two and three weeks after treatment when CE had been applied 0, 1 or 3 days after bensulide.
