Golf Course Management

SEP 2014

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82 GOLF COURSE MANAGEMENT 09.14 the previous fall. To obtain >90% control six months later, two applications of Dismiss South 4 SC at 7.2 ounces/acre (0.53 liter/hect - are) plus either Tribute Total at 3.2 ounces/ acre (224 grams/hectare) or Xonerate 4 SC at 7.25 ounces/acre (0.53 liter/hectare) provided this. The three-way combination of these products also provided excellent tropical sig - nalgrass control but was similar to the listed two-way combination treatments. In a study examining two fall applications of Xonerate alone or with Tribute Total, 10 and 14.5 ounces/acre (0.73 and 1.05 liters/ hectare) of Xonerate 4 SC provided >90% tropical signalgrass control the following May while lower rates (5 and 7.25 ounces/acre [0.37 and 0.53 liter/hectare]) did not (Table 4). The combination of Xonerate at 7.25 + Tribute Total at 3.2 ounces/acre applied twice in fall also provided excellent tropical signal - grass control the following spring. Additional studies were performed to de - team and typically involved irrigating to avoid drought, 4 pounds of nitrogen/1,000 square feet (19.5 grams/square meter) applied yearly, mowing at 0.75 inch (1.9 centimeters), and no overseeding. From this initial screening, fve candidates emerged: Tribute Total, Xon - erate, Dismiss South, Revolver and, possibly, Celsius. The next step was to narrow down optimal application timings and rates, compare single versus sequential applications and evaluate possible treatment combinations. Studies were implemented to compare fall versus spring ap - plication timing, to identify the ideal num- ber of applications, to determine if addition of ammonium sulfate (21-0-0 at 1.5 pounds product/acre [1.68 kilograms/hectare]) to her - bicides enhanced control, and to screen addi- tional possible alternative herbicides. Bermu- dagrass phytotoxicity (%) was rated visually, and tropical signalgrass control was calculated from line-intersect counts from a 3- × 3-foot (0.9- × 0.9-meter) grid randomly placed in each plot. Application timing/number After our initial screening, we began focus - ing on products showing the most promise. Tribute Total was identifed as one of these; thus, we started examining the number of ap - plications necessary to provide >90% control. Our frst study in spring 2013 determined four applications were needed to provide this level of control (Table 1). As the season progressed, only the fve-application regime was able to provide this level of control. The label currently allows broadcast applications to total 6.4 ounces/acre (448 grams/hectare) throughout a growing season. However, spot treatments are allowed beyond that, using 0.073 ounce of product per gallon of water (8.0 grams/liter), treating weeds until they are wet, and only spot-treating up to one-quarter of the entire infestation area. For example, treatment of up to 10,000 non-continuous square feet per acre (2,295 square meters/ hectare) is considered a "spot treatment." When similar treatments were applied in the fall, tropical signalgrass control >90% was obtained the following spring with only two Tribute Total applications (Table 2). Excel - lent control remained six months after the last fall application. Additional studies were conducted exam - ining the effcacy of fall applications with other products. Table 3 lists tropical signal - grass control in spring following applications Tropical signalgrass control in 2014 after fall 2013 treatments Treatments † Rate (ounces/acre) Treatment timing, 2013 % TSG control, 2014 May 5 ‡ June 9 Nontreated − − 0 c § 0 e Xonerate 4 SC 5 Sept. 23 fb Oct. 7 40 c 25 d Xonerate 4 SC 7.25 Sept. 23 fb Oct. 7 76 ab 70 c Xonerate 4 SC 10 Sept. 23 95 a 88 abc Xonerate 4 SC 14.5 Sept. 23 94 a 92 ab Xonerate 4 SC + Tribute Total 60.5 WDG 7.25 + 3.2 Sept. 23 fb Oct. 7 100 a 98 a Tribute Total 60.5 WDG 3.2 Sept. 23 fb Oct. 7 79 a 76 bc † Treatments: Sept. 23 and Oct. 7, 2013, in 40 gallons/acre. Methylated seed oil was added at all treatments at 0.5% v/v. ‡ No bermudagrass phytotoxicity was recorded with any treatment. § Values in a column not followed by the same letter are significantly different. Table 4. Tropical signalgrass (TSG) control in 2014 following fall 2013 treatments with Xonerate and Tribute Total. One of many study sites with heavy tropical signalgrass infestation (the light green grass) in a bermudagrass fairway.

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