Golf Course Management

MAY 2019

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64 GOLF COURSE MANAGEMENT 05.19 see growing at a rate of 0.08 to 0.09 inch (0.20 to 0.22 cm) per day, compared with only 0.06 inch (0.15 cm) per day for those collected from golf courses in West Tennessee. Non-selective herbicide response Neither region, golf course type, nor turf species affected survival after glyphosate ap - plication. However, 20% of the biotypes tested screened positive for resistance (>30% survival), while only 36% fell into the suscep - tible grouping (< 5% survival). The remain- der were intermediate, indicating some level of glyphosate resistance was present within the population. In total, these data indicate that 64% of the annual bluegrass on Tennes - see golf courses included in this survey is (or is becoming) resistant to glyphosate. Biotypes also differed in response to glu - fosinate and diquat. It should be noted that annual bluegrass treated with these herbicides often exhibits rapid necrosis and recovery after treatment. This effect was observed in our study and could explain the variability in sur - vival observed among biotypes. This survey of annual bluegrass from Ten - nessee golf courses is still ongoing, with popu- lations being screened against other pre- and post-emergence herbicides during 2019. Re - cent work includes screening these populations for resistance to prodiamine and foramsulfu - ron, as well as other modes of action. Literature cited 1. Owen, M.J., M.J. Walsh, R.S. Llewellyn and S.B. Powles. 2007. Widespread occurrence of multiple herbicide resistance in Western Australian annual ryegrass (Lolium rigidum ) populations. Australian Journal of Agricultural Research 58:711-718. James T. Brosnan (jbrosnan@utk.edu) is an associate professor in the Plant Sciences Department at the Uni - versity of Tennessee–Knoxville and heads the university's Weed Diagnostics Center and the turfgrass weed science research and Extension program. José Javier Vargas is a research associate with the Turf and Ornamental Weed Science program at the university and the head diagnosti - cian at the Weed Diagnostics Center. Greg K. Breeden is a weed science Extension assistant at the university and manages the university's turfgrass weed science field research. (report) Dollar spot control using urea and iron sulfate Kurt Hockemeyer, M.S. Chase Straw, Ph.D. Brian Horgan, Ph.D. Doug Soldat, Ph.D. Paul Koch, Ph.D. Dollar spot is the most economically im - portant disease of golf course turfgrass, and insufficient cultural control measures have led to a heavy reliance on repeated use of fun - gicides. Iron sulfate (FeSO 4 ) has been used for decades in the turfgrass industry for its ability to improve turfgrass color (3). Recent research out of Oregon State showed that FeSO 4 can provide excellent control of Mi- crodochium patch when applied at regular two-week intervals (1). In addition, research - ers from Virginia Tech demonstrated that FeSO 4 can also provide significant reduc- tions in dollar spot on a creeping bentgrass putting green when applied at high rates (1 pound/1,000 square feet; 48.8 kilograms/ hectare) every two weeks (2). However, in both cases, the FeSO 4 injured the putting surfaces to an unacceptable level after re - peated applications. e objectives of this study are to determine the impact of FeSO 4 and urea, both alone and applied as a tank Impact of iron sulfate vs. non-treated turf at the O.J. Noer Turfgrass Research Facility in Madison, Wis., on July 18, 2018. Photo by Paul Koch mixture, on the development of dollar spot; and to identify the appropriate reapplication interval and water volume that provide ef - fective dollar spot control and optimal turf quality. Study design Separate studies were conducted for each objective listed above, and both studies were replicated at the O.J. Noer Turfgrass Re - search and Education Facility in Madison, Wis., and Minnesota Valley Country Club in Bloomington, Minn. All Wisconsin treat - ments were initiated on May 17, 2018, and all Minnesota treatments were initiated on May 23. Subsequent applications were made at 7-, 14-, 28-, or 42-day intervals. A full list of treatments for both studies can be found in Tables 1 and 2. Year 1 results Objective 1. Treatments containing iron sulfate generally reduced dollar spot relative to the non-treated control at both locations Nontreated Iron sulfate, 6 ounces, 7-day interval, tank mix: 1.5 gallons water

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