Research Report
Using HPPD-Inhibiting Herbicides for Goosegrass Control in Bermudagrass Virginia Tech Researchers: John R. Brewer, M.S. Student, Michael C. Cox, Graduate Research Assistant, Sandeep S. Rana, Doctoral Student, and Shawn D. Askew, Ph.D., Associate Professor and Extension Turfgrass Weed Specialist
F
ew postemergence herbicide options exist for goosegrass (Eleusine indica) control on bermudagrass turf. Recent restrictions on MSMA have rendered the longstanding combination of MSMA plus metribuzin ineffective since turf managers can no longer treat enough area or enough times to effectively address goosegrass infestations. Now, the loss of diclofop has further limited postemergence control options in bermudagrass. Most turf managers are using multiple treatments of foramsulfuron and sulfentrazone, but these herbicides are expensive and effective only on seedling goosegrass. Recent turfgrass registration of the HPPD-inhibiting herbicides mesotrione (Tenacity) and topramezone (Pylex) has led to attempts to achieve selective goosegrass control in bermudagrass with these new herbicides. Topramezone, in particular, effectively controls large goosegrass plants at half the maximum use rate in cool-season turf. At rates as low as 7% of the maximum labeled rate, topramezone can control seedling goosegrass. Unfortunately, bermudagrass turf is typically injured by topramezone.
Our Research
At Virginia Tech, we have been evaluating potential topramezone programs for goosegrass control in bermudagrass since 2012. Two green-house trials were conducted in 2012 and 2013 to evaluate various rates of topramezone in combination with several rates of triclopyr (Turflon Ester) for goosegrass control and bermudagrass response. In 2013 and 2014, topramezone at 0.25 and 0.5 oz./A was applied alone or in mixture with triclopyr at 4 oz./A on 31 cultivars of bermudagrass maintained at a 1.25" mowing height. In 2014, two trials were conducted to evaluate goosegrass control and bermudagrass response to topramezone at 0.1 and 0.2 oz./A applied weekly with and without triclopyr at 1 oz./A.
Research Results
Greenhouse studies in 2012 and 2013 suggested that topramezone at 0.25 and 0.5 oz./A and triclopyr at 4 oz./A represented the best balance between bermudagrass safety and goosegrass control. These rates were used in subsequent field trials in 2013 and 2014 to evaluate bermudagrass
Response of 31 bermudagrass cultivars to topramezone (Pylex) applied at 0.25 or 0.5 oz./A alone or mixed with triclopyr (Turflon Ester) at 4 oz./A. Bronze plots contained Turflon, and white plots are only Pylex. Photo taken 21 days after treatment.
cultivar response and goosegrass control. At three trial sites, goosegrass cover ranged from 19% to 37 %. By 10 weeks after initial treatment (WAIT), topramezone at either rate alone or with triclopyr reduced goosegrass cover to between 0% and 7%. All bermudagrass cultivars were injured 30% to 70%. White symptoms from topramezone alone persisted for at least two weeks. Necrotic symptoms from triclopyr combinations ranged between 20% and 40% but persisted for as long as 5 weeks. Despite the initial greenhouse results, field studies suggest that lower rates of triclopyr may be more effective. The treatments of topramezone alone at 0.1 and 0.2 oz./A injured bermudagrass 41% and 16%, respectively at 7 WAIT. These studies suggest that HPPDinhibiting herbicides may be more injurious to bermudagrass in Virginia than has been reported from states further south. In addition, low use rates of topramezone can effectively control goosegrass in bermudagrass, but severe bermudagrass injury may persist for two weeks or more. c
At 28 days after treatment, almost all Pylex plots have recovered, but the bronze color and stunting of plots treated with the Turflon + Pylex mixture is still persisting. Future work will use lower rates of Turflon.