From a survey taken in Arkansas in the fall of 2020, 86% of respondents said they sighted resistant barnyardgrass in their rice fields. Widespread resistance from commonly used herbicides makes this weed hard to manage.
Tommy Butts, Extension weed scientist with the University of Arkansas System Division of Agriculture, discussed his 2021 recommendations for controlling barnyardgrass in rice production.
Butts spoke during the Arkansas online Rice Production Meeting, as a part of the 2021 Yield of Dreams Winter production meeting, which held sessions from experts on topics such as furrow irrigation and pest management.
Residuals, residuals, residuals
One management practice Butts' advocates for with barnyardgrass in rice acres is using residuals.
"One of the questions we asked in our survey was what percent of the time do our respondents fail to effectively control barnyardgrass with their first POST," Butts said. "We got a range of responses, but our average response was that 44% of the time the first POST herbicide application failed at controlling barnyardgrass."
The next question in the survey asked, If the initial herbicide application fails, how many additional applications are required to control it? Most respondents said it took three more applications to successfully control barnyardgrass.
"It is cause for concern that it takes us three more applications to successfully manage barnyardgrass, especially when we put costs to it," he said. "From our survey, the average cost to manage barnyardgrass was $87.45 an acre, which is 81% of total herbicide costs for the season as reported by our respondents. Barnyardgrass is a big deal cost-wise.
"The best control tip I can tell you for barnyardgrass is residuals, residuals, residuals."
Pre-emergence, residual herbicides overlapped 14 to 21 days (about 3 weeks) later with another round of residual herbicides are required. Also, make sure there is enough moisture to help guarantee activation.
"That length of time is the key to getting successful control of barnyardgrass season long," Butts said. "By overlapping Command followed by Prowl and Bolero in one of our test plots, we received excellent control from that sequential overlapping of residuals."
Also, Facet consistently showed in small plot research that it is better when used as a pre-emergent product, especially if mixed with Command upfront.
"One tank mix that works well is Command, Bolero, and League applied delayed PRE," Butts said. "This is an expensive mix, but across two of our sites within two years now, this has been my best tank mix for weed control, including barnyardgrass. I am not recommending it full scale across all your acres, but if you have a problematic field, I definitely recommend trying this. Although it is expensive upfront, it saved me at least one or two POST applications and ended up being a cheaper overall herbicide program because I got great residual control.
"As I mentioned, between what I gathered from survey results and discussions with producers and consultants, it seems that if we are ahead of the game and got residuals out, we had good control all season long. If we got behind with it and we missed that first application for barnyardgrass, it took three more applications to control it, and we normally ended up with fields that were a mess and got overrun because we could not play catch up. Using residuals effectively to our advantage is critical."