Rice can be a beautiful crop. Those green rice plants growing out of blue water laced with gracefully curving levees (at least in older, conventional fields) can be a pleasing site in the middle of a hot Midsouth summer.
But those floodwaters serve another purpose – weed suppression – and when they’re scaled back, as in furrow-irrigated or row rice, farmers may need to step up their herbicide program to compensate.
“We need to expect this could take a minimum of three herbicide applications, but, more likely, it may take four,” said Dr. Tommy Butts, Extension weed scientist with the University of Arkansas System Division of Agriculture. Butts spoke on rice weed control at the Arkansas Rice and Soybean Online Field Day.
“And, in each of those applications, we will need to tank mix multiple herbicides to get season-long control such as in this plot right next to me here,” he said, speaking from the University of Arkansas Pine Bluff’s Small Farm Outreach Center near Lonoke, Ark.
The test plots in the study demonstrate several “takeaways”, he said, including the critical nature of the overlapping and timing of residual and postemergence herbicides in row rice.
“We need the second treatment at 14 days after our initial residual application,” said Butts. “They also show the importance of selecting herbicides to manage the weed species that we have in our row rice fields.
“In these plots, we have a heavy population of barnyardgrass, a bad crabgrass population, a little bit of coffeebean and some sedges – a pretty good rice flatsedge population and a few yellow nutsedges sprinkled in here and there. So you need to select postemergence products that are effective on that diverse weed spectrum and overlap the residual herbicides.”
He discussed how one of the cleanest plots in the study followed those guidelines, starting with a pre-emergence application of Command plus Sharpen.
“That gives us grass control, broadleaf residual control and a little bit of flatsedge residual control with the Sharpen,” he noted. “Facet or Quinclorac may also be a good option to mix into that pre. I like moving Quinclorac up as a residual to give us good activity on flatsedge.”
The next application, 14 days later, was Preface and Gambit plus Command to overlap the initial Command residual.
“Again, that 14-day timing is critical,” he said. “At that point we added a postemergence product to kill any grass that was up. We got a little more residual from Preface, but we also got some post activity from that as well. Gambit provided postemergence activity on our sedges, a bit of residual on sedges, and it takes out our coffeebean or hemp sesbania.”
For the third application, which was made between 14 to 21 days later when the rice was reaching four to five leaves or pre-flood timing, the plot received a shot of Preface along with a broadleaf herbicide material.
“In this case, it was Aim, but you could implement a number of different options,” he noted. “If you haven’t used it earlier, you could use Gambit. You could also use something like Ultra Blazer, or you could go to Loyant, which is good for a lot of broadleaf weeds.”
The plot Butts was discussing did not have many Palmer amaranth seedlings, which can often be a problem in row rice or levee rice.
“If you have a bad Palmer population, which we normally do in our row rice acres, you will definitely want to use Loyant at some point in your three applications,” he said. “And you may want to think about Grandstand and Propanil. I like to see Grandstand and Propanil in that second herbicide application when our pigweeds may be small. The burning action of propanil is good on small pigweeds.
“If nothing else, it will burn some bigger pigweed back and give you more time for that Loyant application. When you come back for that third timing, if they're six to eight inches or less, we can drop our rate of Loyant to eight ounces and still be successful.”
What happens if you delay the second herbicide application from the recommended 14 to 21 to 28 days? “If we did that, we had escapes, and we weren’t able to get them under control or get enough of the next flush killed. We ended up with yield losses.”
In another set of plots, the researchers applied the residual, overlapping herbicide in 14 days, but did not add a postemergence herbicide to manage weeds that had already come out of the ground.
“So we had some breakthroughs, and we did not get those under control. Even though we overlapped residuals, we just didn't get anything that was up, and we had escapes of sedges and a few barnyardgrass. That’s why it’s critically important to closely scout our row rice acres.”
To watch Butts’ presentation, visit Weed Control in Rice: Pre-Emergence Residuals, Row Rice, Upcoming Research (uada.edu).