As rice begins to mature, some Arkansas farmers are finding symptoms of damage from Roundup herbicide drift. The damage potential is great, according to Bob Scott, weed scientist with the University of Arkansas Cooperative Extension Service.
“Even low levels of drift can cause as much as a 50 percent or more yield reduction in rice,” he said. Last year, the statewide average rice yield was a record 6,440 pounds per acre.
“Arkansas has so much more rice than other states that we seem to have the lion's share of the drift problem,” Scott noted.
The problem is caused by Roundup herbicide or other products containing glyphosate, Roundup's active ingredient, being sprayed on soybean fields and drifting over to adjacent rice fields. It happens when rice has reached the reproductive stage and becomes sensitive to the herbicide.
The majority of Arkansas' 2.9 million acres of soybeans has been genetically modified to tolerate Roundup, Scott said. The 1.4 million-acre rice crop, however, has no tolerance to the herbicide.
“Farmers will begin noticing the problem when rice starts to head. Symptoms don't show up well until then.” He said the heads will be deformed or blank, and the flag leaf, or topmost leaf, will be reduced in length by as much as two-thirds.
“Unfortunately, this year, we had a lot of soybeans that needed to be sprayed at the same time rice was in the reproductive stage because a lot of beans were planted later. So we have more potential than usual for a lot of drift damage.”
Scott said farmers may think they're seeing straighthead disease symptoms when they're really seeing symptoms of Roundup or glyphosate injury. Some farmers are surprised because they've not had straighthead before. A glyphosate-damaged field appears to be stunted because of the small flag leaf. With straighthead disease, the flag leaf is normal. The grain in a glyphosate-damaged plant either never forms or is twisted, a condition commonly called fish-hooked or parrot-beaked.
“The drift problem is pretty much all over the Arkansas Delta,” Scott said. “Anywhere Roundup Ready soybeans are grown next to rice there is the potential for drift.”
The prognosis is not good. There's nothing farmers can do to correct the damage once it's done, Scott said. He said they're left with trying to determine how the mishap occurred and where fault lies.
Scott said glyphosate drift is becoming more of a problem, and many farmers are becoming familiar with it because of personal experience.
Jeff Branson, Extension rice verification program coordinator, said he saw a considerable amount of Roundup drift damage to rice last season. “Usually there's a soybean field sitting beside every rice field. If you get drift before it goes into the reproductive stage, you may not see any yield reduction.”
He said Roundup drift from soybeans fields aren't the only problem source. About 80 percent of Arkansas' 950,000 acres of cotton is Roundup Ready-tolerant.
Branson said, “The main thing is to watch the wind. Most drift problems are caused by applying herbicides when it's too windy.”
Lamar James is an Extension communications specialist with the University of Arkansas.