Pay attention to wind, several other factors to minimize off-target herbicide movement onto sensitive crops.
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By Vicky Boyd
As growers of other row crops have transitioned away from glyphosate because of resistance concerns, the timing and extent of herbicide drift damage to rice also has changed.
To help alert applicators and nearby growers of sensitive crops in the area, the University of Arkansas launched a color-coded flag system in 2011.
Even with the flags, Bob Scott, University of Arkansas Extension weed specialist based in Lonoke, says paying attention to wind speed and direction, boom height, nozzle and spray droplet size, sprayer speed and climatic conditions are key to reducing the risks of off-target herbicide movement onto a sensitive crop.
Of those factors, he says wind has the greatest influence on drift.
Last season, Scott visited several rice fields with suspected herbicide drift, but he says the overall number was more in line with what he considered normal. Scott blames bad years on prolonged periods of wind when growers or applicators get behind schedule and may push the envelope a bit too far.
Years when wet fields delay rice planting also can be problematic as growers hurry to get fields sprayed. And the amount of planted rice acres also can intensify the problem.
“It’s one of those things that kind of comes and goes,” Scott says. “We’ve had bad drift years and we’ve had good drift years. I think the Flag The Technology program has helped.”
And he suspects many cases of mild drift go unreported.
Bobby Golden, an agronomist at the Mississippi State University Delta Research and Extension Center in Stoneville, also categorized 2015 as a normal drift year.
Out of the roughly 20 rice fields visited, he said only two had significant damage caused by glyphosate drift.
A few years ago, Scott says he received several calls about Newpath drift onto non-Clearfield rice or glyphosate drift from applications to Roundup Ready crops. But he says Clearfield rice acres have declined, and more growers have moved to Liberty Link crops as glyphosate-resistant weed problems have increased.
During the past couple of years, Scott says he has seen more drift onto rice from burndown herbicides used on other field crops.
Golden says he’s seen similar trends in Mississippi, particularly because his state has fewer rice acres than Arkansas.
“We’re seeing more coming off of pre-emerge soybean herbicides or burndown soybean herbicides, depending on the planting window,” he says.
One of Golden’s concerns this season is wet fields caused by earlier flooding. Once the fields dry, growers may be in a hurry to get them prepared for planting and may not pay as close attention to drift prevention as they should.
“It depends on how we dry out,” he says. “When we get in a big hurry and we’re planting rice and soybeans close together and in a tight time frame, it could be a problem.”
Watch droplet size
Many of the burndown products, such as paraquat, are contact herbicides, so applicators want a fine droplet size to obtain better coverage. But small droplets also are more susceptible to wind transport and drift, so it becomes a balancing act, Scott says.
The amount of chemical that drifts onto susceptible plants and the growth stage of those plants play a big role in the ultimate damage.
“It’s pretty simple,” Scott says. “The more chemical you get on a susceptible plant, the worse the damage and the worse the effect will be on yield. And the timing of the drift is also something that very much contributes to the eventual damage.”
If glyphosate, for example, drifts onto rice in the vegetative stage, Scott says in many cases the rice will grow out of it. The plants may be stunted and maturity delayed, but growers will still harvest a crop.
But if herbicide drifts onto rice during the reproductive stage, it may cause blanking of seed heads and serious yield losses. In either scenario, Scott says it’s difficult to quantify yield losses until the grower harvests the field. If conditions are right, drift may not just be one incident but the accumulation of two to three nearby passes. During each pass, a small amount of herbicide moves onto the sensitive crop.
“We do a lot of research on this because we need to know what these chemicals can do to off-target crops in any given drift event,” he says. “It’s very hard to know what’s going to happen until you put the combine in the fields.”
To help growers manage rice injured by drift, MSU graduate student Ben Lawrence is looking at nitrogen regimes as part of his doctoral research.
“What type of injury can you expect if this type of herbicide gets on the rice and how do you manage it going forward?” Lawrence says of his research focus.
Flag The Technology
To help warn applicators and growers about neighboring sensitive crops, the University of Arkansas launched the color-coded Flag The Technology system in 2011.
The colors denote the crop’s herbicide-tolerant trait or lack of herbicide tolerance. Red, for example, denotes a conventional crop that is sensitive.
Bright yellow, on the other hand, signifies a Clearfield crop. As new herbicide traits come on the market, flag colors have been expanded. The latest addition is purple with the Provisia logo, which will mark rice fields tolerant to Provisia, or quizalofop herbicide, once the product receives Environmental Protection Agency registration.
The Arkansas Soybean Research and Promotion Board provided funding for direct purchase of flags during the 2013 and 2014 seasons, giving the program a big kick-start, Scott says.
Two years ago, a supplemental cloud-based field identification system was introduced, but it is still in development.
“What I’m seeing now is rather than flagging all of the fields, growers who are using this are flagging trouble areas,” he says. “If they have conventional rice near Clearfield rice, they’re using the technology on an as-needed basis and where it has a fit.”
The color coding has been adopted by both the Southern Weed Science Society and the Weed Science Society of America, Scott says.
Texas also has expressed interest in the flags, and he gave a presentation on the subject at the Texas Plant Protection Association’s annual conference in December 2015. Scott also has received inquiries from as far away as Canada and Brazil.
To learn more about the Flag The Technology system, visit University of Arkansas.