When technology reaches a certain effectiveness and ease-of-use level, it’s easy to become somewhat complacent, even if it’s not intentional. In agriculture, if a product is working well, most farmers will continue to keep it in their production system. However, in the case of weed control, the wake-up call comes in the form of weed resistance. No matter how many times you apply products that have been very effective in the past, these troublesome weeds just refuse to lay down and die.
In the last couple of years, weed resistance has been the hot topic for many crops, and rice is no exception. In the war on weeds, the entire industry refuses to surrender its fields to these pests, and, instead, has concentrated on actively developing effective strategies to keep even resistant weeds in check.
Brad Koen, who is a crop consultant in the Grand Prairie region of Arkansas, says crop rotation is prevalent in his area where farmers plant soybeans for two years followed by a year of rice. Lately, he says, their biggest struggle in rice has been with broadleaves, such as ground cherry, morningglories, hemp sesbania and indigo.
“We’re starting to see pigweed on the levees, too, where the seed banks have built up,” Koen says. “This weed problem we’re experiencing stems from planting Roundup Ready soybeans for so many years. Broadleaves are a gap in the Roundup weed control system. We’re also having a harder time controlling barnyardgrass and sprangletop. We used to use Facet preplant, but would miss the sprangletop. Then we went to Command preplant, but the residual is not lasting as long or the sprangletop is beginning to develop resistance.”
Koen says they are now using a new strategy by splitting the Command application – part of it goes out early and the remainder prior to flooding.
“We’ve also started using Facet and propanil pre-flood,” he adds. “Facet helps out with grass control, but it also has a lot of broadleaf control for us. We’ve used quite a bit of Broadhead herbicide (a pre-mix of quinclorac and carsentrazone-ethyl), which picks up broadleaves and gives us some grass residual control. If we can get enough residual control, we may be able to avoid having to apply anything at mid-season and save a trip across the field.”
Bob Johnson, FMC’s Retail Market Manager, emphasizes the flexibility and effectiveness of Broadhead.
“The application is flexible because the herbicide can go out on two-leaf to five-leaf rice, depending on the weed spectrum a producer is targeting,” Johnson says. “The effectiveness of Broadhead refers to its control of numerous tough grass and broadleaf weed species available in one package.”
Continuous Rice Weed Spectrum
Jim Whitaker, of Dermott, Ark., who farms with his brother Sam in a continuous rice, zero-grade system, notes that their weed spectrum is a little different from that of a rice/soybean rotation.
“We are starting to see some ALS resistance in annual sedge, and more sprangletop is getting by Command,” he says. “We are beginning to go back to some of the old chemistry like Bolero.”
With invaluable input from their consultant Robb Dedman, ProAg Consulting, Whitaker says they have come up with some successful weed control strategies. On the Clearfield acres, they usually start out with a residual, which is Clearpath (Facet and Newpath) combined with either Prowl or Command.
“When we come back with our second shot of Newpath, we lay down another residual, which is either Newpath and Rice Beaux or Newpath and Bolero,” he says. “This is usually what it takes to keep the crop clean and pick up all the broadleaves. The reason for our approach of laying down two layers of residuals is that we don’t want to ever see any weeds. We don’t want them to get established.
“One of the broadest spectrum herbicide programs we’ve used is the Newpath and Rice Beaux tankmix,” Whitaker says. “With that second application, very few weeds get by this combination.”
Louisiana’s Weed Issues
In Louisiana, weed scientist Eric Webster says farmers around the Bunkie area also are having problems with sprangletop resistance, especially where multiple applications of Clincher have been made without adding anything else to the system. A bigger problem that Webster sees on the horizon is aquatic weed infestations. This past year, many farmers were paid to hold water in their fields to create wildlife habitat after the oil spill in the Gulf of Mexico took place.
“A lot of fields that will be planted to rice this year have been under water and have not been allowed to dry out,” he says. “This is going to increase the presence of aquatic weeds, which are tough to control. One program that could be of help is applying Command early followed by Grasp as a late-post treatment.”
Another issue that Webster has observed, particularly in south Louisiana, is occurring where hybrids have been planted behind hybrids for several years without rotating.
“I’ve seen fields where a Clearfield hybrid was planted, then it comes back on its own the next year basically as a weed,” he says. “About 25 percent of the plant population that comes back is resistant to Newpath. If it’s resistant, you can’t clean it up. We are currently involved in a rotation study to find ways to get these areas cleaned up.”
Herbicide offers contact and residual control
Barnyardgrass Under Scrutiny In Mississippi
In looking to the 2011 growing season, Jason Bond, Mississippi State University weed scientist, says he sees a couple of potential weed challenges on the horizon, but hasn’t confirmed anything to date.
“We had some problems last year with barnyardgrass showing up in Clearfield rice,” Bond says. “We have two suspicious fields where barnyardgrass may have developed resistance to Newpath. We’re trying to increase the seed so we can do a full study. We’re keeping a close eye on this, especially after Newpath-resistant barnyardgrass was confirmed in Arkansas last year. We’re expecting an increased problem with this scenario in Mississippi in 2011.
“The fallback treatment is Command,” he adds. “Farmers need to have a clean field at planting and then utilize residual herbicides so that the barnyardgrass doesn’t get out of control. Also, farmers need to tankmix another product with Newpath to control barnyardgrass in those areas where Newpath is not working as well. The treatments we’ve found to be effective in the past have been several different formulations of propanil and propanil pre-mixes. The challenge here is if the barnyardgrass is resistant to propanil as well.”
In this case, farmers need to rely on residual herbicides, such as Command, Prowl, Facet or Bolero, Bond says.
“I think the best time for Command to go out is at planting after controlling any barnyardgrass that has already emerged,” he says. “A lot of producers use Roundup plus Command at planting. Roundup controls any grass that has emerged at the time that you plant, then, hopefully, Command will provide residual control on grass that has not yet emerged.
“In our plots at the station, we use Rice Beaux, which is a pre-mix of Bolero and propanil, because we don’t have any propanil-resistant barnyardgrass here,” Bond continues. “It’s the same concept as Roundup and Command, and Bolero has post-emergence activity on barnyardgrass, too. In other words, propanil will control grass that emerges following the Command application, and Bolero will provide additional residual.”
Rice Flatsedge Populations Increasing
In the past, rice flatsedge has been considered a secondary weed, Bond says. However, last year, he observed some fields with dense populations of this pest. The suspicion is that the weed may be showing resistance to Permit. He has also observed flatsedge coming through two ounces of Permit in the field and in the greenhouse.
“Normally, flatsedge is fairly easy to control,” Bond says. “For instance, if we apply Rice Beaux early in the season for barnyardgrass, it should take care of rice flatsedge as well. Propanil does a good job on it, and Bolero provides extra control.
“In the past, we haven’t had a problem with this weed because when we applied Permit to control yellow nutsedge, Permit also picked up the flatsedge,” he explains. “But when Permit fails to work, we begin to notice flatsedge, which we didn’t scout for before. Where we’ve seen dense populations, we’re not sure what the yield impact was, but it definitely affected the growth of the rice.”
As Bond notes, the heart of today’s weed control battle plan is to use multiple modes of action multiple times.
Contact Carroll Smith at firstname.lastname@example.org, (901) 767-4020.