Rice Farming

Weed Wars

Troublesome weeds and what farmers
can do to combat them

By Carroll Smith

As the 2009 growing season kicks off, farmers across the country are gearing up to address the perennial threat of weeds in their rice fields. These pests come in all shapes and sizes, some tougher to control than others, but at least they are consistent in one way – they will show up. Thus, it’s up to the farmer, universities and industry to figure out the best options for controlling these troublesome weeds’ yield-robbing potential in rice.

University of Arkansas (U of A) Extension weed scientist Bob Scott reminds producers that propanil-, Facet- and Command-resistant barnyardgrass (several different biotypes) have already been confirmed in the state. A new twist in the resistance issue is that U of A’s Dr. Jason Norsworthy announced last year that he had discovered the presence of an ALS-resistant barnyardgrass.

“Since Newpath is an ALS herbicide, and 60 to 70 percent of our acres are going into Clearfield this year, we are encouraging growers to incorporate more than just Newpath into those herbicide programs,” Scott says. “In the Clearfield fields, we recommend using either Command or Facet up front or choosing a tankmix partner for Newpath that will control broadleaves and also help on barnyardgrass to prevent ALS resistance from developing. Don’t just go out with two shots of Newpath.”

In fact, no matter what varieties a farmer grows, Scott emphasizes that the general message regarding weed resistance this year is not to rely on just one herbicide for barnyardgrass control.

Consider the overall weed spectrum
On other weed fronts, the Arkansas weed scientist says that Regiment is “the best thing we’ve got to control smartweed, but since Regiment also is an ALS herbicide like Newpath and Grasp, it’s not particularly a good tankmix partner in terms of resistance management.

“However, if a farmer is using a Command-based program on conventional rice, then Regiment could be incorporated as another mode of action,” he says. “It depends on what kind of system you are in. We use Regiment for broadleaf control, especially on smartweed acres and on bigger barnyardgrass later in the season.”

Scott goes on to say that Strada herbicide – also an ALS chemistry and fairly inexpensive – is a good fit with the Clearfield rice system because it can be tankmixed with Newpath to pick up hemp sesbania and northern jointvetch.

“Once again, Strada doesn’t help on the herbicide-resistance front because it also is an ALS chemistry like Newpath, but it does fill the gap in the spectrum there,” he adds.

Questions about sprangletop and fall panicum
Further south in Louisiana, the top two most asked about weeds are sprangletop and fall panicum, according to LSU AgCenter weed scientist Eric Webster.

He attributes the resurgence of sprangletop to a couple of different factors. The first one is the loss of Arrosolo, which did a good job of controlling sprangletop, especially early in the season. The second factor is that farmers have not been including Bolero in their weed control programs as much as they used to. However, Webster notes that Bolero is being re-introduced to farmers’ weed control strategies through the herbicide Ricebeaux, which has the equivalent of three quarts of propanil and three pints of Bolero.

In regard to fall panicum, Webster says, “The reason we are having more problems with this weed is that we have moved away from our propanil-based program because our farmers aren’t basing their weed control decisions on barnyardgrass like they are in Arkansas.”

Strategies to take out aquatic weeds
Perhaps the biggest challenge currently facing Louisiana rice farmers, particularly those in a rice/crawfish rotation, are aquatic weeds, such as creeping burhead and bull tongue.

“If a farmer has to stay in a rice/crawfish rotation, I would recommend the Clearfield rice system, applying two shots of Newpath at the higher end of the rate range at six ounces each,” Webster says. “I also would consider including a pre-emergence herbicide like Command in the first Newpath application because Command is a good aquatic herbicide for those type weeds.”

Another option is to work the ground before planting instead of planting into a no-till or reduced-till system where these weeds have already emerged.

“I also would advise these farmers to drill seed and maybe bump up their seeding rate to get a good, thick stand of rice,” he adds. “Most of the time, those aquatic weeds don’t compete very well. That’s why I like to use Command in a system like this. It may not control the weeds for a whole season, but it allows the rice to get a competitive advantage.”

In addition to the various weed control strategies discussed in this article, an important point to remember is that every farming operation is unique in its own right, and each field should be evaluated on an individual basis to determine the weed spectrum that is present. Once that determination has been made, visit with your consultant, university personnel and industry reps to put together the best weed control strategy for your particular situation.

Contact Carroll Smith at (901) 767-4020 or csmith@onegrower.com.

Industry weighs in on weed wars out West

“Watergrass is the most competitive weed that California rice growers have to deal with, and that’s the first one they address immediately after planting,” says Rick Geddes, Dow AgroSciences.

Another very common and fairly widespread grassy weed throughout the western rice-growing region is sprangletop. In the sedge family, the two biggest problems are ricefield bulrush and smallflower umbrella sedge.

“We also have weeds that are collectively known as lilies–aquatic broadleaf weeds, such as ducksalad, California arrowhead and monochoria,” Geddes says. “The last weed that we address is redstem.”

Granite GR, which is manufactured by Dow AgroSciences, is a granular herbicide that can be used when rice reaches the 2 1/2-leaf stage.

“Granite GR is flown onto the water and does an outstanding job of controlling watergrass, is good at controlling California arrowhead, ducksalad and monochoria and will suppress redstem and ricefield bulrush,” Geddes notes.

Another formulation of Granite is Granite SC, which is a post-emergence foliar herbicide that is generally applied 30 to 45 days after planting to control watergrass escapes as well as the other weeds mentioned above. Granite SC also can be tankmixed with propanil, which helps control watergrass, and Grandstand, which is effective on redstem, he adds.

“All three herbicides are often mixed together,” Geddes says.

Get with the program
“There’s a lot of talk out here about a program approach to herbicides,” says J.R. Gallagher with Valent U.S.A. Corp. “If you use a grass product, you should also put out a broadleaf product.”

The concept behind the program approach is to get control of these weeds early, especially watergrass, to maximize rice yield potential. Also, using a combination grass and broadleaf product, such as Bolero UltraMax, will take out smallflower umbrellaplant and decrease the pressure on post-emerge herbicides, such as propanil, later in the season, he adds.

“Bolero UltraMax is a granular formulation that is flown into the floodwater,” Gallagher says. “We also tankmix Abolish, our liquid thiobencarb formulation, with Regiment CA and apply this combination at the four-leaf stage of water-seeded rice and the two- to three-leaf stage of drill-seeded rice.

“Typically, in a drill-seeded situation, Regiment CA is being used as a clean up spray for watergrass or barnyardgrass that came through the pendimethalin herbicide,” he explains. “In water-seeded rice, a lot of Regiment CA is being used in a program approach to control resistant watergrass. Growers apply Regiment CA 25 to 30 days after seeding, then a week later they will spray propanil over the top of that.”