Weed resistance is no longer something that might happen someday in southern rice fields. “It's real,” says Ken Smith, University of Arkansas weed specialist.
“I'm not sure what we're doing wrong — but we're adding another weed to the herbicide-resistant list every two years since 1995. All of these aren't in rice, but rice has its share.”
Smith and other rice specialists from across the U.S. rice belt recently shared views on weed management and other production issues, including disease and insect management, at the annual Valent-sponsored Rice Seminar in San Antonio.
Weed resistance is an issue that concerns growers in every rice-growing state.
Barnyardgrass, for one, is becoming “resistant to herbicides we use in rice as well as in cotton,” says Smith. “We've been fortunate for the last few years to have new compounds available in rice, but we're about at the end of products with new modes of action.”
In Texas, specialists said, continuous rice creates concern about herbicide-resistant weeds; red rice resistance is of particular concern.
“We've had a hard time finding a consistent program,” says Eric Webster, Louisiana State University. “But we've sprayed a lot of Facet, and we haven't seen resistance. Our growers are good about rotating chemistry, so we don't have a consistent pattern of herbicide use.”
Specialists say Clearfield rice has performed well, but resistance is an issue they all watch. They are concerned about potential for outcrossing of red rice.
With some 30 percent of Arkansas acreage planted to Clearfield varieties in recent years, Smith says red rice resistance claims a top spot on his watch list. “Resistance will come to all of us — and not just in Clearfield varieties, but others, and not just from red rice, but also in other weeds such as barnyardgrass.”
Jason Bond, Mississippi State University, says herbicides don't seem to be as effective on sesbania.
“One of the problems we face is a lack of new herbicides,” says Tim Walker, research professor at Mississippi State University. “Not many new pesticides are being developed. We wonder if it's possible to evaluate pesticides labeled in other countries and push to bring those into the United States. Are there products with potential for U.S. labels?”
Grower organizations also are concerned about a slowdown in pesticide development, he says.
Valent representatives said if products labeled in other countries are useful in rice production, companies are trying to get them approved for U.S. use.
Seminar participants also discussed disease problems. Don Groth, Louisiana State University, says narrow brown leafspot (Cercospora) infection caused considerable yield loss in some Louisiana fields last year. “It's not usually a significant problem,” he says.
It is slow to develop, requiring from 30 to 35 days from infection to symptoms. “The plant is susceptible at all growth stages. We have identified numerous races, based on reactions of several cultivars.”
Groth says symptoms in the 2006 crop were a bit different than usual. “Lesions were broader and longer and more numerous.” Some growers suspected blast infection.
CL 131 appeared to be the most susceptible variety, but Cl 151, Cocodrie, and Cheniere were also infected. “That represents a significant percentage of our acreage,” he says. “The disease began to manifest late in the season and then tended to desiccate plants. Photosynthesis stopped.”
Samples revealed several diseases in the field, but Cercospora accounted for 70 percent — “levels we've never seen before.”
Fungicide trials indicated Tilt as the best control option, and yield response ranged from 600 pounds to 700 pounds per acre with Tilt treatments. Milling values also improved. Tilt response was best when applied at heading.
The reason for the increased infection rate and crop injury is a mystery, Groth says; he speculates that the warm winter may have been a factor. “We also were wet during July, and that favored disease development. We could be seeing a race changes as well. The best looking fields were the hardest hit.
“Could it happen again? We don't know, but experience says no. We have a major source of the inoculum, but a good freeze should have killed it.
“We still have questions. We have only one year's data, no proven scouting method, and no treatment threshold. It has been a minor disease for so long that we have little research on it.”
He says the disease can develop late in the main crop and then hit a ratoon crop hard.
“We saw it in Texas about four years ago,” says Texas Extension Specialist Garry McCauley. “It came in on the main crop and devastated the ratoon crop.”
Specialists say fungicide use could shift because of Cercospora outbreaks. Many will add Tilt to the schedule.
Effective insect control also poses problems for rice growers. Stinkbugs, for instance, have required as many as six pesticide applications in Texas.
“We average three treatments per year,” said Texas Extension Entomologist M.O. Way, “but some fields needed six.”
Texas applied for a Section 18 exemption from EPA last year for Orthene to help control stinkbugs. “Pyrethroids work well,” May says, “but provide little residual activity. Orthene would help but the request was denied. They encouraged us to re-submit, and we'll try again this year.”
The problem is that approval includes a target loss of 20 percent of crop value, and Way says yield losses aren't that significant — but quality reductions could be.
“It's hard to quantify quality losses to EPA. We hope to strengthen the application package for 2008.” Way says EPA has also shown a reluctance to approve new uses for organophosphate insecticides, “But our farmers need something to control stinkbugs.”
He also reported on a potential new scouting technique for insect infestations. The sweep net has been the industry standard, but Way says that process is time-consuming. “It's tough duty in July, when it's hot and humid, and we need a better sampling technique.”
He says a graduate student, Luis Espino, is working with a sweep stick, a three-foot long section of PVC pipe. A scout makes a 180-degree sweep and counts the number of adult stinkbugs disturbed by the last 15 inches of the sweep stick.”
“Two passes with a sweep stick equal 10 passes with a sweep net,” Way says. He hopes simplifying and standardizing scouting techniques will get more farmers in the field sampling for stinkbugs.
In most years, Texas treats every rice acre for stinkbugs, he says, and from 50 percent to 60 percent of acres get treatments for rice water weevils, chinchbugs, stem borers, and other pests.
Chuck Wilson, University of Arkansas rice specialist, said farmers in his state treat from 35 percent to 40 percent of their acreage for water weevils each year. “For stinkbugs, it depends on the year — 75 percent to 80 percent some years, and 25 percent some years. It's cyclical.”
Mississippi farmers spray 30 percent to 40 percent of acres for stinkbugs and 50 percent or more for water weevils, says Mississippi State University Specialist Nathan Buehring.
California has no problem with stinkbugs, but 25 percent of the rice acreage is treated for water weevils and 5 percent to 10 percent for armyworms, specialists say.
California Rice Farming System Adviser Larry Godfrey said pyrethroids provide the greatest effect on weevils, but those materials “are under scrutiny in California. We need new products for water weevil control. Pre-flood materials are our first choice, and seed treatments also show a lot of potential.
“We're also looking at other insect issues, such as West Nile virus. We're developing pest management techniques to manage mosquitoes in rice fields.”
Stem borers are also appearing on entomologists' radar screens.
“We've seen pretty severe infestations in southeast Arkansas,” Wilson says. “A 180-bushel yield potential may drop to 40 bushels. Corn in rotation could be a factor and increased corn acreage this year may spread the pest to other areas.”
“It's an increasing problem in Texas,” Way says. “Just five or six years ago, no one was treating — now it's common to treat for stem borers.”
He says three different stem borers affect rice in Texas: the sugarcane borer, the Mexican rice borer, and the rice stalk borer.
“The sugarcane borer and the Mexican rice borer are the most prevalent. Farmers need to scout to determine if treatment is needed. Inspect rice culms for stem borer lesions early and late in the season.”
Wilson says chinchbug infestations in Arkansas last year were the worst he'd seen in years. “They were bad in Texas, too,” Way says.
Valent is a long-time sponsor of the Rice Seminar as a service to growers and the industry, says Greg Rich, product development manager.
“Each year at key professional meetings, university research and Extension personnel have a chance to see each other, but often there is precious little time to interact and discuss how their work may be used by growers.
“This seminar lets rice researchers and Extension personnel from all rice-growing states come together to discuss topics of mutual interest and share data, ideas, theories, problems, and solutions. Participants use what they have learned to help rice growers in their respective areas in the coming season.
“It's a great collaborative effort, and Valent is proud to be part of it. We've sponsored the Rice Seminar for more than 20 years and will continue to offer this service to the industry.”