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Mexican rice borer threat

Gene Reagan, LSU AgCenter entomologist, has been doggedly studying the Mexican rice borer’s spread northward from the Rio Grande Valley for almost 30 years.

The insect, which damages rice and sugarcane, has been migrating through Texas at the rate of 15 miles a year. In 2006, it was found in east Texas just one county away from Louisiana, and, sure enough, two weeks before the end of 2008, borers showed up in two traps on the Louisiana-Texas line north of Vinton.

The traps have been maintained and checked by personnel from the Louisiana Department of Agriculture and Forestry since 2001.

“It’s still about 15 to 20 miles from any sugarcane fields in Louisiana,” Reagan said.

A quarantine preventing Texas cane from entering Louisiana remains in effect as a means of slowing the borer’s spread. But the spread is likely to continue, and that has Reagan worried. “I think we’ve got some major problems down the road.”

Reagan first saw what the pest can do in 1980. He traveled to the Rio Grande Valley in Texas and was astonished at the damage to sugarcane. “I saw many fields that were totally destroyed.”

Texas cane producers have learned to cope with the problem by developing resistant varieties and by using irrigation to lessen drought stress. The insect is inclined to lay its eggs on dying leaves on the lower part of the sugarcane plant and prefers drought-stressed cane plants.

“I anticipate the Mexican Rice borer will be more of a problem in sugarcane than in rice,” Reagan said.

An economics study conducted last year by the LSU AgCenter and Texas A&M projected a $45 million loss of revenue for Louisiana rice farmers once the entire state is infested. Mexican rice borers are not obvious pests in rice until the crop is in the boot stage. By the time it is found within rice plants the population jumps rapidly.

Between growing seasons, the insect is found in high numbers in grasses such as Johnsongrass. “It was phenomenal to me the numbers we found in weeds in the Texas rice-growing region,” said Reagan.

Once the insect bores into sugarcane, insecticides don’t work well because the cavity created by the borer is filled with chewed plant material, frass, blocking a chemical’s entry.

Insecticides work better on the pest in rice although three applications may be required. A new seed treatment, Dermacor, appears to control the pest in rice. Originally, Dermacor was developed as a seed treatment for drill-seeded rice against the rice water weevil.

Reagan said Dermacor also has potential to protect sugarcane and hopes to persuade the chemical’s maker, DuPont, to pursue labeling for that crop.

Reagan has worked to develop a response to the insect before it becomes a pest in Louisiana. “I’m a champion of proactive research.”

A natural enemy of the borer, a wasp found in the Rio Grande Valley, will be tested in Louisiana by the U.S. Department of Agriculture.

Reagan’s work on the Mexican rice borer has been funded with $1.5 million in competitive grants involving joint efforts with entomologist M.O. Way of Texas A&M University. For several years, Reagan and Way have held a field day near Ganado, Texas, to show how the pest has affected rice and cane in the Lone Star State.

“It’s been a good collaboration,” Reagan said. Without the TAMU cooperation “we clearly would not have gotten any of those grants.”

Reagan said it’s unlikely the grants would have been approved for the project if its scope were limited to sugarcane. But adding rice to the grant application made a significant difference. “It’s also much more practical because the insect feeds on both crops.”

Way said Reagan approached him about 10 years ago with the prospect of a cooperative research venture. “We appreciate the cooperation from the LSU AgCenter. The funding has allowed us to expand our program to do long-term research.”

The Mexican rice borer became a pest in Texas rice in 1988. Yield losses in rice can be as much as 500 to 1,000 pounds per acre.

Way said rice producers in Mississippi, Missouri and Arkansas are watching results of the research. So far, studies have shown the pest is more of a problem in late-planted rice. Some rice-growing regions in Texas are more likely to have problems with the insect. It has been severe south of Houston, but it is becoming a more serious pest in the Beaumont area.

Research is under way to determine a threshold for spraying pyrethroids, Way said. The threshold would rely on the number of lesions found on plant stems.

Texas rice farmers have found that pyrethroids for the borers can be tank-mixed with fungicides sprayed at late boot and early heading stages. That strategy was developed with help from Don Groth, LSU AgCenter plant pathologist, at the LSU AgCenter’s Rice Research Station in Crowley, La.

TAGS: Rice
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