Over the past year, LSU AgCenter researchers have been fighting an uphill battle against stemborers in the most commonly grown rice variety in southwest Louisiana, PVL03. A widely used pesticide has suddenly begun to prove ineffective on the insect, and entomologist Blake Wilson is working to find out why.

Wilson says that for approximately the past 15 years, stemborers have been controlled by the seed treatment Dermacor X-100, which has also historically been used in curbing the rice water weevil.

“But this year we’ve seen reduced control of the rice water weevil and almost no control of stemborers,” Wilson said. “The Dermacor failed not just at the rice research station, but also in commercial fields around the state.”

Development of insecticide resistance is common in chemicals that have been widely used for years, but Wilson says the ineffectiveness doesn’t necessarily fit the pattern of pests building up resistance due to that fact that the control failures occurred with all the insect species at the same time.

“It’s not impossible that it’s resistance, but that would be highly unusual,” he said. “We just know it’s not working like it used to.”

On a positive note, Wilson and his colleagues began a project last year that looks at alternative management strategies for stemborer control, particularly host plant resistance, but also identifying better scouting scenarios for foliar insecticide application and determining what stage of the crop is most susceptible to the pest.

Wilson says that absent PVL03, he and his researchers have identified varieties that are showing stemborer resistance that might not require insecticide protection.

Other ongoing projects focus on:

Apple snails. In addition to continuing the use of copper sulfate to control apple snails, researchers have begun to attempt to manipulate crawfish production practices to make the environment less conducive to snail populations. One option may be switching from rice to sorghum sudangrass as a forage crop for crawfish to clean up the worst impacted fields that farmers can no longer crawfish in. This would be a potential solution to allow producers to continue to fish their ponds without having to fully dry them out in an attempt to eliminate the invasive species of snail.

Extension associate and master’s student Christine Gambino applies

insecticidal seed treatments to rice. Photo by Schyler Thibodaux

Row rice. Seed treatments for billbugs in row rice have continued to be ineffective, which has led to multiple applications of insecticide to keep the crop free of the pests. There has yet to be an economic analysis to judge if the cost of numerous applications outweighs the profit from potentially higher yields.

Insecticidal seed treatments. Last year treatments were up to 50% less effective in controlling the rice water weevil and stemborers in rice planted late in May. This year that figure held steady regardless of planting date. Multiple controls need to be integrated for rice water weevils to prevent substantial yield loss across the state. These include using seed treatment as well as spraying a foliar insecticide at the flooding stage.

Emerging pests. With the Mexican rice borer becoming more established in the state, researchers have begun carefully monitoring the rice delphacid, which has been reported consistently in Texas and has likely moved eastward.

AgCenter plant pathologist Felipe Dalla Lana has discovered an incident of a disease called hoja blanca, or white leaf rice virus, which is only known to be vectored by the rice delphacid, so it’s likely already here although AgCenter entomologists have yet to locate it.

Extension associate and master’s student Christine Gambino examines cover crops at the H. Rouse Caffey Rice Research Station. Photo by Blake Wilson