For nearly a decade, LSU AgCenter entomologist Blake Wilson has been facing an uphill battle over stem borer and rice weevil infestation in rice crops, particularly the most popular variety in the state, PVL03. For the last three years, a formerly effective insecticide has become decidedly less so in controlling the pest.

Dermacor X-100 had been the go-to insecticidal seed treatment used to control both stem borers and the rice water weevil. Wilson said that technology has been worth millions of dollars to the Louisiana rice industry, but since 2022 things have changed.

“The seed treatments in the past three years have begun to lose efficacy, providing about 50% control of the rice water weevil and almost zero control of stem borers,” he said. “So that’s forced us to go back to the drawing board on researching management strategies.”

Wilson said this year his team has conducted more stem borer experiments to identify alternative management strategies, especially in late-planted crops where things have gotten particularly bad.

“We have a lot of later-planted rice in South Louisiana due to crawfish farming so some of these fields can get hit harder,” he said.

One potential solution is the insecticide Vantacor, which has essentially the same chemical makeup as Dermacor, but it is applied as a foliar product during the growing season as opposed to the seed stage. This led to many questions from growers about exactly when to apply it and how you scout for stem borers.

Wilson said with seed treatments, the decisions are made before the rice is planted, but now growers and consultants must watch more closely, identify fields that will benefit from being treated and know when to apply it. The seed treatments remain beneficial in rice water weevil management.

One of Wilson’s doctoral students has conducted both greenhouse and field experiments to get to the bottom of things, determining that the insecticide provides the best control when applied to rice at the 1-inch panicle growth stage.

Wilson says there will always be some loss of yield due to pests, but he and his team want to reduce that as much as they can and keep infestations at acceptable levels, which he would estimate at five weevil larvae per core.

“Even 50% control is not something you want to throw away,” he said.

Other ongoing projects focus on:

Emerging pests. The rice delphacid, which has been damaging fields in Texas, has migrated to Louisiana, Mississippi and southern Arkansas. Wilson said that a task force among universities is monitoring the threat and evaluating potential controls.

Apple snails. This year, Wilson’s team is looking at sorghum and sudangrass to provide forage for crawfish instead of rice 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.