Those wanting to combat rice water weevils using Dermacor must use the product properly. This year, the product was labeled for Louisiana and other Southern states under a Section 18. Application is restricted to dry seedbeds — either drilled or dry-broadcast rice.
“Treatments must be made by certified treaters and there are a number of them in Louisiana,” said Natalie Hummel, assistant professor with the LSU AgCenter entomology department. “The reason DuPont took that approach is to ensure the quality of the product, that it went onto the seed at the proper rate.”
Producers must properly estimate the seeding rate to be used.
“It’s very important that estimate be on the mark because if you end up putting out less seed, the product won’t go out at the proper rate,” Hummel told the crowd at the recent Rice Research Station field day in Crowley, La.
Hummel is aware of at least one commercial plot where the seeding rate was incorrect. “The prediction was for a 50-pound seeding rate. The drill didn’t work properly and the seeding rate was only 35 pounds. It appears that might have affected the efficacy of the product.”
Overall, Hummel and colleagues are studying commercial fields in eight parishes across the state. “We want to know how the product works on a commercial scale. The reduction of larval populations on root masses was anywhere from no difference with the check to a 12-fold decrease in larval populations. On average, the reduction was about a six-fold decrease. I still have datasets coming in that I’m summarizing.”
In most of Hummel’s studies, “Dermacor activity has looked better than the pyrethroids. But the pyrethroids are still working well when used the right way.
“Keep in mind, the pyrethroids are adulticides while Dermacor is a larvicide. Dermacor is the only product currently on the market with larvicidal activity. It works by being taken up into the plant material — both above the soil line and into the roots. It kills the larvae when they feed on the roots.”
Two of the pyrethroid checks looked “very good. But in one case, because of the weather, the pyrethroid wasn’t applied until 11 days after flood. In that case, you couldn’t tell any treatment had been made. This is a good illustration that if pyrethroids can’t be applied at the right time, it may not be worth putting the treatments out. You can’t miss the window to control the adults. The pyrethroids form a film on the water surface.”
Once the larvae are at the plant roots, there will be no control by pyrethroids.
“There has been a myth floating around that Trebon has the ability to control larvae on roots. I’d like to drive home the message that, as far as we know, it doesn’t have that ability.”
Hummel has also been studying invasive pests in Louisiana rice. “The first is the South American rice miner, which is a sporadic pest in the state. It’s been here for several years, now.”
The second is the Mexican rice borer. “The pest hasn’t been reported in Louisiana yet, thankfully. But it is very close — one county from the (Texas) border, I believe.”
The third pest is the channeled apple snail, which can grow to the size of a baseball. “This is a new pest we’re watching for. It’s a large, aquatic snail that will feed on rice under the surface of the water.
“When you see the size of the shell, you think, ‘how could anyone miss that?’ But since it’s underwater, it can go unobserved.”
Anyone who discovers the snail after draining fields, “please let us know. So far, it’s been found in a Houma bayou area. But it hasn’t been found in rice, yet.”
The snail is an important pest in Asia. It has also been found in Texas rice fields, but hasn’t yet caused substantial losses.
Last year, another invasive pest, the panicle rice mite, was discovered in Louisiana, Texas and Arkansas.
“I understand state and federal agencies will get together on some conference calls in the next couple of weeks to discuss changing the regulatory situation” regarding the mite. Hummel says a survey of states hit with the pest is expected to begin shortly.
One survey was done last year in a Vermilion Parish commercial production field. “We continued that through the winter. After the rice was done and degraded, we checked all the different grasses. The mites dropped to an undetectable level for multiple samplings. They either went away, died off or have a resting form we’re not aware of.”