Rice water weevils infest almost every acre of rice in Mississippi to some extent, says Jeff Gore, assistant research professor, Delta Research and Extension Center.

Just one weevil per core can reduce yield by as much as 1 bushel per acre, he told producers attending the Delta Ag Expo.

Planting date can affect density of the pest, he says, “but it varies from year to year and there’s no way to predict it.”

Managing the pest with foliar-applied insecticides can be “highly variable,” Gore notes, but seed treatments do a good job of reducing weevil numbers and are more consistent.

Two new seed treatments, granted full labels in 2010 — Dermacor X-100 from DuPont and CruiserMaxx from Syngenta — do a good job of reducing the number of weevils, he says.

In three-year studies at the research center and on grower farms, percentage of control has varied widely, depending on initial larval densities.

In general, Gore notes, little benefit is obtained with either material if rice water weevil densities are low (1 to 2 weevils per core). Benefit increases as the insect density increases.

Both seed treatments produced “significant benefits” in terms of yield, he says. Over the three years of the studies, Dermacor X-100 provided an 11.8 bushel increase, with a 72 percent probability of a net return over costs, and CruiserMaxx gave an 8.3 bushel increase, with a 79 percent probability of a net return over costs.

A product expected to be available in the near future, Nipsit Inside from Valent, will offer growers another product for rice water weevil control, Gore says.

In 2009-10 studies, Nipsit did not provide a benefit when insect densities were low, but at moderate to high densities, it gave control similar to CruiserMaxx, with an average yield benefit of 9 bushels per acre.

Since the product price is not known, no economic benefit analysis could be done, but Gore says the probability of a net economic return will likely be similar to CruiserMaxx and Dermacor X-100.

Last year was “one of the worst in a long time” for fall armyworms in rice, Gore says. “We had a lot of calls from growers about lack of control with pyrethroids in later rice. Because there’s a lot more plant mass late season, it’s a good idea to bump up the rate of the pyrethroid for better control.”