Refuge requirements working in Bt cotton

Producers in the Upper Southeast look at refuge requirements for Bt cotton similar to growing conventional varieties of cotton, says a crop consultant. The bottom line with Bt cotton figures fewer sprays, but there's also the beginning of a trend toward insects they've not faced in large numbers before.

“The value of Bt cotton is definitely being proven here,” says Stan Winslow, president of Tidewater Agronomics, a crop consulting company. Winslow's company advises producers in northeastern North Carolina, as well as into Virginia.

The growers Winslow is working with haven't gone whole-hog with Bt. Their acreage is about half Bt and half conventional varieties, he points out.

That may account for how growers are looking at production these days, and refuge requirements, Winslow says. Growers this season made their refuge requirements based on the 95:5 option, the 80:20 option and the 95:5 option.

“They're not thinking of the refuge requirement as a refuge,” he says. “They're actually thinking of it as part of the crop.” The majority of the farmer-clients Winslow has worked with chose the 80:20 option, which lets them spray the entire field, both Bt and non-Bt varieties. One producer this season chose to use the imbedded refuge option, while another treated the crop on an as-needed basis.

“The refuge requirements have worked out very good,” Winslow says. “By having Bt in the mix, it has greatly reduced the number of sprays. If not for the Bt, they would have had to spray two to four times in the field for plant bugs.”

The refuge requirements have also pointed out problems. For example, tobacco budworms are showing some resistance to pyrethroids, Winslow says.

“We're also having a really bad problem with lygus bugs or plant bugs,” Winslow says. “Plant bugs are a lot more prevalent under a reduced-spray program, especially during August.” He's seen an increase in the problem over the last three years. “There's still a lot to be learned about how to manage insects in this system.”

Plant bugs feed early in the season on squares and cause fruit shed. As the bolls get established, plant bugs, as well as stink bugs, feed on them. Later in the season, lygus bugs feed on soft bolls and penetrate the seed and cause hard lock. “It's a consistent problem,” Winslow says.

Growers of Bt cotton had three options to choose from this growing season.

The first option, known as the 95:5 external structured un-sprayed refuge, means that at least five acres of non-Bollgard cotton — at least 150 feet wide — is planted for every 95 acres of Bt cotton. Insecticides labeled for the control of tobacco budworm, cotton bollworm or pink bollworm are prohibited. The refuge has to be within a half mile from the edge of the Bollgard field.

The second option, known as 80:20 external sprayed refuge, calls for at least 20 acres of non-Bollgard cotton for every 100 acres of Bt cotton. All of the cotton can be sprayed with insecticides labeled for tobacco budworm, cotton bollworm or pink worm. Under this scenario, growers cannot spray foliar Bt products.

The third option, known as the 95:5 embedded refuge, is similar to the first option in that it requires the farmer to plant at least five acres of non-Bollgard cotton for every 95 acres of Bollgard cotton. Under this scenario, the refuge must be imbedded as a contiguous block within the Bollgard field. In larger fields, multiple blocks across the field may be used. In small or irregularly shaped fields, neighboring fields farmed by the same grower can be grouped into blocks to make up a larger field unit. This unit must be within one mile squared of the Bollgard cotton and be at least 150 feet wide. The refuge can be treated with any insecticide, except foliar Bt products, labeled for tobacco budworm, cotton bollworm or pink bollworm whenever the entire field is treated. The refuge cannot be treated independently of the Bollgard field.

A fourth program is a community refuge program where growers combine their efforts to meet the refuge requirements.

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