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Corn+Soybean Digest

Bt Cotton: Is It For You?

Bt cotton has been good for Joe Morgan and his southern Mississippi farm. But he isn't sure if the newest round of Bt — Bollgard II — will be cost effective.

That's a question facing many growers who battle bad bugs every year. Will insect pressure be enough to merit an additional $7-8/acre technology fee they will likely pay for the kicked-up insect control?

Morgan farms cotton and peanuts near Hattiesburg, MS. Cotton bollworms and fall armyworms can be a problem. Bollworms are mostly controlled by varieties containing the Bollgard gene from Monsanto. The Bt varieties are stacked with Roundup Ready genes.

But if bollworm or armyworm pressure is too severe, he sometimes sprays once or twice with Karate from Syngenta. For control of stink bugs, he sprays Bidrin from AmVac.

“We've been growing cotton in rotation with peanuts since 1994,” says Morgan. “Bt cotton has worked well. We just aren't sure if we needed to spend the extra money for Bollgard II.”

His crop consultant, Trey Bullock, says Bt cotton has been insurance that budworms can't destroy the area's cotton production.

“I haven't seen a yield decrease or anything like that with it,” he says. “Bt cotton has been good. Bollgard II can help us more with fall armyworms, but we don't have to spray for those year-in and year-out. Right now we're spending about $5 for extra bollworm and armyworm control. So it's hard to tell if the product is a value for this area or not.”

Bollgard II is the second generation of insect-protected cotton developed by Monsanto. Its technology contains two different insect-control genes, compared to the single insect-control gene of its predecessor.

Monsanto received clearance to release the new technology last year, but seed availability was limited.

Bollgard II is supposed to control target pests including cotton bollworm, tobacco budworm, pink bollworm, European corn borer, cabbage and soybean loopers, fall and beet armyworms, saltmarsh caterpillar and cotton leaf perforators.

Mississippi State University entomologist Blake Layton has studied Bollgard II for about four years in both Delta and hill growing areas. He sees major benefits planting the new Bt if insect infestations are high.

“In terms of caterpillar control, Bollgard II is as much better than Bollgard as Bollgard is compared to conventional cotton,” says Layton. “In the few fields that were planted with the new Bt, there haven't been enough caterpillar (bollworm) infestations to require a spraying. It's as close to being worm-proof as we've seen, but we still see a few worms surviving Bollgard II. I expect there will still be times when Bollgard II fields have to be sprayed.”

The cost of Bt cotton will vary Beltwide. In the Delta area, Bollgard's cost is about $32/acre. For Bollgard II, expect to pay an additional $6-8, says Layton.

In areas where bollworm or fall armyworm pressure is consistently heavy on Bt cotton, there is a cost benefit to using Bollgard II. However, some Southern areas tend to benefit more from Bollgard. In 2002 Bollgard cotton had to be sprayed for caterpillar pests an average of 1.17 times in 66 MSU test fields. That compared to 3.35 sprays for non-Bt fields.

In the Delta, the average Bt field required two sprayings, compared to 5.3 for non-Bt fields. In the Mississippi hill area, the average Bt field needed only 0.65 sprayings, compared to 2.1 on non-Bt.

“However, we've also seen that, because of the reduced number of sprays for caterpillar pests, Bollgard cotton requires additional sprays for bug pests,” says Layton. “This is especially true in the Delta region of Mississippi where plant bugs are a more consistent problem. Thus, part of the additional reduction in caterpillar sprays that will be provided by Bollgard II will likely be offset by an increase in bug sprays.”

Steve Micinski, Louisiana State University research entomologist at the Red River Research Station, Bossier City, says Bollgard II has several advantages over Bollgard.

“First, the addition of the new ‘Cry2Ab’ gene may reduce the likelihood of insect resistance in the insects the original Bollgard controlled,” he says. “Second, some increased spectrum of insecticidal activity has been observed.

“Soybean loopers, which were at best only suppressed by Bollgard cotton, appear to be controlled by Bollgard II,” Micinski adds. “Bollworm/tobacco budworm damage is less in the Bollgard II test plots than the Bollgard plots, although differences were small.”

He calls Bollgard II “a significant jump over Bollgard,” particularly in bollworm control.

“It's still early to tell if additional spraying will be needed over a large area. But on small test plots, it doesn't look like any spray applications are needed,” he says, noting that northern Louisiana insect pressure was only moderate in 2003.

Layton says that even though Bollgard II cotton may require no spraying, growers are still encouraged to scout their fields. They may still face insect pressure from plant bugs that can plague the Delta region.

“They may have to spray for plant bugs, which could mean close to a wash on the overall cost,” he says. “But the real advantage will be the security the new Bt will provide against so many other insects, including armyworms and loopers.”

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