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Secondary pests can cause primary headaches

The boll weevil is quickly becoming a pest of the past in many locations in the Mid-South, and Bt cotton is eliminating or reducing several species of caterpillar insects from cotton fields.

With traditional sprays for these pests on the decline, it's not surprising that other pests are now filling the void.

And while these critters do not have the crop damaging potential of their predecessors, they shouldn't be underestimated either.

One of these pests, the plant bug, is not quite the problem in the upper Mid-South as it is in the heart of the Delta.

Nonetheless, in 2002, it was the fourth most damaging pest in Tennessee and incurred the second highest cost of control for the region at a little over $10 per acre.

The pest presents a special challenge for cotton producers in the upper Mid-South, Extension cotton entomologists say.

According to Scott Stewart, cotton insect specialist at University of Tennessee's West Tennessee Experiment Station in Jackson, Tenn., plant bugs are tough, mobile and resistant to some insecticides.

Stewart recommends Orthene, Centric and Trimax for control of the pest. “All things being equal, I lean toward Centric because it shows a little better activity on plant bugs than the other neonicitinoids (a new class of chemistry).”

“Orthene is still a good material, and Bidrin is still a good material in most areas, but there is some resistance in some locations.”

The presence of other pests can also affect the choice of products, according to Stewart. “Early in the season, your material choice is going to be influenced by aphids. If you have a lot of aphids, you would be less inclined to use something like Orthene and more inclined to use Bidrin or one of the new neonicitinoids.

“When you get into mid-season, you're dealing with Bt cotton and potentially bollworms that have escaped Bt cotton or stinkbugs. The pyrethroids, especially in west Tennessee, have good activity on all three (plant bugs, stink bugs and bollworms).”

According to Michael Boyd, Extension entomologist at the Delta Center in Portageville, the Missouri Bootheel is planting more Bt cotton in 2003 in response to severe tobacco budworm infestations that occurred in conventional cotton varieties in 2002.

With boll weevil eradication also underway in the region, Boyd expects to see plant bugs become more prevalent. “But we don't have quite have the overwintering habitat for the stinkbug like they do in west Tennessee.”

New insecticides such as the neonicitinoids are good options for specifically targeting plant bugs while keeping beneficial insects, Boyd noted.

“Since we stopped spraying for boll weevils, our plant bug populations just exploded,” notes Len Doyle, a Somerville, Tenn., cotton consultant. “We also saw an explosion of stinkbugs.

“On the other hand, we've seen a lot more beneficials, also. That gives us a chance to use our beneficials as a tool.”

Doyle and his son, Clint, used neonicotinoid insecticides to combat the bugs. But Doyle cautions that not all members of the chemical family are created equal — growers need to select their insecticide based on its unique strengths.

Residual activity is another part of the insecticide decision. According to Doyle, “We saw about 10 days of residual control of plant bugs with Centric after the first application, and we saw every bit of 14 days of residual on aphids.”

Stewart says that although he recognizes that some growers rely on preventive applications of neonicotinoids, he favors the scout-and-treat approach for plant bug control.

“Growers really have to design their programs based on their capabilities and attitudes,” he says. “Some of these guys don't hire scouts. A prophylactic approach might be better for them than the alternative, which might be not treating at all, or just taking a guess. But I would like to see some scouting and evidence of an infestation before a spray is made.”

While neonicitinoids are easier on beneficial insects than other products used for plant bug control, “they're not exactly what I would call soft,” Stewart added.

“But they definitely are safer to handle than some of the other compounds. The downside is that they are little more expensive when you compare the best rates of Orthene and Bidrin to the best rates of the neonicitinoids.”


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