Secondary pests moving to forefront

Early spring weather patterns this year have resulted in a Mid-South cotton crop that ranges from emerging seedling to cotton that's reached the three-leaf stage, often in fields side-by-side. That could mean a longer insect control season and increased pest pressure late in 2002, according to entomologist Gordon Andrews.

Once relegated to second-class status, stinkbugs and plant bugs are emerging as two of the primary pests Delta cotton growers can look forward to battling each year. The advent of Bt cotton and the boll weevil eradication program have further elevated the status of these pests.

“Both Bt cotton and the eradication program reduce the number of insecticide sprays needed to raise cotton. We're successfully controlling worms and weevils, but plant bugs and stinkbugs seem to be filling the gap in this unsprayed environment,” says Andrews, an Extension entomologist at the Delta Research and Extension Center in Stoneville, Miss.

“They were always there, we're just not controlling them as well, because we're not applying as much insecticide to the cotton crop. In the past, we may have tolerated more plant bug damage because we were trying to protect as many beneficial insects as possible in our attempt to control bollworms. And certainly in past years, the stinkbugs were controlled by worm and weevil control applications.”

The likelihood of increased pressure from secondary pests like stinkbugs and plant bugs mean growers need to be extremely diligent in scouting their cotton fields, Andrews says.

“It's essential that you make sure the populations of these pests don't get high enough to damage yields.”

According to Mississippi State University's 2002 Cotton Insect Control Guide, plant bug treatment thresholds vary according to the growth stage of the cotton crop and the scouting method used.

  • Early-season plant bug populations should be treated with a foliar insecticide if you find one plant bug-flagged plant and one or more plant bugs per 10 row feet.
  • During the first two weeks of squaring, plant bug thresholds vary from one bug per 6 feet of row for a drop cloth, to five bugs per 100 terminals scouting visually, to eight bugs per 100 sweeps using a sweep net.
  • From the third week of squaring to first bloom, those threshold levels increase to two bugs per 6 feet of row, 10 bugs per 100 terminals, and 15 bugs per 100 sweeps.

“The sweep net is a very effective tool for monitoring adult plant bug populations, but the ground cloth is more effective for monitoring nymphs. Thorough scouting requires the use of both the sweep net and ground cloth. Visual scouting is a less-reliable method of sampling for plant bugs, but may be less time-consuming. Prior to first bloom, sample fields twice weekly for plant bugs,” the guide recommends.

After first bloom, the insect control guide recommends treating when plant bug populations exceed three bugs per 6 feet of row using a drop cloth, or 15 bugs per 100 plants when scouting visually.

“After plants begin to bloom, effective use of the sweep net and ground cloth becomes more difficult and more emphasis is placed on visual scouting,” the insect control guide says. “Scout by examining randomly selected plant terminals for the presence of adults or nymphs and by checking inside squares, blooms, and small bolls for the presence of nymphs.”

Foliar insecticide options for plant bug control include Centric, Orthene, Bidrin, Provado, Fyfanon, Monitor, Vydate and Curacron.

Treatment thresholds for plant bugs may vary by region, going from north to south in the Cotton Belt. Acceptable threshold levels may be lower in shorter-season cotton and/or in non-irrigated cotton. In these situations, the grower is often trying to make a crop more quickly, and as a result, the cotton plant has less time to compensate for damaged fruit.

While stinkbugs cause essentially the same type of damage to cotton plants as plant bugs, they cause greater damage per feeding and damage mature bolls. Therefore, individual insects cause more yield and quality loss.

“Plant bugs feed on the smaller, younger bolls, but stinkbugs can feed on cotton bolls almost until the seed matures,” Andrews says. “Stinkbugs also tend to inject more salivatory fluid into the boll, increasing the amount of boll damage.”

According to the Mississippi Insect Control Guide, the threat of stinkbug damage is more prevalent in Bt cotton or in those areas where the boll weevil has been eradicated because of the related need for fewer mid- to late-season insecticide treatments.

“High numbers of stinkbugs can develop in crops such as corn, sorghum, or early-maturing soybeans and then migrate into nearby cotton during late season. Intensify scouting for stinkbugs when nearby alternative hosts begin to mature or when scouting for these pests in Bt cotton.”

Other emerging pests Delta cotton growers may have already encountered are cutworms, flea beetles and aphids.

“The spring burndown associated with minimum and no-till production systems may permit these pests to jump from overwintering hosts to cotton, further building populations,” Andrews says. “If an early-season insecticide treatment is needed to control plant bugs, growers should consider the aphid populations in their fields when choosing a pesticide product to avoid inflaming aphid populations.”

e-mail: [email protected].

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