Varieties influence cotton IPM

A decision most Southeastern cotton producers already have made — whether to plant Bt or conventional varieties — will greatly influence integrated pest management decisions this year, says Phillip Roberts, University of Georgia Extension entomologist.

“When deciding whether or not to plant Bt cotton, growers should have considered factors such as tobacco budworm populations, the threat of pyrethroid resistance and their ability to treat tobacco budworms and corn earworms in a timely manner and in the presence of high pressure,” says Roberts.

Pyrethroid-resistant tobacco budworms first were documented in Georgia in 1997 in Decatur County, he says. “Since that time, we've observed problems with control, and we suspect resistance or increased tolerance in other parts of the state,” he says.

Alternative insecticides such as Tracer and Steward are effective tools for managing pyrethroid-resistant tobacco budworms, he adds. However, foliar treatments must be applied on a timely basis.

“Larvae less than one quarter-inch in length, or three days old, must be targeted to achieve good control. Non-Bt acres should not exceed what can be sprayed in three to four days. If we experience high pressure, multiple insecticide applications may be needed on a five-day interval,” says Roberts.

Rain and other delays may inhibit a grower's ability to be timely and may reduce the effectiveness of insecticide applications, he says. “We have the tools to manage tobacco budworms and corn earworms on non-Bt cotton, but management will be more intensive. Regardless of technology, a good scout is a must. Good decisions can be made only when we have good scouting information.”

Many cotton producers in Georgia and other parts of the Southeast have increased their conservation-tillage acres in recent years, says Roberts, and variations in insect complexes can vary by tillage system.

“Many insects are unaffected by the tillage system — these include most mid- to late-season bug and caterpillar pests. Early season thrips populations generally are lower in reduced tillage. But a preventative insecticide at planting still is recommended.”

The risk of attack from some insects, especially cutworms, is increased in conservation-tillage systems, notes Roberts. The risk of cutworm pressure can be reduced significantly if winter cover crops or weeds are terminated at least three weeks prior to planting, he adds. If the cover is not terminated, cutworms may become established on plants and move to emerging cotton seedlings as host plants dry down.

“Observations and data suggest timely termination is especially important when legumes or winter weeds are used as the cover. In addition to cutworms, problems with false chinch bugs have been observed in recent years.

“Most problem fields have been in reduced tillage, and high populations tend to be associated with fields which were not burned down in a timely fashion. In situations where the risk of cutworm attack is high — following legumes or green vegetation present at planting — consideration should be given to applying a preventative cutworm treatment at planting. An economical approach would include banding a pyrethroid behind the planter.”

On a more limited basis, some fields have been observed with high populations of grasshoppers, says Roberts. “Timely termination of covers will help here but will not eliminate the threat of stand reduction from grasshopper feeding.”

An obvious difference in conservation-tillage is the buildup of fire ant populations due to the lack of soil disturbance, says the entomologist. Fire ants are an important predator of bollworm eggs and larvae.

“We consider fire ants to be one of the three most important predators, which also would include bigeyed bugs and minute pirate bugs. However, there's a slight negative associated with fire ants. Fire ants feed on honeydew excreted by aphids and will protect aphids so as to increase the presence of honeydew.

“The end result is that aphids tend to build populations more quickly in the presence of fire ants, but these same fields generally are the first in which aphids crash due to the naturally occurring fungus. The benefits of fire ants far outweigh this slight negative. From an IPM standpoint, termination of the winter cover at least three weeks prior to planting will reduce the risk of early season insect problems.”

A preventative insecticide at planting is recommended for early season thrips control, says Roberts. Several options are available, including in-furrow granules, in-furrow sprays and seed treatments.

A large percentage of Georgia's acreage is treated with Temik in-furrow, and Temik at 3.5 pounds per acre has proven to be a consistent performer, he says.

Commercial seed treatments offer convenience at planting and are an option for early season thrips management, says Roberts. Seed treated with Orthene provide control for about seven to 10 days while Gaucho and Cruiser (formerly Adage) will provide more extended control.

“However, these seed treatments have tended to be erratic in performance when compared to Temik. This erratic performance appears to be more common on April and early May plantings, when thrips populations generally are high and plant growth may be rapid.”

Regardless of the treatment applied at planting, it's important, says Roberts, that growers scout fields at least weekly and react in a timely fashion if the treatment if failing. Foliar sprays of Orthene, Bidrin or dimethoate are recommended when thrips number two to three per plant. Foliar treatment rarely is necessary after plants have five true leaves and are growing rapidly, he says.

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