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Farmers preparing for corn borers

As Louisiana corn producers prepare for the coming season they should remember that last year the southwestern corn borer and sugarcane borer were serious pests in some corn-producing areas of the state.

The southwestern corn borer usually has been the major borer problem in the northern parishes; the sugarcane borer has been the primary borer problem in areas of south Louisiana where corn was grown in the vicinity of sugarcane. In both cases, economic infestations usually are sporadic and somewhat unpredictable for corn acreage planted during the recommended planting windows.

2002, however, was a major exception. The sugarcane borer became a serious problem (in some cases the predominant borer pest of corn) in Catahoula and Concordia parishes and to some extent in Tensas and Franklin parishes. The sugarcane borer became less important as one moved northward from the lower Delta parishes.

The southwestern corn borer was a bigger problem in the northernmost parishes, where infestations were heavy.

By the end of the growing season, heavy infestations of both borers had moved into late-planted grain sorghum. Heavy sugarcane borer infestations also developed in rice late in the season.

It is difficult to predict whether or not 2003 will see a repeat of the heavy borer infestations. The factors causing the 2002 epidemic are not fully understood, but we hope the hard winter freezes have reduced overwintered populations of the sugarcane borer.

Producers can take some steps to prevent a recurrence of last year's borer problems.

The first is to plant the crop early or within the recommended planting dates. Granted, corn planting is always weather-dependent, but producers should make planting early a high priority.

As with other crops and other pests, the corn borer problem is a race between crop development and the buildup of borer populations during the course of the season. Planting early may not guarantee a total escape from borers, but planting late will almost always guarantee heavy infestations during critical stages of crop development.

A second option is the use of Bt hybrids. This year Extension recommends three medium-maturity Bt hybrids — Terral 2155, Terral 2160 and Pioneer 31B13 — based on yield performance at research stations. These hybrids were recommended at all test locations around the state except Baton Rouge.

Recommended hybrids with the Bt technology provide excellent control of the southwestern corn borer and the sugarcane borer at all crop growth stages.

The disadvantage to Bt hybrids is the up-front cost which may not be recouped in a light borer year.

Producers who plant Bt corn are required to follow a resistance management program which requires them to plant at least a 50 percent refuge of non-Bt corn. The refuge must be located within a half mile of the Bt corn, if it is a separate field.

Other refuge options include blocks of non-Bt corn within the Bt field and strips across the Bt field of at least four to six rows of non-Bt corn.

I anticipate compliance with this program will be strictly monitored in 2003.

Strip-planting non-Bt corn with Bt corn might inhibit or reduce the buildup of borer populations on the non-Bt strips, but it will also complicate insecticide applications if a treatment for borers in a non-Bt strip is required.

Another option for preventive borer control is the use of Regent 4SC at planting as a soil insecticide treatment. LSU AgCenter research indicates that this systemic insecticide will control or suppress second-generation stalk borers. This would provide protection during some of the most susceptible crop development stages and inhibit borer population buildup within a field.

The use of Regent is not as effective as a Bt hybrid, but the up-front cost can be offset by its other service as a soil insecticide for certain soil insects.

The final alternative is to plant a non-Bt corn hybrid and scout and treat as needed. This is probably the most difficult alternative, because borer infestations are very difficult to detect before the larvae bore into the stalks. Scouting for egg masses and small larvae is a very tedious and time-consuming process that often provides poor results.

Larvae can be controlled with numerous insecticides, but applications must be timed properly so that the borers are still exposed to the chemical. Insecticide treatments are not effective after the larvae have bored into the plant.

Intrepid is a new insecticide recommended for borer control in corn for 2003. This product represents a different chemistry which improves residual control. Although research in corn to document the extent of this residual effectiveness is lacking, Intrepid research in other crops indicates that two to three weeks of effective residual might be a reasonable expectation. That would allow a wider window of crop protection and reduce, to some extent, the need for precise application timing in order to achieve effective control.

Scouting efficiency can be improved through the use of pheremone traps that attract and collect adult moths. Moth counts can provide a general idea of insect activity in the adjacent field, thus aiding in treatment decisions.

There is a very effective pheremone trap and lure bait commercially available for the southwestern corn borer, but not for the sugarcane borer. Therefore, the use of southwestern corn borer pheremone traps in production areas which also have high numbers of sugarcane borer can be very misleading. Low trap counts may indicate low southwestern corn borer populations, but they say nothing about sugarcane borer populations in the same field.

Jack Baldwin is an LSU AgCenter entomologist.

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