Historically, the SWCB has been the major borer problem in the northern parishes, whereas the SCB 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 were sporadic and somewhat unpredictable for corn acreage planted during the recommended planting windows. Last year, however, was a major exception to most of these trends.
In 2002, the SCB became a serious, and in some cases the predominant borer pest of corn in Catahoula and Concordia Parishes and to some extent in Tensas and Franklin Parishes. It appeared that the SCB became less important as the corn acreage move northward from the lower Delta parishes. The SWCB was a bigger problem in the northern most parishes, where it also resulted in heavy infestations. By the end of the growing season, heavy infestations of both borers had moved into late-planted grain sorghum. Heavy SCB infestations also developed in rice during late season.
It is difficult to predict whether or not 2003 will see a repeat of the heavy borer infestations experienced in 2002. The factors causing the 2002 epidemic are not fully understood, but we are hopeful that the hard winter freezes have reduced overwintered populations of the SCB.
There are some preventive measures that producers can take 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 early planting a high priority. As with other crops and other pests, the corn borer problem is a race between crop development and the build up of borer populations during the course of the season. Early planting may not guarantee you total escape from borers, but late planting 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 based on yield performance at various research stations. These hybrids are Terral 2155, Terral 2160 and Pioneer 31B13. 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 SWCB and the SCB at all crop growth stages.
The disadvantage to Bt hybrids is the up-front cost, which may not be recouped in the event of 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 one-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.
We anticipate that compliance with this program will be strictly monitored in 2003. Strip planting non-Bt corn with Bt corn might inhibit or reduce the build-up of borer populations on the non-Bt strips, but it will also complicate insecticide applications if treatment for borers in the non-Bt strips 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 also inhibit borer population build-up 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 then attempt to 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 properly timed 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 recommendation for borer control in corn for 2003. This product represents a different chemistry, which provides improved residual control.
Although research in corn to document the extent of this residual effectiveness is lacking, Intrepid research in other crops indicate that two to three weeks of effective residual might be a reasonable expectation. If so, this 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 pheromone 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 pheromone trap and lure bait commercially available for the SWCB, but not for the SCB.
Therefore, the use of SWCB pheromone traps in production areas, which also have high numbers of SCB, can be very misleading. Low trap counts may indicate low SWCB populations, but they say nothing about SCB populations in the same field.
Jack Baldwin is an Extension entomologist with the Louisiana State University AgCenter. e-mail: firstname.lastname@example.org