Burke – Jenkins Ag News

Bermuda Grass Stem Maggot

As of late last week areas in the southern parts of the state were seeing significant damage from the bermudagrass stem maggot. We are starting to see increases in damage in our area. I have attached the latest management strategies from the “Bermudagrass Stem Maggot Research Update.”
Management Recommendations
If signs of BSM damage occur near the end of a regrowth cycle (within 2.5-3 weeks after cutting or grazing), the producer should harvest or graze the field as soon as conditions become favorable. Damage seen earlier in the growth cycle will very likely substantially reduce agronomic performance of the crop. Once a stand that is 6 inches or taller has been damaged by BSM feeding, the only option is to cut and/or graze the stand to a height of 3-4 inches and encourage regrowth to occur because the bermudagrass crop is unlikely to further develop. Instead of having a low-yielding, severely damaged crop that provides a haven for a large fly population build up, it is better to cut the field early and accept the loss. Ideally, the infected material should be removed from the field to prevent shading of any regrowth. The larvae do not appear to remain in cut stems. Within hours of cutting, larvae will exit damaged stems and travel to the soil. Those larvae that are mature enough to progress will pupate and emerge from the soil approximately 10 days later. Flies in fields that have been harvested escape to field margins and neighboring bermudagrass fields. Chemical control of the BSM larva is challenging because it is inside the pseudostem and no systemic insecticides are approved for use in pastures or hay crops. Suppression of the BSM fly is also challenging because the flies are mobile. In addition, one must consider the limits of a chemical application in canopy penetration. In general, the BSM flies tend to remain deep in the canopy except to move from one location to another or in response to a disturbance. The recommended chemical suppression technique is to apply an insecticide after the bermudagrass has begun to regrow (7-10 days after cutting) following an affected harvest. A second application can be made 7-10 days later to suppress any flies that have emerged or arrived since the last application. Chemical actions should be taken if there is a known history of BSM damage to the bermudagrass and the expense of the applications (usually less than $15/acre for both applications) is justified by the forage yield saved. Populations have not yet been high enough to warrant chemical suppression prior to the first bermudagrass hay cutting (or equivalent timing if the crop is to be grazed). Usually, the chemical suppression technique is not necessary until after the second cutting. In general, one application of insecticide 7- 10 days after the second and third cutting (and any subsequent cuttings) has kept the damage to below economically significant levels.
Source- http://www.caes.uga.edu/commodities/fieldcrops/forages/documents/GCA1605.pdf