Bermudagrass Stem Maggot Management: Bermudagrass hay producers need to be out scouting their hay fields for bermudagrass stem maggot damage. I have noticed damage in some Colquitt County hays fields this week (6-21-16). According to Dr. Dennis Hancock, reports of bermudagrass stem maggot are starting to come in from south Georgia. Let’s discuss some management tips for this pest.
Bermudagrass stem maggot (BSM) is a new pest for Georgia forage producers. Damage from BSM is a bronzing of the bermudagrass, generating damage similar to that of severe drought or frost damaged bermudagrass. The bronzing was the result of chlorosis and necrosis in the top two to three leaves of the plant. The damaged leaves could easily be pulled from the sheath and the end inside the sheath either showed evidence of insect damage or obvious decay. This damage was clearly not that of abiotic stress but rather a consequence of larval feeding. Examples of the damage from BSM are in the slide below.
The figure above shows “Bronzing” of bermudagrass hay fields as a result of bermudagrass stem maggot damage (A). The bronzing is the result of damage done at the uppermost node that results in senescence of the top two to three leaves of the plant (B). The damaged leaves can easily be pulled from the sheath and the end inside the sheath shows evidence of insect damage from obvious decay (C).
Photo credits: A: Will Hudson, University of Georgia Entomology Dept.; B and C: Lisa Baxter, University of Georgia Crop and Soil Sciences Dept.
The current recommended chemical suppression technique is to apply a recommended rate of an inexpensive pyrethroid insecticide after the bermudagrass has begun to regrow (7-10 days after cutting) following an affected harvest. A second application should 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 two applications (usually less than $15/acre for both applications) is justified by the forage yield saved.
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 reduce agronomic performance of the crop substantially. 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. It is better to cut the field extremely early and accept the loss than to have a low-yielding, severely damaged crop that harbors a large fly population and leads to a further buildup. Ideally, the infected material would 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.
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