Mississippi hay producers have a new insect pest to contend with in their efforts to produce high quality bermudagrass hay. Bermudagrass stem maggot, BGSM, was first detected in Georgia in 2010 and by fall of 2012 had spread throughout Mississippi. Adults are small flies, about half the size of a house fly, with yellow abdomens, but it is the legless white larvae that cause damage—by boring into the growing shoot tip and killing it. Damage is restricted to the two or three grass blades at the tip of the growing shoot because the larvae do not feed past the first internode. When viewed from a distance, heavily infested fields look like they have suffered light herbicide injury or experienced an early frost. Low infestations are relatively inconsequential, but heavy infestations can stop a field from growing, resulting in significant yield loss. Although this little fly readily attacks all types of bermudagrass, including turf-type bermudas, it is only a concern in highly managed bermudagrass hay fields. Grazing or frequent mowing prevents infestations in pastures and lawns by removing the stem tips in which the larvae feed. Grasses other than bermudagrass are not attacked.
Control: BGSM can be controlled by spraying recently harvested fields with low rates of pyrethroid insecticides such as Mustang Max, Baythroid, or Karate Z. Apply the first spray 5 to 7 days after the field was cut, and follow with a second spray 5 to 7 days later. The objective is to kill adult flies before they can lay eggs and/or to kill hatching maggots before they bore into the stem. Currently, there are no insecticides labeled for use in hay and pasture crops that will control the maggots once they are inside the stems. The need for treatment is determined by the level of stem infestation experienced in the previous cutting. If 15 to 20 percent or more of the stems were infested in the last cutting, it is probably a good idea to treat the next cutting.
See the Bermudagrass stem maggot page for more photos of this new pest and specific control recommendations.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.