“This field of bermudagrass has just stopped growing, and we can’t figure out what’s wrong. The last cutting was pretty good. We didn’t notice any problems then.”
Mississippi hay producers have a new insect pest to contend with in their efforts to produce high quality bermudagrass hay. Bermudagrass stem maggot 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 a 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.
Light infestations of stem maggots often go un-noticed and cause relatively low yield losses, but moderate to heavy infestations can cause yield losses ranging from 30% to complete loss. The only way to restart a field that has stopped growing due to stem maggots is to cut the grass, remove any hay that can be harvested, and start spraying the next cutting as soon as it begins to grow.
Control: Stem maggots 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, or as soon as new growth begins to appear, and follow with a second spray 5 to 7 days later. The goal is to kill adult flies before they can lay eggs and 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 10% to 15% 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 of the Insect Pests of Hayfields and Pastures Website for more photos of this pest and more details on control.
Thanks to Mr. Lee Withers for sharing this photo of bermudagrass stem maggot damage.
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.
Mississippi State University is an equal opportunity institution.
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