The Bermudagrass Stem Maggot has been with us for several years now and most everyone knows how to scout for damage and how to treat. However, in the last week there has been a significant increase in Bermudagrass Stem Maggot activity in fields. I am finding thousands of BGSM flies in most fields. This means damage is just around the corner, if you are not already seeing some. If you have noticed small patches or even individual plants that are turning yellow and dying in your bermudagrass fields? There is a very good chance you have an infestation of the Bermudagrass Stem Maggot (BGSM).
Bermuda stem maggot damage looks much like frost damage on your bermuda. The tips will turn brown and look like they have had a light frost. On infected plants, if you pull the top leaf or two it will slip out very easily, and you can see the damage at the base of these leaves on the stems. This damage is a result of the bermuda stem maggot fly laying eggs on the bottom side of the leaf, once hatched the maggot will go to the node, burrow itself inside the stem and feed on the vascular tissue, causing death to the top one to three leaves. With the wet summer and green grass this year the damage is becoming more noticeable.
Forage is plentiful this year and treatment may not be a cost you want to incur, but if hay yields are important to you yield reductions can exceed 50%. With this much potential loss treatment certainly is feasible depending on the stage of growth of your grass, and the intensity of the infestation. However, due to the insect having multiple generations during a growing period, control can be difficult. If you start seeing damage and your hay is close to ready to cut, go ahead and cut it. Then you can begin treatment following cutting. The current recommended treatment consists of two separate applications of a pyrethroid insecticide. The first application should be made 7 days following hay harvest. The second application should be made one to two weeks following the first application. If your field has no history of the stem maggot then do not spray. Fields that are grazed are rarely affected by BGSM, this is because the cattle tend to keep the young tender leaves grazed off, leaving the BGSM fly nowhere to lay her eggs.
One interesting bit of information about the bermuda stem maggot is that it seems to prefer finer stemmed bermudagrasses over those that are more course stemmed. Bermudagrasses like Coastal, common or Alicia will have a higher incidence of infection than Tifton-85.