We are seeing damage from bermudagrass stem maggot (BSM) at this time and will have to start treating fields. I looked at this hay field in Boston last week. Colquitt County Agent Jeremy Kichler is reporting BSM in Alicia plots at the Expo.
The hay field will have a frosted appearance after the larvae (maggot) of the fly feed inside the shoot affecting only the top shoots (usually top 2). The lower shoots are not affected. The shoots stop elongating after feeding occurs. In the U.S., only bermudagrass is a host of BSM. Below are points I try to summarize from Biology & Management of Bermudagrass Stem Maggot. Click that link to read more detail.
The fly is small and yellow colored with dark eyes. The fly lays its eggs on the bermudagrass stem near a node. The maggot is yellowish in color and grows to be about 1/8 inch long. It may be hard to find the maggots, because they have usually left the stem by the time the plant shows symptoms of damage. There are multiple generations each summer. The fly has a life cycle that usually lasts about 3 weeks, but can be as short as 12 days.
One cultural option we have is to go ahead and cut the hay. UGA Extension Specialists Dr. Will Hudson and Dr. Dennis Hancock say if damage is found within 1 week of the normal harvest stage, go ahead and harvest the crop as soon as weather conditions allow. Once the damage becomes apparent, the crop is unlikely to add a significant amount of yield. If damage is observed within 1 to 3 weeks after the previous harvest, it is also likely that the crop will not add a significant amount of yield. The damaged crop should be cut and (if the yields are substantial enough to warrant) baled and removed from the field as soon as weather conditions allow. Leaving the damaged crop in the field will only compete with any attempts by the plant to regrow and decrease the opportunity that the next cutting will have to accumulate mass.
The most important insecticide spray is the first one which should occur 7 – 10 days after cutting. We then follow up with another application 7 days following this. Below is from Dr. Hancock:
We still do not have an insecticide that can successfully eradicate the invasive bermudagrass stem maggot (BSM). However, we have been able to suppress the fly population and the associated damage by the maggot when affected bermudagrass fields received two applications: 1) applying a pyrethroid (any labeled pyrethroid seems to work) as soon as the harvested bermudagrass begins to regrow (7 – 10 days after cutting) and 2) a second application 5-7 days later. Because of the expense of these treatments, these applications should only be made if a history of BSM damage would suggest that greater than 25% yield loss from the BSM is to be expected.