I was informed by a producer on Wednesday that he had discovered Bermudagrass Stem Maggot in his hay field. I wanted to share this alert with you so you will be aware that we may be seeing more of this invasive pest earlier this season. The bermudagrass stem maggot results when the adult fly (small and yellow with dark eyes) lays its eggs on the bermudagrass stem near a node. You will not usually find the maggot (about 1/8″ long and yellowish) because they usually have left the stem by the time the grass shows symptoms of damage. The fly has a life cycle that can last up to 3 weeks or short as 12 days.
This pest has become a serious concern among cattlemen and hay producers and is having a major impact on hay production in South Georgia. In the U.S. bermudagrass stem maggot is only a problem on bermudagrass and stargrass. After the egg hatches, the maggot will work its way to the last plant node. While the maggot grows, it will burrow into the shoot and feed. The result is withering, chlorosis, and death of the leaves (top 2-3 leaves). The death of these upper leaves with the lower leaves remaining green will cause a frosted appearance. Damage will be worse in finer stemmed varieties of bermudagrass such as; Russell, Coastal, Alicia, and common Bermuda. Some hybrids are less susceptible, such as Tif 85, because they are coarser stemmed. The most damaging economic losses may occur during growth periods that are limited due to poor soil and moisture conditions. If you have good soil and soil moisture this will allow more normal rapid growth and the loss of the upper 1-3 leaves will have minimal impact on yield. Keep in mind that grazed pastures are not normally affected by the fly because as livestock graze, they eat the fly eggs and maggots along with the grass. So, unless your grazing pressure is light the population of the fly will not build up. The following information provided by Dr. Dennis Hancock (UGA Forage Specialist) is recommended management strategies. Dr. Hancock states that it is important to remember that the following treatment will only suppress the problem but not eliminate the pest.
*If damage is found within 1 week of the normal harvest stage, harvest the crop as weather allows. Once damage is found the crop is not likely to add any significant yield.
*If damage is found within 1-3 weeks after the previous harvest, the damaged crop should be cut, baled (if there is enough yield), and removed from hay field as soon as weather allows.
*Apply an insecticide (lowest labeled rate of any Pyrethroid approved for hayfields) a few days up to one week after harvest. This application will kill existing flies.
*Follow with an additional application of labeled Pyrethroid one to two weeks later.