Ten Years of Bermudagrass Stem Maggot Research at UGA

Summary

The bermudagrass stem maggot (BSM) was first reported in Georgia in 2010. Damage has since been reported as far north as Kentucky and as far west as Texas. Ten years later, the BSM continues to be a major pest problem in Georgia and throughout the Southeast. Although the degree of damage depends on the bermudagrass variety, latitude of the farm, and time of year, producers have reported up to an 80% yield loss in late summer.

Situation

It is estimated that the bermudagrass stem maggot (BSM) negatively impacts the production of at least 75% of the approximately 4 million acres of forages in Georgia. Bermudagrass hayfields and pastures will appear “frosted” in the middle of summer because of the damage. The bronze coloration is consistent with frost damage, but it is clearly the wrong time of year for such discoloration. Upon closer inspection, it is clear that the damage is restricted to the top 2-3 leaves of the plant and was the consequence of larval feeding from a pest later identified as the BSM. When the BSM was recognized as a major pest in Georgia in 2012, the information available on the BSM would fit on one side of one page of notebook paper.

Response

Preliminary screenings revealed that the BSM damage was more severe in finer bermudagrass varieties such as Coastal and Alicia. In 2012, a greenhouse study was designed to test the BSM damage response on eight of the most popular bermudagrass varieties including a range of stem thicknesses. Varieties with C. nlemfuensis (stargrass) influence had fewer damaged stems and a lower percentage of damaged stems. This difference was credited to the larger stem size found in Tifton 85 and Coastcross II. Our initial chemical control recommendation was to spray pyrethroid insecticide 7-10 days + 14-20 days after harvest at labelled rate. This was based on the initial life cycle constructed by Dr. Will Hudson where the first flies would emerge from pupation 7-10 days after you cut and removed the hay. With each year, we continue to improve the effectiveness of our management recommendations. Through repeated field trials, we have observed a general seasonal trend in BSM damage. The damage tends to be most severe from July to mid-September. Although we may see BSM damage before then, it may not be economical to apply insecticides. We have worked with a team of County Extension Agents since 2017 to better understand the BSM’s behavior and adjust our management to improve insecticide effectiveness. Because of on-farm research efforts we now know that chemical applications should be applied before the dew dries, with the spray boom set as low as possible, and with at least 12-15 gallons of water per acre to ensure canopy penetration. This increases the likelihood of the BSM coming into contact with the insecticide. As we begin to explore the influence of forage management practices on BSM damage we are seeing a possible interaction between the BSM damage, harvest timing and height, fertilization, and weed control. What started as a search for chemically controlling a novel insect in bermudagrass, has expanded into a nexus of forages, weed and insect management, and soil fertility! We still have a long way to go, but the University of Georgia is recognized globally as the leading institution for BSM research. We have made a lot of progress in the last decade, especially in the last 3-4 years. There are now have a multitude of popular press and peer-reviewed papers available on the BSM, in addition to presentation and video materials available to County Extension Agents to educate producers in their local areas.

Impact

It is clear that a strategic IPM and forage management plan is key for our Southeast forage producers, especially when you consider the economic implications. The economic impact of the BSM damage depends on several factors, but if a conservative annual yield loss of 25% is generally applied to just the bermudagrass acreage in Georgia, the potential economic loss totals $30-40 million annually! In a recent economic evaluation, we found that the BSM may cause yield and economic losses, but unnecessary insecticide applications are more costly! Let’s assume we have a 100 acre hay field of a fine-stemmed bermudagrass (Alicia, Coastal, Russell, or Tifton 44). If we applied insecticide weekly, we would have a ~$13,000 seasonal net loss despite 15-20% yield increase in finer varieties during peak season. If left entirely unsprayed, the same field would have still generated ~$4,000 in profit! This example is certainly extreme, but it illustrates the importance of judicious insecticide application. Although our Extension programming was limited in 2020, survey results showed that producers expected to save $11.40/ac annually if they implemented the knowledge they learned from our forage Extension programming. If we applied this to the approximately four million acres of pasture, hay, and silage in Georgia, we would reduce producer costs by 45.6 million dollars annually! On-farm demonstrations and producer involvement in research activities will continue to improve adoption rates of good management practices, new technologies, and research-based solutions.

State Issue

Plant Production

Details

• Year: 2020
• Geographic Scope: State
• County: Tift
• Location: Coastal Plain Station, Tifton
• Program Areas:
  • Agriculture & Natural Resources