By Mary Sowerby

UF/IFAS Regional Dairy Extension

It seems it is not just people who like to transplant themselves to Florida. One of the latest immigrants, now found in hayfields throughout Florida, is a tiny invasive fly called bermudagrass stem maggot. A native of Japan, Indonesia, India, and Hawaii, the fly was originally discovered in the Continental United States in 2010 in three counties in Georgia. It has since spread throughout the southeast from Louisiana to Tennessee to Florida. 

University of Florida Entomology Professor Russ Mizell, notes, “The immature bermudagrass stem maggot flies infest the terminal stems of bermudagrass of all types, retarding growth of the grass stem due to dieback of the terminal.” 

This causes loss of both quality and quantity of hay and pasture. Fields infected by the stem maggot look frosted brown in the middle of summer when they should be green. 

The bermudagrass stem maggot larvae can be detected in grass stems by splitting the stems down the middle from the tip to the first node. Dr. Mizell stated, “Early stage larvae will be found in green stems and late stage larvae in stems which appear to turn color on one side while the other side of the stem remains green. Previous infestation of stems that are brown and appear dead can be determined by gently pulling the dead tip out of the stem and looking for evidence of maggot feeding. Mature bermudagrass stem maggot larvae leave the stems to pupate in the soil and emerge as adult flies in a week to 10 days.”

Georgia Forage Extension Specialist Dennis Hancock has found thicker-stemmed varieties of bermudagrass, such as Tifton-85, seem to have fewer stems affected by stem maggot damage than the thinner-stemmed varieties, such as Alicia.     

Georgia producers and researchers have reported some success deterring the fly by using two applications of pyrethroid insecticides (at one week after the last mowing and about two weeks later). However, the large number of flies and ease with which they move between fields lowers the effectiveness of this method of control. Since the larval stage and plant damage occur inside the plant’s pseudostem, a systemic insecticide would be needed to kill the larvae. Unfortunately, livestock eating the treated grass would be as likely to ingest a systemic pesticide as the fly larvae, so it is unlikely a systemic insecticide will be developed for the problem.

Harvest management is the best method of mitigating stem maggot damage. Dennis Hancock recommends that, “If damage is found within one week of the normal harvest stage, proceed to 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 one to three weeks of the previous harvest, it is also likely the crop will not add a significant amount of yield.

“The damaged crop should be cut and (if 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.” 

To assist University of Florida researchers study bermudagrass stem maggot more thoroughly, please contact your local county agriculture agent (Elena Toro in Suwannee County at 386-362-2771) or email Liza Garcia-Jimenez at lizagracia@ufl.edu with the location and type of bermudagrass grown in any field found infested with the pest. It is also requested that those with bermudagrass stem maggot in their hayfields visit the following website:  https://qualtrics.com/SE/?SID=SV_8kAvLs6iLXdk0nj and fill out the survey found there so more can be learned about this new pest. 

For more information, check out the GeorgiaForages YouTube video about Bermudagrass Stem Maggot at:  m.youtube.com/watch?v=fx03U or the July 2012 Georgia Cattleman article by Dennis Hancock.

Extension programs are open to all people regardless of race, color, sex, religion, disability or national origin.  In accordance with the Americans with Disabilities Act, any person needing a special accommodation to participate in any activity should contact the Suwannee County Cooperative Extension Service at 1302 Eleventh Street, SW, Live Oak, Florida 32060 or telephone (386) 362 – 2771 at least five working days prior to the event.  Hearing impaired can access the previously mentioned telephone by contacting the Florida Relay Service at 1 – 800 – 955 – 8770 or 800 – 955 – 8772 (TDD).