A new pest that can seriously damage bermudagrass hayfields is spreading throughout the South, researchers say.

Bermudagrass stem maggots have cut some producers’ hay yields in half, according to Will Hudson and Dennis Hancock, Extension specialists at the University of Georgia.

The insect, native to Asia, was first discovered in the U.S. in Georgia in 2010. But producers in Alabama, Texas, Louisiana, Mississippi, Tennessee, South Carolina and North Carolina also report having found the pest in their fields.

The good news: The Georgia researchers have had success controlling the fly that produces bermudagrass stem maggot with pyrethroid insecticides. They recommend one application a week after cutting, then a second about a week later at a total cost of about $10-12/acre.

“The fly is relatively easy to kill,” Hancock says, noting the second application is critical because there can be multiple generations within one cutting. The fly can be hard to find because it tends to stay near the soil surface. But there are telltale signs of infestation. Damaged bermudagrass fields look frosted, with leaf ends showing obvious insect damage, Hancock says.

The fly can be identified by its distinctive yellow abdomen and black spots with a gray thorax and transparent wings. Hudson suggests scouting for the pest beginning in April.

It lays eggs on the bottoms of leaves, and when they hatch, the maggots burrow down to the first node in the stem and feed on vascular tissue. The insect seems to prefer thin-stemmed varieties, says Lisa Baxter, a graduate student working with Hudson and Hancock. This may be because of short oral ridges on the larvae.

“If the larvae can’t penetrate the stem, it can’t go on to damage the shoot,” Baxter explains.

There is little literature about the pest’s biology, so Baxter is using information from the similar sorghum shoot fly to suggest that larva development improves as temperature and humidity increase, and that they likely lay their eggs at a height of about 5-8”.


 

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The insects have been first spotted in early June the last two years, with the damage beginning a little earlier each year since they were first noticed in 2010, Hudson says. The team will continue its research hoping to find answers to several questions.

“We’re having trouble determining what a threshold is and how many flies are required to do a certain amount of damage, because sampling these guys is pretty challenging,” Hudson says.

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