Add Texas to the list of Southern states hit by the bermudagrass stem maggot. The pest was found earlier this month in Van Zandt County, confirms Vanessa Corriher-Olson, a forage specialist with Texas A&M AgriLife Extension.

Native to southern Asia, the stem maggot was first discovered in the U.S. in Georgia in 2010. Since then, it’s been sighted in a handful of other Southeastern states.

“Basically, they consume material inside the stem, unlike armyworms or grasshoppers, where the damage is external,” notes Corriher-Olson, who is based in Overton.

Adult flies lay eggs on bermudagrass stems near nodes. Their larvae, which grow to be about 1/8” long, look like pale yellow maggots. They burrow into grass shoots to feed, causing the top two to three leaves to wither and die.

To see maggots and the brownish feeding sites on stems, growers have to cut stems open just below the dead leaves.

The adult flies, which are small with dark eyes, may go unnoticed. So may the early stages of an infestation, adds Corriher-Olson.

“People are not going to realize they have the pest until they see the damage. It looks similar to what you might see from a light frost. Stem tops are whitish or lighter in color than unaffected plants. Only the top parts of the shoots are damaged. The lower leaves on the shoots remain green. The leaves above the feeding sites wither and die.”

There can be several generations of the pest each summer. The fly’s life cycle is usually about three weeks, but it can be as short as 12 days.

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Yield loss appears to depend on growing conditions. “Typically, damage is more likely to be found in a hay meadow, not in a grazed field, because the flies won’t have time to complete their life cycle,” Corriher-Olson says.

Management depends on how near the hay crop is to harvest when damage is identified. “If damage is found within one week of harvest, the recommendation from Georgia (researchers) is to harvest as soon as possible. The longer the wait, the more likely the damage will spread, and there will be further reduction in yields.”

If the pest and damage are confirmed one to three weeks after the previous harvest, the recommendation is to cut, bale and remove damaged grass from fields. “The only threat posed by leaving the hay in the field is that it’ll compete with any attempts of the plant to regrow, therefore decreasing the yield of the next cutting. Leaving the hay in the field does not increase infestation. It’s unlikely that the damaged areas will contribute significantly to yields during the next harvest.”

The pest can also be controlled with foliar applications of several inexpensive insecticides. While economic thresholds for treatment in Texas have not been established, current recommendations are to treat after a cutting if damage levels are high.

For more on stem maggots as well as other bermudagrass pests causing problems in the Southeast, read "Multiple Pests Strike Southern Bermudagrass."

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