A relatively new pest – the Bermuda grass stem maggot – is plaguing Texas hay producers this season, according to Texas A&M AgriLife Extension Service experts.
However, new research from Texas A&M AgriLife is helping growers better manage this pest.
Using data from fields in North Texas, Dr. Allen Knutson and Dr. Forrest Mitchell, Texas A&M AgriLife Research entomologists, Stephenville, developed guidelines as to when an insecticide treatment is justified based on the cost of treatment and value of hay.
Dr. Vanessa Corriher-Olson, AgriLife Extension forage specialist, Overton, said she has received numerous phone calls and emails from producers and reports from AgriLife Extension agents in the region regarding the pest. She has also found them in hay and forage pastures at the Texas A&M AgriLife Research and Extension Center at Overton.
Feeding by the stem maggot causes the death of the top two to three leaves while the rest of the plant remains green. This gives a stand of Bermuda grass the appearance of frost damage. Also, the discolored top leaves are easily pulled from the leaf sheath, and plant growth is stunted.
The new guidelines consider the cost of insecticide and the value of hay in determining when insecticide treatment is economically justified, Knutson said.
In fields where stem maggot damage is already extensive, an insecticide treatment may not be sufficient to get the crop growing again, Knutson said, because damaged stems shade the lower nodes, preventing regrowth of new shoots. In this situation, the hay should be cut and removed as soon as possible to allow sunlight to stimulate regrowth.
A pyrethroid insecticide should be applied seven to 10 days after cutting to protect the regrowth from another stem maggot infestation.
The Bermuda grass stem maggot is an invasive pest native to southern Asia and was first reported in Georgia in 2010. The pest has been found in Texas since 2012.
This pest only infests Bermuda grass and stargrass, Corriher-Olson said. The fly, which is yellow with a black head, lays its eggs inside the Bermuda grass stem. After the egg hatches, the larva, or maggot, which is white with a black head and 1/8th to 3/16ths inch long, moves to the last plant node and begins consuming the plant material within the stem.
Guidelines on managing Bermuda grass stem maggot and the table of treatment thresholds for a range of control costs and hay values are available online at https://foragefax.tamu.edu/.
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