Texas Crop and Weather Update07/20/2017
Forage producers should be on the watch for and ready to act against two pests known for decimating hay fields – fall armyworms and Bermudagrass stem maggots, said a Texas A&M AgriLife Extension Service expert.
Dr. Vanessa Corriher-Olson, AgriLife Extension forage specialist, Overton, said she has been receiving calls and reports regarding fall armyworm and Bermudagrass stem maggot activity in East Texas and Central Texas pastures.
Armyworm numbers typically rise in the fall, but weather conditions, such as a dry spell followed by a rain event and cooler temperatures, can lead to flushes of the pest, Corriher-Olson said.
“They like cooler, moist conditions, and the last few rain events created the right environment for them,” she said.
The armyworm got its name because they appear to march across hay fields, consuming the grass in their path.
Producers should scout each morning for armyworms, she said. Armyworms are green, brown or black in color and can be identified by the white inverted Y on their head. They can grow up to 1 inch in length when mature.
The threshold for insecticide spray treating a pasture is three or more armyworms per square foot, Corriher-Olson said. Armyworms in those numbers should be treated immediately. Armyworms in the last two or three days of their larvae stage consume 85 percent of their diet.
Corriher-Olson recommends insecticides labeled for armyworm control in pastures and hayfields. She said applicators should always follow all label instructions on pesticide use and restrictions.
“Armyworms are principally night feeders and can do a lot of damage very quickly,” she said. “So we recommend that producers act immediately once they’ve seen armyworms reach the threshold.”
More information about armyworms can be found in AgriLife Extension entomologist Dr. Allen Knutson’s report The Fall Armyworm – Pest of Pastures and Hay at: http://foragefax.tamu.edu/files/2015/08/Armyworm-Fact-Sheet-2015.pdf.
Corriher-Olson said she had received several reports of Bermudagrass stem maggot, which hatch inside the grass stem and feed on the plant tissue, typically killing the top two leaves of the plant.
The stem maggot is difficult to scout, Corriher-Olson said. Maggots are typically not seen but become a small yellow fly, which is difficult to detect.
“Unfortunately, the way we typically detect stem maggots is by finding damage,” she said. “They typically kill the top two to three leaves, so If you look at your field and it looks like there’s been a frost event or you can pull the top two leaves from the stem very easily, you’ll want to take action.”
Corriher-Olson said producers should cut their hay meadow to reduce leaf, and therefore yield, losses once stem maggots are detected. Producers should follow by applying a pyrethroid insecticide seven days after the cutting to address the adult flies.
AgriLife Extension district summaries can be found here.
Source: Texas AgriLife Extension