Drought changes management strategy for Bermuda grass stem maggot

By for CAES News

Drought-like conditions this summer are forcing Georgia forage farmers to delay treatments for Bermuda grass stem maggot, according to Lisa Baxter, University of Georgia Cooperative Extension forage specialist.

It is normally recommended that farmers wait seven to 10 days after harvest, then apply a pyrethroid insecticide labeled for forages at the recommended rate, then repeat treatment seven to 10 days later.

A lack of rain across the state this summer calls for that treatment timeline to be tweaked, Baxter said.

“The problem is that, in a drought, we don’t have green leaves seven days after harvest. If there aren’t green leaves, there are no adult flies out there and that is what the pyrethroid is killing — the adult flies — not the other stages of the stem maggot,” she said.

For this reason, Baxter is recommending that Georgia forage producers hold off on the first treatment if they are experiencing below normal rainfall. 

“It feels good to put out the chemical like it says to on the calendar, but if the grass doesn’t match that, we’ve got to wait,” she said.

Most producers harvest on a 28-day interval, while some try to stretch their harvest window to 35 days to attempt to harvest more hay, although the quality may drop, Baxter said.

According to the U.S. Drought Monitor, parts of Georgia are experiencing abnormally dry conditions, especially in middle Georgia around Houston County. Little rainfall equates to slow growth for forages, especially if they’re not being irrigated.

“The way the damage happens, the fly has to lay its egg on a leaf. When the egg hatches, the larvae go into the stem and chew around in there, which is what kills the top (of the plant). If there are no green leaves for flies to lay eggs on, the whole life cycle stops,” Baxter said.

Baxter has delayed some research trials and Extension demonstrations on lightly irrigated plots because there wasn’t enough growth to treat with insecticide.

Bermuda grass stem maggot was first discovered in southern Georgia in 2010 and is a persistent problem for hay producers. Baxter said that the pest appeared earlier this year because of unseasonably warm temperatures. The pest damages Bermuda grass hayfields and pastures throughout the Southeast U.S. and is regularly seen throughout the Coastal Plain region up to Macon.

“(The pest) kills the top two leaves of the plant. Once it damages the top, we don’t get any more upright growth out of the plant and it really hurts our yield. We can see as much as 80% yield loss if we’re not careful,” Baxter said. “It’ll look like you’ve frosted the top of your hayfield because of the dead stems at the top.”

For up to date information about Georgia’s climate conditions, see UGA agricultural climatologist Pam Knox's blog, Climate and Agriculture in the Southeast.

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