Friday, February 23, 2024

Pests On The Move

Something old, something new – insect problems may not be what first comes to mind.

⋅ BY AMANDA HUBER ⋅

Two species of the rootworm complex can be found in peanuts in Georgia. For many years, it was the Southern corn rootworm or larval stage of the 12-spotted cucumber beetle that could be found in more moist soils.

At the 2023 Cotton/Peanut Field Day, University of Georgia peanut entomologist Mark Abney shows a collection of Southern corn rootworm-damaged peanut pods (left) compared with undamaged ones.

University of Georgia Extension entomologist Mark Abney says if the soils are not wet, this native species won’t survive. However, it’s the non-native banded cucumber beetle that producers are seeing in their fields more often, and soil moisture does not appear to be as much of a factor.

“Banded cucumber beetle seems to be able to survive in drier soils,” Abney says. “We have seen a difference in Southern corn rootworm in irrigated and non-irrigated fields, but we didn’t see that  difference for banded cucumber beetle between irrigated and non-irrigated fields.”

Rootworm Spread

Just as the banded cucumber beetle is adapted to drier soils, it is also spreading and becoming more abundant in sandier, more well-drained soils.

“Southern corn rootworm was almost always found in heavy-textured soils with good moisture,” he says. “But now, we are seeing banded cucumber beetle in fields where, historically, you did not have rootworm infestations.”

Unfortunately, granular chlorpyrifos, an insecticide no longer available since the U.S. Environmental Protection Agency revoked all tolerances to it, was the best option for managing rootworm. Abney says they are working on potential alternative control measures but would also like to hear from farmers if they find the pest in fields for the first time.

Because the immature stage of the beetle lives entirely below ground, Abney says to dig plants to examine pods for damage and check the soil for larvae. Often, the pest is not found until peanuts are dug and tiny, pinhole damage is found on the pods.

Scouting Your Fields Is Essential

The cool, wet start to 2023 wouldn’t seem to be the type of weather that would lead to lesser cornstalk borers, but by the first week of June, they were reaching threshold in fields across Georgia.

“Then it started to rain,” Abney says. “There are a lot of folks with the mistaken idea that rain kills lesser cornstalk borer, but it does not. Rain does make it harder to find the insect in the field because it washes away silk tubes and reduces the chances that infested plants will show wilt symptoms.”

Cool weather means it will take longer for lesser cornstalk borer eggs to hatch and for larvae to become adults, and this generally gives beneficial insects more time to do their work. At some point in Georgia, it will be hot and dry enough for an outbreak. The only way to know if a lesser cornstalk borer infestation is building and reaching threshold is to scout fields. PG


Burrower Bugs Found In Virginia Peanuts

Photo courtesy of Steve Brown, bugwood.org.

Another insect pest formerly controlled with chlorpyrifos is burrower bug. Without this control method, producers are left using more conventional methods in an attempt to stave off this subterranean pest.

Burrower bugs were found this past season on the Virginia Tech Tidewater Agricultural Research and Education Center farm and identified by the Virginia Tech Insect Identification Laboratory.

Virginia Tech entomology graduate student Elijah Hoar says damage has been minimal in the Suffolk, Virginia, area, but it is something to keep in mind.

“Some producers have gone back to using a moldboard plow and completely turning over the soil,” he says, “And some producers have been planting earlier hoping for a thicker hull development earlier in the season.

Burrower bugs can cause a wide range of damage to peanut kernels, which is not visible until after the peanuts are harvested and shelled.

“Damage caused by the peanut burrower bugs looks similar to stink bug damage,” he says. “This is only seen when peanuts are shelled and the skin is removed at buying points by graders. The insect does not leave an indicator of damage on the shell of the peanut.”

Hoar says, “Peanut burrower bug is more of an issue in hot, dry years, and they are just as sporadic as Southern corn rootworm.”

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