kudzu bug treatment threshold Alabama soybeans

Kudzu bugs transforming insect control picture of soybeans

Kudzu bugs are forcing a change in pest control for soybean producers. Profitable production is no longer possible without scouting at proper intervals. Excessive spraying could eliminate beneficial insects.

While it’s not the end of the world for producers, the presence of the kudzu bug on Alabama soybeans represents a new departure for growers in terms of pest management, says one expert.

To put it another way, with the advent of this pest, soybean insect control has grown more challenging and complex, he says.

Ron Smith, an Alabama Cooperative Extension System crops consultant and Auburn University professor emeritus of entomology, says that if there is one take-home message for soybean producers, it’s that they will no longer produce soybeans profitably without pest scouting at regular intervals.

Other critical lessons must be learned, too, he adds.

“In addition to regular scouting for kudzu bugs and other pests, soybean growers also should learn to recognize these bugs in both their immature and mature cycles,” Smith says.

This lesson closely relates to another critical one: Using knowledge of the pests’ growth cycles to apply sprays at the optimal time and, equally important, to avoid excessive spraying.

“It’s critical for these producers to know when to spray, and just as important for them to know when not to spray,” he says.

“If growers are monitoring and doing everything right, they will probably spot kudzu bugs all season long — which conceivably could lead some to spray  five, six or seven times. We can’t spend our budget spraying every time we see a kudzu bug in the field.”

Even so, while limiting the numbers of spraying applications to two or three a season should be the desired goal, this will be no easy task, says Alabama Extension entomologist Tim Reed.

“Fortunately for Alabama growers, Extension entomologists on the frontline of control efforts in South Carolina and Georgia soybean fields already have treatment recommendations in place,” Reed says. “But growers should be aware that these recommendations are still evolving and that there is still a lot more to be learned about kudzu bugs.”

Southeastern entomologists currently advise growers to consider spraying when monitoring reveals five bugs for each seedling and before the plants exceed a foot tall.

After that, spraying applications should be considered after monitoring reveals 10 bugs per plant on plants larger than two feet.

For best accuracy, entomologists recommend sampling for the bugs at least 50 feet from the edge of the field.

“This recommendation is based on the fact that adult kudzu bugs have an extended migration period — six to eight weeks — and colonize field edges first,” Reed says. “So, sampling along the edges may lead some growers into to spraying too soon — in other words, before migration is over.”

If there is any good news in all of this, it’s that the bugs also have a long life cycle — six to eight weeks in length —or a couple of generations, Smith says.

“What this means is that if we can time our applications perfectly, we could get by with as few as two or three applications a season, depending on the crop’s planting dates,” he says, stressing that the earlier the planting, the more likely the need for multiple sprayings.

“If we can get by with only a couple of sprays, we’ve done it perfectly, he adds.”

Smith and Reed urge growers to be mindful of a major risk associated with excessive spraying: The likelihood that spraying, while removing kudzu bugs, will also eliminate beneficial species that play a critical role in keeping other virulent soybean pests at bay.  These pests include soybean loopers and velvetbean caterpillars.

“When you treat for a pest like kudzu bug, you’re increasing the likelihood that a high percentage of caterpillars will survive and defoliate your plants, adding an addition $10 an acre in control costs, especially in the case of soybean loopers,”Reed says.

While it’s true that kudzu bugs lack the potential to wipe out the soybean crop, Smith says complacency about the bugs can prove to be a dangerous mindset in many cases, adding that he has already inspected several fields that could suffer a complete wipeout if treatment is not begun soon.

TAGS: Management
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