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Louisiana soybeans hit with corn earworm

Corn earworm infestation for many Louisiana soybean fields. Recommendations provided.

On Thursday morning (July 7), Roger Leonard, LSU AgCenter Professor of Entomology and J. Hamilton Regents Chair in Cotton Production, provided the following update on an outbreak of corn earworm in Louisiana soybean fields. It reads:

“Many fields in Louisiana are experiencing outbreak levels of corn earworm (CEW). This is not the case in every field, but my calls for the last couple of days have been from all except the southern-most soybean production areas across the state.

“CEW numbers are far exceeding the action threshold of eight larvae per 25 sweeps.In many cases, these numbers are one to two insects per sweep.These levels are not common in Louisiana across such a widespread area.

“The most attractive and ‘high risk’ fields are those in full flowering stages (R2-R5) because the adults are attracted to flowering to oviposit their eggs. Fields beyond this point are less preferred, but still should be sampled to confirm infestation levels.

“Again, every field is not infested, but those found to be infested at these heavy levels should be treated with insecticides immediately.

“Unfortunately, many soybean fields in Louisiana are not being scouted on a regular schedule and it is easy to miss these infestations. I think these insects have been building during the last 7-10 days. Outbreak levels such as these will remove all flowers and small pods on plants so it is important to scout fields for this problem. 
“When CEW numbers are at levels equal to, or just over, the action threshold, the standard pyrethroids at high labeled rates or the pre-mixes (Leverage 360, Endigo, or Brigadier) will provide acceptable control.

“Our pyrethroid susceptibility monitoring indicates relatively high levels of resistance and suggests that under these populations those products used alone will not provide effective control. However, at outbreak levels of 2x the action threshold or higher, I am recommending co-applying 0.5 lb of Acephate to ensure effective control.

“There are other CEW-active products available that are efficacious, but they are expensive and only control caterpillar pests. These include Belt, Tracer, and Steward. These will be effective, but should be used at the upper rates as well. Of these, Belt will likely be the most active and provide the longest residual.

“Be sure to re-sample three to five days post-treatment to measure performance. If populations persist, a second application may be warranted in a few instances.

“The key is to scout and only treat those fields that are infested. Automatic applications will only serve to flare other pests.”

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