First Bollworms Showing up in Mississippi Soybeans

This week we are starting to get some calls of the first soybean fields reaching threshold for bollworms.  Bollworms (Corn Earworms) can be extremely devastating to soybeans because they feed directly on all fruiting structures.  Many folks are also reporting flushing very high numbers of bollworms moths this week in soybeans which likely means this will be more widespread in the next 7 – 10 days.  Watch for this one very close, they can sneak up on you quickly.  Bollworms are preferentially attracted to wide row open canopy soybeans that are flowering.  This does not mean you will not find them in other fields but they usually show up first in the open canopy fields.  Also, pay close attention to any field that had a pyrethroid applied to it recently.  It is not uncommon to find many more bollworms in a field where the beneficial insects have been removed.  Pyrethroids have been very effective in controlling this insect in the past in Mississippi; however, we had a few cases of pyrethroid tolerance last year and the addition of 0.5 lb of acephate improved control.  This is not something we see every year, but last year we documented tobacco budworms in many fields across the delta mixed in with the bollworms. One field we sampled was 67 percent tobacco budworms.  Tobacco budworms are resistant to pyrethroids.  If you are flushing budworm moths this year it is a possibility that they may be present also.  Products that will control both are Belt and Steward but they are more costly.  Also, in beans that have thick foliage I would strongly consider using 5 gallons by air.  Louisiana is currently experiencing extremely high numbers of bollworms in some of their fields as well.  Usually, what happens in Louisiana hits us about 10-14 days later.  The following is an alert that Dr. Roger Leonard put out a couple of days ago for Louisiana that contains some good information regarding bollworms in soybeans.

Louisiana Bollworm in Soybean Alert by Dr. Roger Leonard: 

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 8 larvae (>1/2 in) per 25 sweeps.   In many cases, these numbers are 1-2 insects per sweep.  These levels are not common in Louisiana across such a widespread area.   The most attractive and “High Risk” fields are those which are in the 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 which are 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 3-5 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. 

Bollworms from Soybean, by Roger Leonard, Click to Enlarge