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23
Aug
2012
Soybean Loopers Arrive
Author: Scott Stewart, IPM Extension Specialist 3 Comments

I’ve had the first report of treatment level infestations of soybean loopers in West Tennessee, and I’ve also seen an upsurge in larval numbers this past week.  I am not surprised as infestations have been migrating northward through Mississippi and Arkansas the past few weeks.

 

Loopers have two pair of prolegs.  This separates them from other caterpillars that may also be present.  I previously wrote and article about distinguishing loopers and green cloverworms, another common defoliator that is typically less damaging and easier to control.  Loopers do not feed on pods.  They are foliage feeders. It is important to not let defoliation exceed 25% prior to R6.  The impact of defoliation on yield will be very minor after R7.  Looper populations may be composed of both the soybean looper and cabbage looper, but soybean loopers often compose the majority of the population during late season.  Unfortunately, they are more difficult to control with insecticides.  Below are some tips for managing infestations of soybean loopers.

  1. Treatment is recommended anytime before R6 if defolation exceeds 20-25% or if looper populations exceed an average of 19 larvae per 25 sweeps.  Small larvae cause little defolaition, so concentrate your scouting on larvae bigger than 1/2 inch in length.
  2. Do NOT use a pyrethroid insecticide to control loopers.  Pyrethroid insecticides typically provide no better than 0-50% control, and populations sometimes rebound to even higher levels following treatment.  Indeed, you are more likely to have problems with soybean loopers if a pyrethroid insecticide was used within the last several weeks.
  3. Use one of the recommended insecticides below.  They all should provide excellent control of loopers and other defoliating caterpillars that occur in Tennessee.  Unfortunately, you will have to tank mix with another insecticide if stink bugs are also present in treatable numbers.

 

Recommended Insecticide for Control of Soybean Loopers:

  • Intrepid (4-6 oz/acre) – Be prepared for a slow death.  Some larvae will persist for 5-6 days after treatment, but little feeding will occur after the first few days.
  • Steward (6-8 oz/acre)
  • Tracer (1.5 – 2 oz/acre)
  • Belt SC (2 oz/acre) - A relatively new product that appears to provide more residual than the other choices.  Thus, it would be my choice if loopers get an early start. It is a little more expensive.

Can I Cut Rates?

Well it is legal, although companies will not stand behind lower than labeled use rates if a failure occurs.  I would not consider cutting rates unless loopers arrived late (R6 or later).  At this time, you only need to protect plants from excessive defoliation for another 14-21 days, and the plants are getting progressively less sensitive to defoliation.  I’ve done several tests looking at reduced rates of Intrepid at 2-3 oz/acre in combination with a pyrethroid insecticide or Belt at 1 - 1.5 oz/acre.  I’ve seen good control in these tests, but you should expect less residual activity.  Using a slightly lower rates of the above products in combination with a pyrethroid insecticide is something to consider if stink bugs are also in the mix (which looks to be a likely scenario this year).  However, you do so at your risk, especially if looper populations are well above the treatment threshold.

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3 Responses to Soybean Loopers Arrive

  1. Chris Harrell says:

    Would you mind specifying the locality of where treatments are being made?? West TN is a pretty large geographical area.

    Just finished spraying milo for worms, corn earworm, armyworm, and web worms, concentrating on the developing heads. First planted milo is beginning to show color in the top of the heads.

    So far, scouting has not showed anything but low numbers of 3 corner alfalfa leaf hoppers, double crop beans. First crop beans are fast approaching where the only thing we are watching for would be any late pod feeding pests.

    This would be Hardin County, specifically around Savannah.

    • Scott Stewart, IPM Extension Specialist says:

      Chris

      I’ve had reports of above-threshold infestations of loopers from Haywood and Dyer county. We are above threshold in two fields in Jackson … only some wheat beans so far. It is always amazing how one patch will need treated while the other does not. My counterpart in Arkansas indicates they have fields above threshold across the river in Mississippi county. So I think there is potential for problems throughout West TN. What can I say? They are getting started, but like most insects, field to field variation is huge. It is shaping up to be a “looper year”. That means heads up … but don’t assume you will have to treat. Late soybeans will be at greater risk. Stink bugs are the only pests showing up in treatable numbers in early maturing fields, but many fields are hitting threshold after R5.

      We just rated milo tests today … lots of corn earworms but few sorghum webworms or fall armyworms. The pyrethroids performed OK (80-90% control) but the pressure was so high that we were still finding 2-4 larvae per 10 heads after treatment.

  2. Chris Harrell says:

    Thanks for the more specific information.

    We got lucky on the corn earworm, in that they were on the low end of what we had for infestation. Armyworm was our high population bug, so the high rate of generic Warrior did a good job on cleaning up the fields.

    Wheat beans have a lot of potential, “here”, so we are watching them like a hawk for any infestations, plus hoping for more rain.