Many Pyrethroid Failures on Bollworm in Mississippi Soybeans

Angus Catchot, Extension Entomologist
By Angus Catchot, Extension Entomologist July 22, 2011 16:55

As of now, I have had numerous reports of pyrethroid failures in soybeans targeting bollworms.  Nearly everyone with soybeans at R1-R4 has bollworms at some level in the delta region of the state.

So what is going on?

Mississippi has traditionally planted mainly group IV soybeans early and we have missed the bollworm flights in previous years.  As grain prices have increased we are planting more wheat beans and more maturity group V soybeans later to manage around harvest of corn.  We have essentially exposed a large portion of the crop to a time of the year where the highest bollworm numbers are present.

Consequently we are having to treat more acres.  In 2006, MS treated only 1800 acres for bollworms, 2007 we treated 125,000 acres, 2008 we treated 250,000, 2009 and 2010 we treated around 450,000 acres for bollworms.  In past years bollworms were extremely easy to control in soybeans and even the low rates of pyrethroids were providing excellent control.

In the last couple of years we have been seeing declining efficacy with pyrethroids in all crops on bollworms.  From 2006-2008, I could count on both hands the total number of complaints about control and could trace most of them back to thick canopies or too low of rates etc.  Last year we had numerous field control issues in soybeans and in cotton.  Ryan Jackson with USDA-ARS made numerous collections across the delta last year after field control problems and documented various levels of tolerance to the pyrethroids using topical assays.

We had some fields where bollworms were highly resistant and some fields only moderately resistant, and still other fields where they were susceptible meaning the most likely problem was coverage in rank beans.  We also documented higher levels than normal of tobacco budworms in soybeans last year which are highly resistant to pyrethroids contributing to the control problems.

This year I have literally had too many calls to count of unsatisfactory control of bollworms in soybeans.  This has been across a wide group of pyrethroids at the highest labeled rates in many cases.  There are still a few folks who are reporting adequate control with straight pyrethroids but failures have been too numerous to expect this on many acres.  I have identified worms from several fields and so far they have all been bollworms but several consultants this week have reported flushing budworms moths in the last couple of days in soybeans.  This is going to come down to how much risk you want to take.  You basically have 3 options.

  • Third choice:  The cheapest option is go with straight pyrethroids at the highest labeled rates, but the chance of control problems are high.
  • Second choice: Highest labeled rate of pyrethroid plus 0.5 lb acephate.  This combination will improve the control of the pyrethroid but will not completely remove the risk of a failure.  I have gotten several good reports behind this mix but also several reports where this did not help.
  • First choice:  spend the money and apply Belt at 2-3 oz or Steward at 1:16 – 1:20 depending on pressure.  These options will cost more but will greatly reduce the risk of failure.  Keep in mind that when pyrethroid tolerance begins to creep in, even a small problem with coverage or not using the right rates will magnify the control problems exponentially.
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Angus Catchot, Extension Entomologist
By Angus Catchot, Extension Entomologist July 22, 2011 16:55
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  1. Justin July 23, 22:54

    Angus, please comment on the necessity of adding a “sticker” to your sprays. For me it’s the difference in what’s working and what’s “not working”.

    Reply to this comment
    • Angus Catchot, Extension Entomologist Author July 24, 17:09

      The subject of adjuvants can be complicated with insecticides. There are some pest in combination with certain insecticides where it is the difference in control and no control sometimes. A great example is the use of an MSO at .5-1.0% with the neonics for aphid control in cotton. For other pest it has been less clear such as plant bugs and some leps. At the very least they likely do improve canopy penetration especially on very hot days. On caterpillar pest such as bollworm in soybean, if the reason for poor control is truely resistance adjuvants will likely make little difference.

      Reply to this comment
  2. Jon July 25, 15:07

    What is the thresh hold count for bollworms? Should we take out the drift reduction tips in order to get smaller droplet size to help penetrate canopy closure? Thanks!

    Reply to this comment
    • Angus Catchot, Extension Entomologist Author July 25, 15:23

      Threshold is 8-9/25 sweeps or 3 per row foot on a drop cloth. We also say 1/2 inch long before counting them, however, with the control issues we are having we may be better off targeting smaller worms. Absolutely take out low drift tips. It makes huge difference with contact insecticides like pyrethroids.

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