Soybean:  As I feared, corn earworms are making their presence felt again in soybean.  Again, the heavy action is mostly concentrated in the Mississippi River bottoms.  Following last week’s high moth catches up and down the River, there have been numerous reports of many moths in fields.  Again, use a treatment threshold of 9 larvae per 25 sweeps (36/100 sweeps).  Good control has been reported from the suggested insecticide recommendations (below).  As we get later is the season, there may be more benefit to using Belt as it will spare beneficial insects and should provide residual control of loopers that MIGHT show up in the next few weeks.  Soybean loopers and looper moths are starting to be reported more commonly.  Steward will probably not provide the same potential residual, at least at the rates below, but it also costs less.  A word of caution – do not jump the gun treating for corn earworms in soybean.  Basing an application on the presence of moths may force a follow-up treatment that could have been avoided.

Insecticide recommendations for corn earworm in soybean

1) Pyrethroid insecticide + 0.5 lb of Acephate/Orthene

2) Steward at 6-7 oz/acre (1:20 is 6.4 oz per acre)

3) Belt SC at 2 oz per acre (1:64).

A straight pyrethroid should only be used when populations are only a little above the treatment threshold.  There have been some questions about using a reduced rate of Belt and adding a pyrethroid as a tank mix partner.  I’ve had the same thought when other, non-caterpillar pests are present in treatable numbers.  Using 1.5 oz of Belt should be a good rate in a tank mix that includes a pyrethroid insecticide.  I would not go any lower than this in a tank mix.  Keep in mind that this reduced rate is not listed on the label, so you use it at your own risk.  Also, you will potentially lose some residual control if using lower rates.

Cotton:  Be prepared to make additional insecticide applications to late-maturing cotton fields for bollworms.  The Bt technologies have performed well this year.  However, high pressure and the relatively late maturity of many fields in the river bottoms will force our hand in many situations. Sporadic but continuing bollworm pressure is also occurring in other areas.  I’ve included some data from a test this year in Jackson (below).  These data make two points:  1) Bt cottons are providing good protection, and 2) some bollworm larvae slipped through.  In this case, Bollgard II provided excellent protection but treatment reduced boll damage for the WideStrike variety.  It’s a numbers game, and Bt technologies will require treatment for bollworm in some circumstances.

Evaluation of Bollworm/Tobacco Budworm Control (Madison Co. TN,  8/17/11)

On Bt cotton, I still suggest sticking with a high rate of a synthetic pyrethroid insecticide.  Adding 0.5 lb of acephate should be considered if plant bugs are also present.  This will also enhance control of bollworms.  Refer to last week’s article about terminating insecticide applications.  Many fields in the state are now “safe” from bollworm, plant bugs and stink bugs as they have passed NAWF5 +350 DD60s.  However, I’ve had several calls about heavy plant bug infestations in later maturing cotton.  Fields that had had 4 or more nodes above white flower this week will need protected from plant bugs, stink bugs and bollworms through the end of the month.