For the last week of August 2010, about 35% of corn earworm moths survived 24 hours of exposure to 5 micrograms of cypermethrin (a pyrethroid) in our vial tests. Moths were collected from pheromone traps in Suffolk, VA. We have evaluated 2,598 vials so far this season. Please see the attached line graph to see results for the entire season. Additional information: cew-cypermethrin-ppt

Mean nightly corn earworm moth captures for 20-26 August 2010 were as follows: Petersburg (34), Prince George-Wells (10), Prince George-Lipchak (50), Southampton (68), Suffolk (18), Sussex (18), Essex (5), Northumberland (16), Richmond County (28). Please see the attached table for more information. Additional information: blacklight-table-10-doc

Seven of nine reporting locations had their highest 2010 captures of corn earworm moths this week (13-19 August). Please see the attached table for more details. Additional information: blacklight-table-10-doc

As predicted, we are in the midst of a second flurry of corn earworm and tobacco budworm moth activity. Some black light traps are catching even higher numbers than during the first flight. Moths are flushing from peanut, cotton and soybean fields. Each crop is presenting a different scenario in terms of risk to infestation and potential crop damage. I can almost guarantee that peanut and soybean fields will be re-infested with worms, and there is a very good possibility that the infestation will be a mix of both species.

PEANUTS almost never suffer economically from worm feeding, but growers will likely not tolerate the worms and tank mix some insecticide with a planned fungicide application.

SOYBEANS are a different story. This next influx of worms will coincide with pod development and fill. Many fields that have been drought stressed are getting some rain and plants are reflowering which makes them highly attractive to moths. I think pod thresholds will be met or exceeded in many fields and many will need to be re-sprayed. Most of these fields have already been treated, but in my opinion, and in the opinion of other soybean entomologists, no product offers more than about 7 days residual activity so any field treated more than 7 days ago will be completely vulnerable to worms. Another piece of the puzzle is the continued high pyrethroid resistance levels of corn earworm. As of this week, we have tested 1,903 moths and survivorship has climbed back to over 40% (see the attached figure). One sample this week reached 56%. Is this resistance level increasing because many of these moths are from the worms that ‘escaped’ the earlier pyrethroid sprays? Seems logical. The best control will need to incorporate a non-pyrethroid (Larvin, Lannate, Steward, Tracer, Belt). Another tank mix that seems to be working well where ever it is being used (the Delta states, Tennessee, North Carolina) is to add 6 oz of Orthene to a full pyrethroid rate.

COTTON may be the least attractive and least susceptible to this next influx of worms. The hot, dry weather has pushed cotton to cutout with many bolls already too tough to be damaged by worms. Much of the crop will be ready for defoliation within the next 3 weeks or so.
Without some top growth of new tender flowers, squares or small bolls, young worms will not be able to establish. And even if this top growth does become infested, it represents a very small proportion of the total yield, which makes controlling worms (the cost) a tough decision.
Additional information: cew-cypermethrin-19-aug-2010-ppt

Dr. Herbert mentioned in his 29 July 2010 advisory that we are continuing to monitor for pyrethroid resistance in corn earworm. We have now tested over 1,500 moths and are averaging 28% survival in the 5 ug cypermethrin vials (click ‘More’ to see the data). This is now the third consecutive year that local corn earworm populations are demonstrating high levels of pyrethroid resistance. As Dr. Herbert said in his advisory, proceed with caution and consider non-pyrethroids especially in peanut or soybean fields with a lot of worms. Additional information: cew-cypermethrin-2010-pdf

In general, nightly black light trap captures of corn earworm moths remained high this week. Please see the attached pdf for more details. Additional information: blacklight-table-10-pdf

We have confirmed that tobacco budworm is in both soybean and peanut fields. We have attached a table with the percentages of each, corn earworm (CEW)/tobacco budworm (TBW), from 8 fields in Virginia and northeast North Carolina. Note that the IDs were based on the differences in jaw construction in the two species (mandibular identification) which means the jaws of each worm (240 total) had to be dissected and inspected under high magnification. Most collections came from fields that had been recently treated by the grower with either Baythroid XL or Karate Z. We also included the day post treatment that the worms were collected. With the exception of collections from two untreated fields, these worms represent pyrethroid ‘escapes’. Unfortunately, we do not have pre-treatment samples so do not know what the species ratio was prior to application. ‘Escapes’ ranged from 4 to 86% TBW. Were these ‘selected for’ by the pyrethroid sprays, as TBW is known to be harder to kill with pyrethroids? That would be our best guess. In the future, knowing the ratio of CEW/TBW could be critical to achieving good control by guiding the insecticide choice. If TBWs are known to be in the mix, it might tip the scale in favor of using the more effective, but more costly, non-pyrethroids. In soybeans, that means Steward, Larvin, or Tracer. In peanuts, Steward or Tracer. Soon there may be some new options. Our field plot research is showing a lot of promise for Bayer CropScience’s Belt insecticide, Dupont’s Coragen insecticide, and a few others. When will they be available and what will they cost? Good questions.

Additional information: larval-id-2-herbert-malone-2010-doc