To date, this has been one for the records in terms of corn earworm pressure in soybeans. Many of our fields have been treated, although most are still in the flowering/late flowering stage. We do not have thresholds for flowering beans but know that high numbers of worms can do too much damage by eating all the flowers which can result in delayed maturity. What’s next for these fields? Will earworms recycle to present another threat to podding fields? My guess is, yes, at least some percentage of fields may need to be retreated. The decision to retreat should be made based not on rumor, seeing spray rigs running in the neighbor’s field, or conversations at the diner, but based on knowledge that thresholds have been met. Growers cannot afford to make unnecessary sprays, especially with low yield potential and having already paid for one application. And, if a pyrethroid was used the first time we would strongly recommend that these second applications be non-pyrethroids. If you have treated with Karate, Baythroid, Endigo, Birgade, Bifenthrin, Tombstone, Sniper, Mustang Max, Hero, Proaxis, or Leverage—you have treated with a pyrethroid. In our field trials we are having good success controlling worms with relatively low rates of these non-pyrethroids (e.g., Steward at 4.6 oz and Larvin at 10 oz). But even at these rates, the cost is more than the pyrethroids.

Many full-season soybean crops on the Eastern Shore of Virginia were sprayed for insect pests this week. In many cases, these sprays were needed as pest numbers of spider mites, corn earworms, green cloverworms and other caterpillar pests were high. In the fields that I insected, I saw a lot of green cloverworm, corn earworm, yellowstriped armyworm, and some beet armyworms. I did not see soybean loopers, which often are hard to kill. Beet armyworms have also shown resistance to pyrethroids in past trials on the Eastern Shore. A number of different insecticides were applied. Some growers sprayed Steward to combat the complex of caterpillars; whereas some others sprayed Orthene and a pyrethroid such as Warrior to combat the mix of pests. Other growers sprayed a generic Lorsban 4E, which provided efficacy against the spider mites as well as the caterpillar pests including beet armyworms. Let’s hope our growers do not have to spray again, as these sprays were applied early in the crop, and we’ve still probably yet to see the major flight of corn earworms that attack the pods.

Corn earworm has moved into soybean fields across much of Virginia. This is earlier than normal and most are faced with the decision to treat (or nor) flowering stage beans. Infestation levels vary a lot from field to field from almost no worms in lush canopy fields, to drought stressed open canopy fields with as many as 25+ per 15 sweeps. Although we have decent thresholds for foliage feeding and pod feeding, there is little guidance as to the impact of flower feeding by corn earworms. Several years ago researchers in North Carolina (Eckel et al. 1992) concluded that flower feeding contributed to yield reductions by delaying pod set, but no exact thresholds were developed. Without good guidelines as to how many can be tolerated, we are suggesting that low to moderate numbers (6 or less medium plus large worms/15 sweeps) could be safe, especially if beans are growing well with good soil moisture. More than that may represent a threat. Again, just a ‘grab’.
We are also getting a lot of calls from folks finding live worms after pyrethroid sprays, in cotton, peanut and soybean fields. Most are using either Karate Z or Baythroid XL and the ‘misses’ are about equal among the products. The most obvious cases are where there were very high numbers of worms so the survivors are still quite noticeable. We visited one field that had been sprayed 24 hours earlier and found an average of about 4 to 8 worms/15 sweeps. Since it was still not forming pods, I suggested that it not be retreated, yet.
Of course, any field that has been treated will be very susceptible to any subsequent infestations, as beneficial insects would have been mostly eliminated so be sure to begin re-scouting 7 days after the last application. If another treatment is needed, strongly consider a non-pyrethroid.
We are also seeing a mix of worm species including yellow striped armyworms, green cloverworms, and maybe some tobacco budworms. Corn earworm is still the primary species, so I would direct the spray program to those.

Annually, we conduct a survey to estimate corn earworm infestation levels in field corn in late July. Earworms develop in corn, then move to other crops such as soybean, cotton, and peanut in August. We determined the number of corn earworms found in 50 ears of corn from 5 randomly selected corn fields in each of 24 counties, totaling 5,800 ears and 116 fields sampled. Statewide, 42% of ears were infested with earworms. This is up from 36% in 2009. Regional averages were 12% infested in Northern, 28% in the Northern Neck, 39% in Mid-Eastern, 58% in the Southeast, and 46% on the Eastern Shore. See the attachment with results from each county and many more details. From the survey, it looks like the areas of greatest risk to heavy infestations of earworms are the southeastern ‘cotton/peanut’ counties, and the Eastern Shore. However, as large as this effort is, it is not a complete picture. We always recommend scouting individual fields to determine exactly what is happening in terms of corn earworm as well as other pests and crop problems. We will continue posting moth catch numbers and other information regarding the 2010 insect pest situation.
Additional information: cew-survey-table10-2-docx