Agronomic Crop Insects – September 3, 2010

Joanne Whalen, Extension IPM Specialist;

Continue to sample fields on a weekly basis for defoliators including earworm, webworms and all armyworm species. Economic levels of defoliators continue to be found causing damage.

As of this date, economic levels of recently hatched corn earworm larvae have been reported in soybean fields in all 3 Delaware counties. Although Monday’s moth catch showed a slight decrease due to the cooler temperatures over the weekend, these new larvae are a result of the high trap catches over the previous 7 day period. With the recent return of warmer weather, fields will still need to be scouted for corn earworm larvae, especially double crop soybeans. When selecting an insecticide, be sure to check all labels for the days from last application to harvest as well as other restrictions.

There are also a number of defoliators still present in full season soybeans including bean leaf beetles, grasshoppers, and isolated areas of green cloverworms. The pest complex varies from field to field. The threshold should be reduced if a mixed population is present. As a reminder, both bean leaf beetles and grasshoppers can also feed on pods.

As of yesterday, we have documented the presence of brown marmorated stink bugs (BMSB) in a soybean field near Harrington, DE. This would be the first occurrence in Kent County. We did find it for the first time earlier in the season on soybeans in New Castle County. Although this stinkbug has caused significant damage to fruit and vegetable crops throughout the Mid-Atlantic region, little is known about the damage it causes in soybeans, as well as what the treatment threshold would be. The following links provide good information on the biology and identification of this stinkbug species:;

Soybean Loopers in Soybeans
We starting to hear reports of “loopers” in some fields and at least in one case the defoliation was significant. As indicated in past newsletters, soybeans loopers are a migratory pest and in the states to our south resistance to pyrethroids has been documented. We also have cabbage loopers (also a migratory insect pest) present in some fields which are generally controlled by pyrethroids. Identification can be difficult because although there is a “black footed” phase of the soybean looper there is also a “ green phase” that can be confused with cabbage loopers. One characteristic that might help is the presence of microspines on soybean loopers that are not present on cabbage loopers; however, you will need high magnification to see the microspines.

The following is information from Ames Herbert in Virginia’s recent Ag Pest Advisory that provides information about what is happening with soybean loopers in Virginia:

Looper infestations over most of the state– Soybean loopers are now being reported in soybean fields across much of the eastern side of the state. In past years they were mostly confined to southeastern counties. This infestation has broken all the records in terms of intensity (as many as 100+/15 sweeps in some fields) and geography (now being reported from Middle Peninsula and Northern Neck counties). This must be due to the persistent hot, dry weather, and the high percentage of fields previously treated with insecticides. Loopers are easy to identify but there is some confusion about their color. Soybean loopers have both a green and a black color phase We are seeing both color phases in our samples. There may be some cabbage loopers (a completely different species) mixed in, but we have not verified this. There are no exact thresholds for loopers in soybean so treatment should be based on the amount of leaf feeding in relation to the size of the total canopy. But, a very loose rule of thumb could be that 20 or more per 15 sweep net sweeps may constitute a threat. Fewer than that, especially in tall, full canopy fields probably does not constitute a threat. Some fields are getting close to maturity with pods and leaves beginning to yellow. Loopers are not a threat to those fields. Pyrethroids should not be figured into a looper treatment decision. They are less than effective.”

Be sure to look at the following link for pictures of both color phases of this insect.

Small Grains
With the increase in no-till wheat acreage as well as our typical rotation of wheat following corn, it will be important to consider a number of insect pests that can present problems. The following article provides a good review of insect pests that pose a threat to wheat in the fall including aphids, the wheat curl mite, Hessian fly and fall armyworm. ( In addition to the insect pests listed in this article, true armyworms have been a pest in the past, as well as slugs, if we have a wet fall.

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