Agronomic Crop Insects

Joanne Whalen, Extension IPM Specialist;

Alfalfa and Grass Hay Crops
Be sure to watch for corn earworm, fall armyworm, beet armyworms as well as other defoliators. The following link provides a list of materials labeled for defoliators in these crops: . Before treatment, be sure to check all labels for the rate; comments on control under high populations and size of larvae; days to harvest as well as forage/silage restrictions, as well as other use restrictions. As far as fall armyworm, we have just gotten reports of grass hay fields being damaged by armyworms so fields should be watched closely after cutting for armyworm damage to the re-growth. Larvae must be small at the time of treatment to achieve effective control.

Corn Earworm (CEW) Alert
The potential for corn earworm pressure in soybeans is high statewide. Trap catches remain high throughout the state and moths can be found laying eggs in fields. With the continued high trap catches throughout the state, be sure to check all fields for earworms.

Consultants in Delaware as well as on the eastern shore of Maryland are reporting economic levels as well as in some cases extremely high levels of corn earworms in both full season and double crop fields. Remember, corn earworms can feed on the foliage and blossoms as well as the pods. The only way to know if you have an economic level will be to scout. Although there is no threshold for corn earworm feeding on flowers or leaves, data from North Carolina has indicated that feeding on flowers can result in reduced yields by delaying pod set. We also know that during the last CEW outbreak year, high levels of earworms completely stripped fields of all the leaves and blossoms. Therefore, it is critical that all fields be scouted for corn earworm. When looking at foliage feeding by corn earworm, you will need to use defoliation as well as the presence of worms to make a decision (again – there is no worm threshold available for leaf and/or blossom feeding). Once pods are present, the best approach to making a decision on what threshold to use for corn earworm is to access the Corn Earworm Calculator developed at Virginia Tech ( which estimates a threshold based on the actual treatment cost and bushel value you enter.

During the past 3 seasons as well as this season, states to our south, including Virginia, have reported controls failures with pyrethroids for CEW control in soybeans. Up until 2009, poor control in our area has been the result of treating too late, treating large worms or using too low of a rate. If you use a pyrethroid for earworm control, be sure to use the highest labeled rate. In addition to the pyrethoids, Steward, Lorsban or Larvin could also be considered, especially if armyworms are in the mix. In some fields, fall armyworm and beet armyworm can also be found.

For more information on what is occurring in Virginia, you will want to look at the Virginina Ag Pest Advisory ( which is generally updated by Friday each week.