Now isn’t the time we normally think about widespread armyworm damage in corn. However, it is the time when migrating moths are moving into the state and may cause damage to scattered seedling corn fields when/if field conditions are favorable. This spring migration is unpredictable in terms of incidence and severity. States to the south have reported scattered problems or high blacklight trap catches, which is typical for this time of the year. However, their damage (or lack of damage) does not always give us a good indication what will happen in Wisconsin. It does, however, give us an early warning and reminds us to do some spot checking in fields for damage. Scouting each field for armyworm damage is certainly the best approach but, admittedly, not always practical. By understanding their habits we can target our efforts to those fields most likely to have damage. Females prefer to lay eggs on grasses and especially, in field situations where there is a dense weed (or crop) canopy.

 

Corn

             Spot-check no-till corn planted into grass cover crops. These fields may be so strongly attractive to egg laying that bordering conventionally tilled fields show little armyworm damage. In similar fashion, corn no-tilled into alfalfa can be an attractive egg laying site as can early season grassy weed growth. This isn’t to suggest that clean tilled fields without early season weed problems will not have armyworm damage. My intention is, because of limited time, to point out those fields most likely to have damage. Treat corn only when armyworms are less than ¾ inch long and you have two or more larvae on 25% of the plants or if there is an average of 1 armyworm on 75% of the corn plants.

 

Small Grains

 

While you are out scouting, don’t forget to check spring and fall planted small grains. Check lodged areas first because moths prefer dense stands of vegetation to lay eggs. Shake several plants vigorously then check the soil surface for larvae.  If you find armyworms in these areas it would be advisable to check the rest of the field for larvae and/or damage. When larval populations reach 3/square foot an insecticide is justified.