Black Cutworm & Armyworm Moth Captures Show a Big Increase

Doug Johnson, Extension Entomologist, University of Kentucky

Fig. 1 Black cutworm moth.

Black cutworm (BCW) and armyworm (AW) moths captured in the IPM traps at the UK-REC in Princeton, KY show a substantial increase for the trap week ending Friday, April 10th. In the case of BCW, 37 moths were captured when about 8 would be expected. For armyworm, 541 moths were captured when 119 would be average at this time. Captures for both of these pests are significantly greater than their rolling five- year averages. In addition, if the armyworm counts continue to increase at this rate, the population will approach the outbreak levels seen in 2006 & 2008. These are years when known pest problems either caused loss or required extra insecticidal control. See the Insect Trap Graphs on the UK-IPM webpages.


Remember that traps capture the adult moths of these pests and the adults are not the damaging stage. Adults are responsible for pest movement into your fields and laying the eggs which will eventually hatch into caterpillars which are the damaging stage. So, this is an early warning. Depending upon the temperatures over the next two weeks or so, egg lay and maturation will begin followed by hatch of the caterpillars that will begin feeding on any food source available.

Black Cutworm –At this time of year the important grain crop host of BCW is corn and we don’t have much of that planted yet. Because there is little corn planted, good early weed control will be particularly useful in preventing cutworm damage. If plants that provide egg lay sites and food for BCW are well controlled, that will aid in reducing the BCW populations in fields as corn emerges. Additionally, many corn products that contain the “B.t.” traits Cry1ab and vip3A2a0 (viptera), provide “very good control” and those containing Cry1F provide “good” control. Not all corn products are labeled for BCW control so check the label of the products that you have chosen to be sure. (See Ent-16 - Insecticide Recommendations for corn – 2015. This publication also contains listed products for rescue treatment if an infestation in detected.
Rescue treatments are based on field sampling to find the active cutworms before significant damage is inflicted. (See IPM-2 - KY Integrated Crop Manual for Field Crops – Corn Section 1, pp.4-5).

Fig. 2 Armyworm moth.

Armyworm- Armyworm is a general pest of most grass crops. At this time of year the two most important of these are corn and small grains. (See Corn manual as listed above and KY. IPM-4 Integrated Crop Manual for Small Grains). Generally, armyworms will feed on the leaf edges from the outside in, leaving a very distinctive damage pattern. Because they are feeding only on the leaves, the plants can tolerate a considerable amount of damage before a rescue treatment is needed. In corn, control is recommended when armyworms are on average between ½- ¾” long and the entire field averages 35% infested plants or 50% or more defoliation is seen on damaged plants. In small grains, consider control if armyworms are between ½-¾”- long and there are 16 worms per four square feet. Multiple samples are needed for each field to determine the extent of the infestation. Spot treatments can often provide effective control of localized infestations like field-margins.