Black Cutworm & Armyworm Moth Captures Show a Big Increase

Black cutworm (BCW) and armyworm (AW) moths captured in the IPM traps at the UK Research and Education Center in Princeton, KY show a substantial increase for the trap week ending Friday, April 10.

In the case of BCW (Figure 1), 37 moths  were captured when about 8 would be expected.

Figure 1. Black cutworm moth. (Photo: Doug Johnson, UK)

Figure 1. Black cutworm moth. (Photo: Doug Johnson, UK)

For armyworm (Figure 2), 541 moths  were captured when 119 would be average at this time.

Figure 2. Armyworm moth. (Photo: Doug Johnson, UK)

Figure 2. Armyworm moth. (Photo: Doug Johnson, UK)

Captures for both of these pests are significantly greater than their rolling 5-year averages. In addition, if the armyworm counts continue to increase at this rate, the population will approach the outbreak levels seen in 2006 and 2008. These are years when known pest problems either caused loss or required extra insecticidal control. See the Insect Trap Count Graphs on the UK IPM webpage.

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 fields and laying eggs, which will eventually hatch into caterpillars (the damaging stage). So, this is an early warning. Depending upon the temperatures over the next 2 weeks or so, egg lay and maturation will begin.  This is followed by hatch of 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 there is not 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 Bt 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. For more information, see Insecticide Recommendations For Corn – 2015, ENT-16. 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 KY Integrated Crop Manual for Field Crops – Corn Section 1, pp.4-5 in IPM-2).


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. For more information, see the IPM corn manual listed above and KY Integrated Crop Manual for Small Grains (IPM-4). Generally, armyworms will feed on leaf edges from the outside in, leaving a very distinctive damage pattern. Because feeding is only on leaves, plants can tolerate a considerable amount of damage before a rescue treatment is needed. In corn, control is recommended when armyworms are an average of ½ to ¾ inch 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 to ¾ inch long and there are 16 worms per 4 square feet. Multiple samples are needed for each field to determine the extent of infestation. Spot treatments can often provide effective control of localized infestations, such as those occurring at field-margins.


By Doug Johnson, Extension Entomologist


Posted in Grains