Coming Soon - Armyworm and Black Cutworm Feeding

Tracey Baute - Field Crop Entomologist/OMAFRA Ridgetown
16 May 2008

The blacklight trap set up here at Ridgetown Campus has started to capture adult true armyworm moths. This means that eggs are being deposited and larvae should begin feeding within two weeks time. Wheat fields and corn fields should be scouted no later than the week of May 26th to stay ahead of any outbreaks. True armyworms tend to feed at night, however they can feed during they day when it is cool and overcast. Generally, fields most at risk are those having had a cover crop such as rye or had poor grassy weed control. In conventional-till cornfields, damage usually occurs first in the border rows, whereas infestations may develop throughout no-till corn following small grains or grass.

Reports from other states also indicate that black cutworms moths have been flying around for the last month or so (our blacklight trap was not functioning until earlier this week so we did not capture these flights). Most at risk are fields that had winter annual or perennial weeds like chickweed, volunteer wheat, rye cover crop or any green vegetation left on the soil surface this spring. No till fields with heavy crop residue can also be at risk. Corn growers along Lake Erie have a history of cutworm issues but other areas could also be impacted. Newly hatched cutworms will feed on weeds in the field until the corn crop comes up. Unfortunately the earlier the larvae start on the weeds, the bigger they are when they move over to the corn plants. These larger larvae are more difficult to control in their larger size. Fields treated with Poncho seed treatment or planted with Herculex Bt corn are protected from the younger larvae though they are still at risk of damage by larger larvae. Look for wilting plants, foliage feeding or for plants being cut off at the ground. If 5 to 10% of plants show leaf feeding injury, rescue foliar treatments at that time are very effective. Once corn reaches the 5-leaf stage and begins to produce roots at the base of the plant, the risk has passed.