Black cutworm (BCW) and true armyworm (TAW) moths have been making their way into Ontario over the last few weeks. Black cutworm in particular have been arriving since mid April in southwestern Ontario, with trap counts increasing weekly. Shout out to our new northern Ontario trap participants at the New Liskeard, Thunder Bay and Emo Research Stations for monitoring BCW traps up there after last years significant cutworm infestations. It helps us keep an eye out for risk in that region. Thankfully, no moths have been captured in that region yet. To see more details on moth catches, visit the dashboard and maps of the Great Lakes and Maritimes Pest Monitoring Network.
Growing degree day models for black cutworm indicate that eggs that were laid from those moths that arrived in southwestern Ontario in mid April will have hatched and small larvae may begin feeding on leaves of host crops. Larger larvae that cut the plants aren’t expected for a few more weeks, though warmer temps forecasted for next week will speed up their development.
Fields at risk include those with low lying, pre-plant weeds or cover crops (e.g. mouse-eared chickweed, mustards, volunteer wheat or oats, lamb’s-quarters), no-till fields with green vegetation, late spring plowed fields or late planted fields. Scouting is recommended in already emerging corn fields and other high risk crops like sugar beets that are up. Plan to scout fields that were weedy or had green cover crops present last month, once the main crops do come up. Bt corn containing Cry 1F or Vip3A proteins are protected against black cutworm. Insecticide seed treatments also provide effective control.
Look for leaf-feeding (pinholes) by young climbing larvae as the first sign of damage. Also look for wilting plants, foliage-feeding or for plants being cut off at the ground. Dig around damaged plants and search through the soil, as cutworms like to hide in the soil during the day. Note the size of the cutworms found.
For corn, if more than 10% of plants show leaf feeding, treating with a foliar insecticide will give nearly 100% control. Larvae larger than 2.5 cm are almost done feeding and are not effectively controlled by insecticide. Once corn reaches the five-leaf stage and begins to produce roots at the base of the plant, the risk has passed.
More information on black cutworm biology, scouting and management options can be found on Ontario CropIPM and black cutworm control products can be found on the Crop Protection Hub.
As for true armyworm, its too early to tell what our risk is like for this pest. Our scouts are monitoring for this pest and cereal leaf beetle in 29 YEN sites this year. We will keep you updated on if and when we start to see larvae at these sites.