Watch for Black Cutworm Injury

Black cutworm larva and damage (Photo credit: Jocelyn Smith, UGRC)
Black cutworm larva and damage (Photo credit: Jocelyn Smith, UGRC)

Some US states to our south have been reporting high numbers of black cutworm moths in their pheromone traps and are starting to see some black cutworm injury in newly emerging corn fields.  These moths are carried into Ontario via storm fronts. Once they arrive the adult moths look for weedy patches in fields to lay their eggs on.  The larvae hatch about a week later and start to feed at night on corn leaves before migrating below the soil surface to cut plants at or below the soil line.

Fields at risk include those with pre-plant weeds (eg. chickweed, mustards, volunteer wheat, lamb’s-quarters, velvetleaf etc), cover crops or crop residue.  No-till fields, late spring plowed fields with annual weeds or fields planted into sod or legume forages are most prone.  Fields near Lake Erie tend to have more frequent infestations.

Scout those fields that have not been planted with a Bt hybrid containing Cry1F or Vip3A .  Foliar insecticide treatments can provide effective control if applied at threshold and before larvae are larger than 2.5 cm.  Inspect 20 plants in five areas of the field once or twice per week from VE to V5.  Look for pinholes on the leaves, or wilted or cut plants.  Dig the ground surrounding the injured plant to find the larvae.  Fields with a history of infestations should be planted with Bt hybrids that effectively protect the crop from this pest.

Foliar threshold: Control is warranted if 10% of plants in the V1 toV4 stage have damaged leaves/pinholes or 3% of more plants are cut and larvae are smaller than 2.5 cm.  Insecticides are less effective on larvae larger than 2.5 cm.  Risk of damage has passed once the corn reaches the V5 stage.

Foliar insecticide options can be found here.

More information on black cutworm can be found in the Guide to Early Season Field Crop Pests.