Black cutworm can cause stand losses and in severe enough situations can require replant.
Black cutworm can cause stand losses and in severe enough situations can require replant.

It’s prime time for black cutworms (BCW), and they could be inching their way into fields right now. Cutting yields—and plants—is what these pests do best.

“Black cutworms can cause a reduction of plant population,” said Michael Gray, professor and Extension entomologist, Department of Crop Sciences, University of Illinois. “If a stand is reduced enough, in some cases, a farmer may need to consider  replanting. This can be very costly.”

As their name suggests, cutworm species chew through the stems of corn plants and target seedlings between one and four leaf stages. BCW attack corn plants early in the season and can result in substantial stand, and ultimately, yield loss. Many corn fields are primed for exposure to damage right now.

Facts about BCW:

  • BCW overwinter in the Gulf Coast States and migrate to northern states in the early spring months. Flights typically start in March and are biggest in April and May.
  • Average BCW may cut 3-4 corn plants.
  • Eggs are typically laid in clusters and larvae hatch in 5-10 days.
  • There are 3-4 generations of BCW per year in most Corn Belt states.
  • Moths prefer to lay eggs in fields with established weeds or crop residue.
  • You are more likely to have BCW in corn after soybeans  or after winter wheat.
  • Fields with reduced tillage, late tillage and planting, no-till, next to permanent vegetation, annual weed infestations or with soybean residue are at higher risk of BCW infestation.

“Don’t assume ‘If I planted a BT hybrid—I don’t need to worry about this pest,’” suggests Gray. “Not all BT hybrids offer the same level of protection. If it just offers suppression, scout more diligently.”

Corn is most susceptible when it’s 15” or shorter, but can still suffer damage in later stages. The first sign of infestation may be pinholes in leaves because when BCW are young, they do not cut the plant at the base. However, as they grow they will be able to cut plants completely.

Plants may be able to recover from BCW injury. However, if the cut is made below the growing point, the plant will not recover. As corn reaches later stages, BCW can tunnel into the plant and hollow out the stalk through the growing point.

Corn seedling cut by a black cutworm. Photo credit: University of Illinois.

When scouting, be sure to diligently check low spots in fields. Take special caution when chickweed, shepherd’s purse, peppergrass and mustard weeds are present. BCW favor these weeds to lay their eggs.

How can fields be protected?

Plan to scout all fields at least once per week for three to four weeks after corn emergence. In each field check at least five locations and 50 plants. Keep a tally of how many plants have leaf feeding (pinholes), cutting, wilting or missing plants. If a plant has damage, dig around the plant to try to find the BCW larvae. They burrow in the ground to seek moisture—this could be 3” to 4” in dry areas. Be sure to give special attention to late planted or weedy fields. A post-emergence rescue spray should be considered when 3% or more of the plants are cut and larvae are still present, according to the University of Illinois.