As corn begins to emerge, growers should be alert to the potential for damage from early season insects such as cutworms, wireworms, white grubs or other insects. A key distinction to be aware of is that soil insects such as white grubs and wireworms can only be controlled with planting time treatments; cutworms and other caterpillars potentially can be controlled postemergence.
Wireworms and white grubs are most often associated with fields that have been in pasture or CRP where the grasses were allowed to grow for more than one year. It is rare to see these problems in continuous corn, but exceptions happen. Since wireworms and white grubs feed underground and cutworms feed on or below the soil surface, scout for plant damage and then dig in soil around the plant to identify the insect causing the damage.
Cutworms and other insects may hinder emerging corn plants this spring, even if seed was treated with insecticide or Bt corn hybrids were used. High populations of insects can overwhelm the protection method, regardless of whether it was an insecticide applied at planting (liquid, granular, or seed treatment) or a Bt corn hybrid.
Cutworms can cause serious damage to corn in the first couple of weeks after emergence so it is important to scout fields early for damage. Several species of cutworms attack corn. The severity and the area affected will vary greatly, depending on species involved, previous crop history, and weather conditions.
The black cutworm does not overwinter in Nebraska, and infestations depend on moths moving up in spring winds from the south. They are most commonly found in the eastern one-fourth of the state. Fields with winter annual weeds or abundant crop residue are more attractive to the egg-laying black cutworm moths in the spring.
Black cutworm moths may also be attracted to dense cover crop vegetation to lay eggs. Black cutworm larvae are light gray to nearly black in color with an overall greasy appearance, and reach 1.5 inch long at maturity. When viewed through a hand lens the skin has a rough pebbly texture. The head has two black stripes and there is a pale band along the top of the body. A key characteristic is that on the top of each abdominal segment there are two sets of paired spots which are unequal in size.
After hatching, cutworm larvae may begin feeding on the cover crop and later move to a cash crop when the cover crop is terminated. In 2016, Dunbar et al. captured significantly higher numbers of black cutworm moths in rye cover crop plots from late April through early May in Iowa. A couple of weeks later corn plants were assessed for cutworm damage, but no significant cutworm damage was observed.
Such observations reinforce the need to scout fields even when adults have been observed. True armyworm has a similar behavior to black cutworm in that it targets areas of dense vegetation for egg laying.
Several other cutworm species (dingy, claybacked, army, and Sandhills cutworms) overwinter as partly grown caterpillars and can be found more widely in Nebraska. Remember that early detection of a problem is essential because most cutting occurs within seven days of plant emergence.
Nebraska corn fields need to be scouted immediately
