Editor’s note: The following was written by Kelly Estes, coordinator of the Illinois Cooperative Agriculture Pest Survey, for the University Extension Pest Management Bulletin.
Impressive moth flights have not only kept the Illinois insect monitoring network cooperators busy, but neighboring states are reporting lots of black cutworm and true armyworm moth activity as well. The current forecast and planting progress has raised questions about the potential for these pests in the coming weeks.
With the assistance of University of Illinois Extension educators, producers and industry volunteers, nearly 60 trap sites have been established across Illinois. Captures of both black cutworm and true armyworm have been common across the state.
Several counties have reported significant flights (nine or more moths caught over a two-day period). In fact, several counties had repeated significant flights.
Black cutworm moths are strong migratory insects with northward flights commonly observed from Gulf States into the Midwest from March through May. Moths are attracted to fields heavily infested with weeds, such as chickweed, shepherd’s purse, peppergrass and yellow rocket.
Late tillage and planting tends to increase the susceptibility of fields to black cutworm infestations.
Cutting of corn plants begins when larvae reach the fourth instar, with a single cutworm cutting an average of three to four plants during its larval development.
Cutting tends to occur most often during nights or on dark overcast days. Fields at greatest risk to cutting and economic damage are in the 1- to 4-leaf stage of plant development.
An early warning sign of potential economic damage includes small pinhole feeding injury in leaves (caused by the first three instars). Producers are encouraged to look for early signs of leaf feeding as a potential indicator of cutting, rather than waiting for cutting to take place.
Cutting of plants earlier than these projected cutting dates is possible — localized intense flights may have occurred and were not picked up by our volunteers.
A nominal threshold of 3 percent cutting of plants has traditionally been used as a point at which growers should consider a rescue treatment.
Not all Bt hybrids offer adequate protection against black cutworm damage. Growers should consult the Bt trait table prepared by Chris DiFonzo at Michigan State University to determine the level of protection provided by their chosen Bt hybrid: https://tinyurl.com/mn46jvm.
Switching our focus to true armyworm, this insect has also been very active this spring. Illinois has seen steady flights across the state with numbers slowing down only within the last two weeks.