The 2024 planting season is fast approaching, and Missouri corn growers should consider being on the lookout for early corn pests throughout the state. Growers can also sign up for the Pest Monitoring Network (https://ipm.missouri.edu/pestMonitoring/) and receive alerts when insect captures exceed certain threshold levels. Here we highlight some of the early-season insect pests of corn, scouting methods, and management recommendations.
Black cutworm
The black cutworm, Agrotis ipsilon (Rottemburg) is a migratory pest in Missouri. Early infestations are likely from migrating moths from the Gulf Coast or Mexico. In corn, black cutworm larvae can cause damage to corn seedlings by cutting plants at or below the soil surface (dragging the plants into their holes to feed during the day), resulting in stand losses. Moth traps using sex pheromones can be used to monitor adult moths arriving in the area. The University of Missouri field specialists are monitoring black cutworm migration in several locations throughout the state. So far in 2024, moths have been captured in seven counties. Moth captures in a pheromone trap do not indicate that treatment is necessary, but indicate that fields should be scouted. Scouting for larvae is the only way to accurately determine if management is warranted. It is important to begin scouting when corn emerges by examining 25 corn plants at each of the 10 widely distributed areas in a field, every 7-10 days until corn reaches the V4-V5 growth stage. More information on black cutworm management can be found here (https://extension.missouri.edu/publications/g7112). Additionally, black cutworm larvae predominantly feed during night hours and return to subsurface refuges during daylight hours. Insecticide applications should be applied to fields either at dusk or dawn to increase the likelihood of insecticide efficacy.
True armyworm
The true armyworm Pseuduletia unipuncta (Haworth), overwinters as larvae in Missouri. Migrant adult moths also arrive in Missouri in early April. While armyworms can have two to three generations per year in the state, the larvae of the first generation in May and June usually cause the most feeding damage. True armyworms feed on a variety of grasses including corn. In corn fields, examine 20 plants in each of at least five locations within a field. True armyworm larvae are not active during the day. Scouting should be performed during the early morning or late afternoon hours. Treatment is recommended when 25 percent or more of the seedling corn plants are damaged and larvae are still present. So far in 2024, true armyworm moths have been captured in six counties. While this information cannot be used to warrant management, it can be used to guide scouting efforts.
2024 true armyworm trap locations.
Brown stink bug
Brown stink bugs (Euschistus spp.) are the primary stink bug pest species of corn in Missouri. Stink bugs have piercing-sucking mouth parts and early in the season, they feed at the base of the seedling corn plants. Feeding injury during the early vegetative stages of corn (V1-V6) can result in plants being stunted, irregular growth, or killed. It can also result in the production of yield-robbing tillers from the base of damaged plants. Scouting is essential to determining stink bug damage.
Keys to look for when scouting:
- Stunted corn plants or thinned corn stands
- Elongated feeding holes on seeding corn leaves. This is caused by stylet insertion when leaves are still curled within the whorl.
- Brown stink bugs present in the field
Management
1 stink bug per 4 plants (25% infested plants) before VT
Pyrethroids are typically not as efficacious on brown stink bugs when compared to other common stink bug species in Missouri.
Image of black cutworm courtesy of Maurien Trabbold via Shutterstock