Late-planted crops are at increased risk from insects that normally pose a lower threat, said Wayne Bailey, University of Missouri Extension entomologist.
Black cutworms continue to threaten fields in north-central and northeastern Missouri. “Due to small seedling size and the large size of black cutworm larvae, damage can be rapid and severe,” Bailey said. “With the relatively high price of corn, treatment is justified if 1 to 2 percent or more of plants are cut by this pest.”
Due to multiple moth flights, cutting in northeastern Missouri continues on seedling corn. Producers should scout fields for signs of leaf damage or cutting until corn reaches the five-leaf stage.
Brown stink bugs also pose a threat to corn this year due to planting delays and the small size of corn plants, Bailey said.
“Stink bugs are present in high numbers this spring and have the potential to substantially damage seedling corn,” he said.
Adult stink bugs overwinter in non-crop plants bordering fields. In spring, they move out of these areas to feed on field crops. Damage usually shows up first on field edges before moving inward several corn rows, Bailey said.
To protect crops, scout field edges for stink bugs hiding in corn plant whorls and feeding on seedling stems, Bailey said. Spray field borders and corn rows along field edges to keep the stink bug from migrating into fields.
“Most producers don't catch them until it's too late,” he said. “At that time, you already have twisted plants and feeding damage. If you have a woody area nearby, or alfalfa, I would definitely be scouting. You might spray grassy borders as a preventive if you've had stink bugs before.”
Stink bug damage comes from piercing-sucking mouthparts, which the bugs use to remove sap from host plants, Bailey said.
“Damaged plants either wilt and die completely, sometimes shooting up a weedy tiller, or if they survive, often appear twisted and distorted,” he said. “As the corn plants grow in size, stink bug damage is often seen as a line of holes surrounded by a yellow edge running across the surface of the corn leaf.”
Soybean farmers with early-planted fields should watch for bean leaf beetles. “Wet weather has limited soybean planting and allowed high numbers of beetles to accumulate in seedling soybean fields,” Bailey said.
“High numbers of adult beetles require insecticide application to reduce populations below the economic threshold,” he said.
For seedling soybean, the economic threshold is five or more beetles per row foot, or one or more plants destroyed per row foot, Bailey said.
Adult beetles feed on plant leaves; larvae feed on soybean plant roots. Economic damage from bean leaf beetles is more common later in the season when second-generation beetles feed on soybean pods. However, numbers this year are higher than usual in seedling fields due to limited soybean planting.
Other pests to be aware of this season are corn earworm, white grubs, wireworms and Japanese beetles.