Stink bugs have become a significant and increasingly common threat to corn production across many growing regions. These insects, named for the unpleasant odor they release when disturbed, are not just a nuisance; they are direct pests that feed on developing kernels. The damage they inflict can lead to substantial economic losses for farmers, primarily through dockage at elevators due to damaged kernels and reduced overall grain quality. Understanding the lifecycle of these pests and the specific ways they harm corn is the first step in implementing an effective management strategy.
Identifying the Primary Culprits
While several species can impact corn, the Brown Marmorated Stink Bug (BMSB) and the Green Stink Bug are most frequently responsible for economic damage in corn fields. The BMSB, an invasive species originally from Asia, has spread rapidly and is particularly aggressive. These bugs are characterized by their shield-shaped bodies and mottled brown or green coloration. They use piercing-sucking mouthparts, similar to a straw, to penetrate the corn ear and feed on the silks, kernels, and cob tissue. This feeding behavior is the direct cause of the quality issues that result in financial losses.
The Mechanism of Kernel Damage
Feeding Sites and Visual Symptoms
The damage occurs when stink bugs pierce the ear husk to reach the developing kernels. Their saliva contains digestive enzymes that break down the kernel tissue, turning it into a soft, discolored mass. Visually, the damage appears as yellowish or white scars on the kernels, often creating a "cat-facing" deformity where the kernel fails to develop fully on one side. In severe infestations, the entire ear may appear shriveled or discolored, and the kernels may be aborted entirely, leading to significant yield loss.
Impact on Grain Quality and Market Value
Beyond the visual damage, stink bug feeding compromises the grain's integrity and test weight. Damaged kernels are lightweight and often fail to meet the standards required for food-grade corn, forcing them into lower-value channels such as ethanol production or animal feed. The presence of damaged kernels can also lead to storage issues, as the broken tissue is more susceptible to fungal growth and mold. At the elevator, the dockage applied for stink bug damage can be substantial, making pest monitoring throughout the season a critical financial practice.
Lifecycle and Timing of Infestation
Stink bugs are prolific flyers and move into corn fields from surrounding vegetation, such as wooded edges, soybean fields, and conservation areas. They are most damaging during the milk and dough stages of corn development, when the kernels are soft and filled with milky fluid. As the season progresses and kernels harden, the damage potential decreases, though late-season infestations can still affect test weight and harvestability. Scouting is essential because populations can fluctuate, and a field that is safe one week may be overrun the next.
Monitoring and Scouting Strategies Effective management begins with walking the fields and checking for the presence of bugs and the resulting ear damage. Use a sweep net to sample the perimeter of the field, as stink bugs often enter from the edges. When inspecting the ears, look for the characteristic cat-facing and the presence of the insects themselves, which may be hiding under the husk or within the whorl. Thresholds for treatment vary by region and growth stage, so consulting with your local extension service is vital to determine the precise economic injury level for your area. Integrated Pest Management Approaches
Effective management begins with walking the fields and checking for the presence of bugs and the resulting ear damage. Use a sweep net to sample the perimeter of the field, as stink bugs often enter from the edges. When inspecting the ears, look for the characteristic cat-facing and the presence of the insects themselves, which may be hiding under the husk or within the whorl. Thresholds for treatment vary by region and growth stage, so consulting with your local extension service is vital to determine the precise economic injury level for your area.
Cultural and Chemical Control
Managing stink bugs requires an integrated approach that combines cultural practices with targeted insecticide applications. Planting dates can be adjusted to avoid peak stink bug migration periods if possible. When chemical control becomes necessary, choosing the right insecticide is crucial. Products must have good coverage to penetrate the husk and contact the feeding bugs. Applying insecticides at the correct timing, often during tasseling or early silking, maximizes efficacy. Always follow label instructions carefully to prevent resistance and ensure the safety of beneficial insects that help control other pests.
