Stink bug overview and identification
The brown stink bug, Euschistus servus, and southern green stink bug, Nezara viridula, can be damaging pests of field corn in South Carolina. While it has a high potential for injury, it is considered a sporadic pest because it does not occur at damaging levels in every field every year. Due to the sporadic nature of this pest, it is important to understand potential risk factors for infestation and have a plan in place before the growing season to be ready to address it efficiently and effectively if damaging populations occur.
Stink bugs are shield-shaped insects, which are similar in shape and size across species. As the name suggests, the brown stink bug is dark brown in color. There is a beneficial stink bug species that may be confused with brown stink bugs, but can be distinguished by the presence of pointed and sharp shoulders (i.e. pronotum), which the pest brown stink bug does not have. Nymphal brown stink bugs are light green in color and have a distinctive brown patch on their abdomen. Southern green stink bugs are slightly larger than brown stink bugs and green in color. The nymph of southern green stink bugs have a series of pink, white, and black spots on their abdomen, which can easily distinguish them from other species. Other species that can occur in corn but are either far less common or not pests of corn in South Carolina are the brown marmorated stink bug, green stink bug, and rice stink bug.
Left: adult brown stink bug. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org. Right: fourth instar brown stink bug nymph. Image credit: Herb Pilcher, USDA Agricultural Research Service, Bugwood.org
Left: Adult southern green stink bug; note the presence of tachinid fly eggs. Right: fourth instar southern green stink bug nymph. Image credits: Russ Ottens, University of Georgia, Bugwood.org.
Injury to field corn
Field corn is susceptible to injury during three key stages of field corn development: 1) emergence (VE) – six-leaf stage (V6), 2) two weeks prior to tasselling (VT) during the earliest stages of ear development, and 3) the first two reproductive stages of development (R1 and R2). During the early vegetative stages (i.e. VE-V6), stink bugs feed directly on the growth point of young plants, which can lead to stunted plants, tillers, leaf holes, deformities, or plant death in severe cases. Prior to tasseling and pollen shed, feeding on the early stages of ear development leads to a characteristically “banana-shaped” ear, which limits overall yield potential and can expose the ear to secondary pests and pathogens. It is important to note that during these stages, the ear is not yet visible, but stink bugs can use their straw-like mouthparts to penetrate into it. Beyond pollination, direct feeding on kernels has limited potential to directly impact yield but can introduce grain quality issues in the form of fungi and mycotoxin contamination if bugs are at a high enough density.
Early vegetative injury from stink bug feeding. Left: plants stunted with multiple tillers. Right: Severely stunted plants. Image credit: Tim Bryant, Clemson University.
Banana-shaped ears as a result of stink bug feeding during late vegetative stages prior to tasseling. Image credit: Tim Bryant, Clemson University.
Discolored kernels and fungal growth as a result of stink bug feeding during early reproductive stages of corn development. Image credit: Tim Bryant, Clemson University.
Population dynamics and management
Identifying at-risk fields can help save time in deciding when and where to scout for stink bugs. During early vegetative stages, fields that are planted into heavy cover crop residue can potentially be at higher risk for large populations and injury. Proper seed slot closure can be affected by this heavy cover and expose more sensitive portions of the plant to feeding, increasing injury potential. Fields that were planted with soybeans in the previous season can also be at a higher risk for early-season infestations. Later in the season, the interface of wheat and corn is at high risk for stink bug infestations. Wheat is an excellent early-season host for stink bugs, which can easily move into nearby corn during wheat harvest. Wheat harvest often coincides with the later vegetative stages of corn development, which are susceptible to stink bug injury.
For early vegetative infestations, insecticidal seed treatments, which are applied almost universally to commercial corn seed, can provide some protection from early season injury. Generally, fields with a history of stink bug pressure or at risk of injury from soil pests may benefit from increased seed treatment rates. Additionally, foliar insecticides can effectively manage stink bugs throughout the season, but it is critical to scout and only apply an insecticide at the economic threshold level for the given growth stage. The economic threshold is 1 bug per 10 plants from V1 to V6, 1 per 4 plants from V12-VT, and 1 per 2 plants at R1 and R2. The two most important considerations for applying an insecticide are achieving good coverage and timing the application properly. Ensuring canopy penetration is especially critical during the later stages of corn development. Bifenthrin is generally the most effective material to target brown stink bugs specifically. Applying an insecticide only at the economic threshold level will also preserve naturally occurring biological control agents in the field that broad-spectrum insecticides would otherwise kill.
For more detailed biology and management information on brown stink bugs in field corn, see this Land-Grant Press article.
