Category: Field Crop IPM

Spodoptera frugiperda or fall armyworm is a common pest of numerous crops in South Carolina. Overwintering sites in North America include south Florida, Texas, Mexico, and the Caribbean. Each year, the insect migrates through much of the U.S., including South Carolina where infestations are generally found starting in June, with populations often increasing later in the season. We were surprised to find last week whorl infestations of fall armyworm so early in the growing season. The female moths lay eggs in masses on corn leaves, and larvae feed on leaves, creating rows of holes. This type of injury occasionally leads to yield losses when population densities are high in a field. Fall armyworm larvae has an inverted Y mark on its head (Figure 1) the distinguish it from related species. More information on the identification and management of fall armyworm can be found in our Land-Grant Press article.

Figure 1: Inverted Y mark on Spodoptera frugiperda larvae. Image credit: Steve L. Brown, University of Georgia, Bugwood.org.

Larvae of fall armyworm were found in our corn field trial located in Blacksville, South Carolina, last Thursday (May 8, 2025). Larvae were feeding on non Bt corn leaves when plants were at the V3 growth stage (Figure 2), with a typical aggregated pattern of several plants in a row infested, followed by uninfested plants. The trial has plots with Bt corn which were not infested with fall armyworm.

Figure 2: Fall-armyworm larvae feeding on corn leaf, Blacksville, SC. Image credit: Author.

It’s the time of year to be on the lookout for stink bugs in corn in South Carolina. Several species can cause damage, with the brown stink bug, Euschistus servus, and southern green stink bug, Nezara viridula, being the most common. While damage at the seedling stage can occur, the most common injury occurs when stink bugs feed from V14-VT. Which leads to crooked or banana shaped ears. We outline here information on stink bug biology, damage, and management.

Overview and identification

Stink bugs are shield-shaped insects, which have a similar appearance across species. As the name suggests, the brown stink bug is dark brown in color. There is a beneficial stink bug species called spined soldier bug that may be confused with brown stink bugs, but is distinguished by the presence of pointed and sharp shoulders (i.e. pronotum), which are absent on the brown stink bug. Immature or nymphal brown stink bugs are light green in color with a 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 has a series of pink, white, and black spots on their abdomen, which can be used to distinguish them from other species. Other species such as the brown marmorated stink bug, green stink bug, and rice stink bug can be common in South Carolina, but are not common pests of corn.

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.

Damage to 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, feeding leads to a characteristically crooked or “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 mouthparts to penetrate into the plant and find the developing ear to feed on. After pollination, 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, with 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. 

Sampling and management

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. As wheat matures and dries down, 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 and this scouting guide for stink bugs in southeastern corn.

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.

Contributing Author: Dr. Francis Reay-Jones

More than 80% of field corn grown in the U.S. has been genetically engineered to express one or more insecticidal toxins from Bacillus thuringiensis, called Bt toxins. Bt corn was first commercialized in the U.S. in 1996, expressing a single Bt toxin targeting the European corn borer. Newer Bt corn hybrids express two or more Bt toxins, which has increased the number of target pests to include the corn earworm and the fall armyworm. Benefits of planting Bt corn can include protecting yield from insect damage, reducing the need to use insecticide, and improved grain quality. However, such benefits can be impacted by the development of resistance in target insects.

Dr. Francis Reay-Jones is continuing this year to evaluate the efficacy of Bt traits and the impact Bt toxins have on the life cycle of the corn earworm, with implications on resistance evolution. “We have been conducting field efficacy trials with a range of Bt traits since 2009. Since then, we have seen some traits become less effective over time because corn earworm has developed resistance. We saw in particular a shift in 2015 when resistance to some of the Cry toxins expressed in Bt corn became more widespread not just in South Carolina, but across the southeastern U.S.” Although the corn earworm is generally not a significant economic pest of field corn, the same species is a serious pest in cotton, where it is known as bollworm. Because Bt cotton expresses the same or similar toxins as Bt corn, selection for resistance in Bt corn is likely driving resistance issues to Bt cotton. “Planting a non-Bt refuge is the only tool we have to manage resistance. Preventing resistance development in Bt corn is crucial so that the insect does not cause more damage to Bt cotton later in the season, where the corn earworm (or bollworm) is a major economic pest.”

While resistance in corn earworm is widespread to most Cry toxins used in Bt corn and Bt cotton, one toxin, called Vip3A, remains highly effective. Trials in South Carolina continued this year to evaluate Bt corn hybrids expressing Vip3A. Examination of hundreds of corn ears in 2023 showed that these hybrids remain highly effective, with no ear injury found due to corn earworm feeding. In corn, this toxin is expressed in Trecepta, Optimum Leptra, and Agrisure Viptera products. While Vip3A remains effective, reports of unexpected injury in recent years in the mid-south underline the need for continued resistance monitoring. Vip3A toxins are also expressed in new Bt cotton varieties, and planting of non-Bt refuge in corn is crucial, since only a single Bt toxin is currently available with very good activity for this key pest.

On Thursday, July 27, a corn production field day was held at Clemson University’s Edisto Research and Education Center in Blackville, SC. The field day was well attended by growers and other stakeholders to learn about the latest research and recommendations for corn agronomy, disease and nematode management, insect management, and soil fertility management.

Dr. Michael Plumblee, Clemson’s corn and soybean extension specialist, organized the field day in addition to providing updates on his on-going work with double cropping corn and soybean, corn variety trials, and corn fungicide efficacies. Double cropping corn and soybeans is a new strategy that Dr. Plumblee and his graduate student, Bennett Harrelson, are exploring as a potential mechanism for growers to increase profitability in the long South Carolina growing season. In this system, corn is harvested early and soybeans are immediately planted. Dr. Plumblee’s research seeks to identify best management practices for this system including planting date, harvest date, soybean variety, and nematode management.

Dr. John Mueller, a field crop pathologist and nematologist, provided updates on several nematacides that are commonly used by growers, Counter 20G and Velum. On-going trials conducted by Dr. Mueller will help determine which of these products provides effective control for growers. Dr. Mueller also spoke about corn fungicide trials that are on-going in collaboration with Dr. Plumblee. Dr. Mueller says the good news for growers this season is that it has been a relatively light disease year so far.

Dr. Mike Marshall, a field crop weed specialist, provided an update on a number of different pre and post emergent herbicide programs that could be used by growers in the field. There are many different herbicide programs that growers can utilize, and continued efforts to test the efficacy of these programs allows growers to be informed and not use herbicides which may not provide good levels of control.

Dr. Francis Reay-Jones, a field crop entomologist, provided an update on the state of insect pest management in corn. Dr. Reay-Jones emphasized the importance of planting non-Bt refuge corn each year to delay the continued development of Bt resistance in corn earworm populations. While corn earworm is generally not an economic pest of corn, it is a major pest of cotton, where it is known as bollworm. Since cotton expresses many of the same Bt toxins that corn does, resistance management in corn continues to be a critical strategy to prevent further issues in managing the insect in cotton. Tim Bryant, provided an update of the state of stink bugs in field corn. Stink bugs are the most important economic insect pest of corn in the Southeast, but it is also a sporadic pest, so scouting is critical for growers to effectively manage it.

Finally, Dr. Bhupinder Farmaha provided an update on soil fertility practices for corn. Soil samples should be taken in the field and sent to the Clemson Agricultural Service Laboratory to provide a full break down of the nutrient contents of the soil in a field, allowing growers to amend the soil in a targeted and effective way. Dr. Farmaha also stressed the diminishing returns seen from soil amendments beyond a certain amount, emphasizing the importance of these soil tests.

All of these biotic and abiotic factors play an important role in the success growers have with corn production. Integrating all these decisions with each other in a synergistic manner is the cornerstone of a truly integrated pest management program.