This project will address the emerging concern of farmers on the Eastern Shore of Maryland that stink bug species use cover crops as overwintering habitats. Fall-planted cover crops have many benefits to soil health and the environment, and their use in Maryland is likely to increase in the future. However, we hypothesize that specific cover crop mixes, timing of cover crop termination relative to soybean planting, and the relative composition of soybean fields and woodlots in the farming landscape will affect stink bug populations and their potential risk to soybean production. To optimally implement a practical best management approach to this stink bug problem, we first need to address how these cultural practices and landscape factors affect stink bug populations and their movement from cover crops to soybean fields.

Several native species of phytophagous stink bugs, including the green stink bug, Acrosternum hilare (Say), brown stink bug, Euschistus servus (Say), and southern green stink bug, Nezara viridula (Linnaeus), are known economic pests of soybean. Although the brown and green stink bugs have been reported as far north as Quebec, they are more often injurious in the southern states. However, climate change resulting in warmer winters has allowed these stink bugs to overwinter successfully in more northern locations in the US. Brown and green stink bugs are commonly found in most Maryland soybean fields in late August through to harvest. Furthermore, the brown marmorated stink bug (Halyomorpha halys) is an invasive species from China that is now present in soybeans throughout Maryland, causing delayed growth at the field edges, especially next to woodlots. The economic impact of this species has been generally higher in western and central Maryland, where there are more woodlots around fields to serve as the preferred overwintering habitat and early-season food source for the 1st generation.

Stink bugs use their piercing, sucking mouthparts to feed on plant juices from the foliage and pods. Their feeding injury on soybean pods causes discolored, shriveled beans and reduces the yield and quality of the beans. In addition to the mechanical injury to the seed, they can transmit disease organisms. Feeding on younger seed pods results in a significant yield reduction. The degree of damage depends to some extent on the developmental stage of the seed when fed on by the stink bug. However, little is known about stink bug feeding injury during the early soybean vegetative stages. For instance, stink bugs infesting seedling corn can cause stunting, deformed tillers, and often plant death.

Stink bugs overwinter as adults in protected areas such as fence rows, grassy field borders, under stones, or tree bark. They become active during the first warm spring days, typically in April. They will mate, and females usually start depositing eggs in June. These eggs are laid in clusters of 20-30, primarily on leaves and stems but also on pods. Nymphs hatch from these eggs and pass through five instars before becoming adults. Approximately 5 weeks elapse between hatching and adult emergence. Adults live a long time, with most species having one generation per year in Maryland. Adult stink bugs generally reach their highest population levels in September, when they can become an economic problem for soybeans. We believe that cover crops may provide a suitable overwintering habitat for stink bugs, which then move into soybean fields after cover crop termination and thus can potentially cause similar injury to seedling soybeans.

This project addresses the emerging concern that phytophagous stink bug populations are increasing due to higher overwinter survival and are utilizing cover crops for shelter and food. We will determine the species and population densities of stink bugs that overwinter in cover crops and whether they favor certain mixtures of cover crops.

With the help of extension educators and crop advisors and in cooperation with growers, we will select at least 25 fields planted in different types of cover crops. Each field will be planted with soybeans. Fields will be equally located in the lower and upper regions of the Eastern Shore, where there have been more reports of stink bug problems. The type of cover crops and the anticipated termination timing relative to soybean planting will vary among fields and the surrounding landscape area relevant to the proportion of woodlot area.

Starting in early spring, each field will be geo-referenced using Google Maps to identify the density of woodlots and their distances to each field. Sampling of each field will begin around 45-30 days before the expected termination time of the cover crop. We anticipate that stinkbugs will have terminated their overwintering diapause behavior and are actively feeding and reproducing in the cover crop. Two biweekly visits will be made to each cover crop to assess the stink bug species present, their population densities, and whether they are actively reproducing, as evidenced by the presence of nymphs. Densities of adults and nymphs (small, medium, large) will be determined by taking 10 sweeps with a standard sweep net at five areas across each field. As an alternative sampling method, beat sampling to dislodge stink bugs from a unit area of the vegetation may be needed to estimate density, depending on the height and vegetative structure of the cover crop. Once the cover crop is terminated and the established soybean crop has reached the seedling stage, further sampling of each field by direct visual counts will be conducted at least twice to assess the presence and density of stink bugs during the early vegetative stages of soybean growth. In addition, visual observations will determine if soybean seedlings have any growth disorders attributed to stink bug feeding.

Data on stink bug density recorded in the cover crop and then later in the soybean crop in each field will be analyzed using correlation analysis to determine if stink bug populations in the soybean fields are related to densities in the cover crop. We will also use multivariate analysis to identify the influence of the cover crop mix and distance to woodlots on observed patterns in stink bug populations.

Updated August 1, 2025:
Between mid-April and mid-May, 26 cover crop fields were sampled on the Eastern Shore of Maryland. The fields sampled included 75% planted with winter wheat and 25% with a mixture of cover crops, including rapeseed, rye radish mixture, rye winter pea mixture, and a winter wheat clover mixture. Due to the low number of sampled fields planted with a mix of cover crops, no conclusions about stink bugs’ preference for overwintering cover crops can be drawn at this time. Therefore, only wheat cover crops will be evaluated. Densities of adults and nymphs were determined by taking ten sweeps with a standard sweep net at five to ten areas across each field. Fourteen fields were sampled twice during the cover crop stage. The other fields were sampled once due to weather constraints before terminating the cover crop. Six fields were sampled again in June when soybean plants were 6-8 inches high. Sampling of stink bugs in soybeans is ongoing.

91 adult stinkbugs were found while sampling cover crops. The brown stink bug, Euschistus servus (Say), and the brown marmorated stink bug, Halyomorpha halys, made up 98% of the species found. The green stink bug, Acrosternum hilare (Say), and the red-shouldered stink bug, Thyanta curator, made up the other 2%. On average, fewer than two stink bugs were found per field. Most of the stinkbugs were found after May 1. During sweeps, over 200 ladybird beetles (adults and larvae) were counted. Tarnished plant bugs (Lygus lineolaris) and aphids are other pests found on cover crops.

Early data on this project was shared with growers at the 2024 Maryland Community Classic.

Updated August 1, 2025:
Between April 20 and May 8, 2025, 13 cover crop fields were sampled across the Mid-Shore counties. Densities of adults and nymphs were determined by taking twenty sweeps with a standard sweep net at ten to twenty locations across each field. Seven fields were sampled twice for a total of 20 scouting events. The fields sampled included ten that were planted with winter wheat and three planted in a mixture of cover crops, including rapeseed, wheat pea mixture, and rye radish mixture. Five fallow fields were also scouted, but no stink bugs were found in them. Cover crop fields were visually shorter and thinner in 2025 compared to 2024.

Eight adult stinkbugs were found while sampling cover crops. All were found in winter wheat fields. Six were found near the edge of the field next to a road.
Seven were brown stink bugs, Euschistus servus (Say), and one was a brown marmorated stink bug, Halyomorpha halys. No stink bug nymphs were found. On average, fewer than one stink bugs were found per field. During sweeps, 17 spiders were counted, and 46 ladybird beetles (adults and larvae) were counted. A few different caterpillar species were also found, including two armyworms in wheat fields. No soybean fields were scouted in 2025.

Results from the 2024 study were shared with local growers via the UME agronomy newsletter and winter production meeting. A poster was presented on this research at the 2025 NACAA meeting.

The PIs are highly grateful to the support of the farmers who allowed us access to their fields and the Maryland Soybean Board for funding this research. Please contact Emily Zobel ( ezobel@umd.edu with any additional questions.

Updated February 3, 2025:
See attached PDF.

During the 2024 growing season, we scouted 37 cover crop fields along the Eastern Shore of Maryland for stink bug populations. Fifty-one sampling events took place in cover crops between mid-April and mid-May. Of the sampled fields, 30 were planted with winter wheat, and seven were a mixture of cover crops, including rapeseed, rye radish mixture, rye winter pea mixture, and a winter wheat clover mixture. Due to the low number of sampled fields planted with a mix of cover crops, no conclusions about stink bugs’ preference for overwintering cover crops can be drawn based on this field survey. Only wheat cover crops will be evaluated in the results for year one.

During the 2025 growing season, 13 cover crop fields were sampled across the Mid-Shore counties. Densities of adults and nymphs were determined by taking twenty sweeps with a standard sweep net at ten to twenty locations across each field. Seven fields were sampled twice for a total of 20 scouting events. The fields sampled included ten that were planted with winter wheat and three planted in a mixture of cover crops, including rapeseed, wheat pea mixture, and rye radish mixture. Five fallow fields were also scouted, but no stink bugs were found in them. Cover crop fields were visually shorter and thinner in 2025 compared to 2024.

Only adult stink bugs were found in cover crops, suggesting no reproduction occurs in spring cover crops. In 2024, a total of 101 stink bugs were counted across the 51 scouting times, averaging 1.98 stink bugs per field per scouting date. The majority of stink bugs counted were brown stink bugs (85%), followed by brown marmorated stink bug (13%) and red-shouldered stink bugs (Thyanta pallidovirens) (2%). Most stink bugs were counted during the last week of April (23%) and the first week of May (59%). Along with stink bugs, ~225 ladybird beetles (Coccinellidae), adults, and larvae were counted. Approximately 75 tarnished plant bugs (Lygus lineolaris) were counted. Following cover crop termination, eight fields were selected and sampled again in June and July. Eleven brown stink bugs total were found during the scouting of soybean seedlings. Of these eleven, six were found in the same field on the same date, which is below the treatment threshold of 8 stink bugs per 20 sweeps for the production of soybeans. No soybean seedling disorders attributed to stink bug feeding were seen.

In 2025, eight adult stinkbugs were found while sampling cover crops. All were found in winter wheat fields. Six were found near the edge of the field next to a road. Seven were brown stink bugs, and one was a brown marmorated stink bug. No stink bug nymphs were found. On average, fewer than one stink bugs were found per field. During sweeps, 17 spiders were counted, and 46 ladybird beetles (adults and larvae) were counted. A few different caterpillar species were also found, including two armyworms in wheat fields. No soybean fields were scouted in 2025.

The low number of stink bugs found in spring cover crops suggests that stink bugs do not overwinter or move into late-season cover crops. Given the increased cost of pesticides and the issue of pesticide resistance, adding an insecticide to cover crop burndown spray or early weed control is not necessary for controlling stink bugs unless field scouting indicates otherwise.

The PIs were extremely grateful for the support of the farmers who allowed us access to their fields and the Maryland Soybean Board for funding this research.
Please contact Emily Zobel (410-228-8800, ezobel@umd.edu) with any additional questions.

This project will address the emerging concern of farmers on the Eastern Shore of Maryland that stink bug species use cover crops as overwintering habitats. Fall-planted cover crops have many benefits to soil health and the environment. Late-season burndown of these cover crops has been shown to increase these benefits by allowing cover crops more time to grow, leading to more biomass, better weed control, more soil carbon, and better soil structure.

If cover crops are affecting local stink bug populations by providing habitat, as seen with the slug population, then there is a potential risk to soybean production that requires farmers to use the best management approach to reduce the stink bug population and future yield damage. However, if cover crops are not affecting local stink bug populations, then farmers may be wasting funds on unneeded pesticide inputs.

This project investigated the species and population densities of stink bugs in late-season cover crops, whether they favor certain mixtures of cover crops and their potential movement from cover crops to soybean fields.