The brown marmorated stink bug (Halyomorpha halys), an invasive species introduced from Asia, has become a widespread and frustrating garden pest. This insect feeds on a wide range of fruit, vegetable, and ornamental plants, making its management a necessity for gardeners. Dealing with these shield-shaped invaders requires a layered strategy that prioritizes non-chemical methods before escalating to targeted interventions. This approach ensures the protection of your harvest, beneficial insects, and the overall garden ecosystem.
Recognizing the Threat and Damage
The adult brown marmorated stink bug is easily recognizable by its distinct shield shape, mottled brown coloration, and a size similar to a US dime. They also feature alternating light and dark bands on the last two antennal segments, which helps distinguish them from native stink bug species. The nymphs, or immature stages, are rounder and vary in color, often showing yellow, red, and black markings as they develop.
The damage caused by these pests results from their piercing-sucking mouthparts, which they use to extract plant fluids from leaves, buds, and developing fruit. On fruits like tomatoes, peppers, and apples, this feeding causes pitting and scarring on the surface, often leading to a corky or mealy texture underneath. Leaf damage typically appears as small, light-colored stippled spots, and severe infestations can lead to significant crop loss and fruit deformation.
Exclusion and Manual Removal Strategies
The most immediate and non-toxic method for managing stink bugs is through physical exclusion and active manual removal. Installing fine mesh row covers over susceptible plants prevents the adult insects from landing, feeding, and laying their characteristic barrel-shaped egg clusters. For this method to be effective, the covers must be secured tightly around the perimeter to prevent the bugs from crawling underneath.
Active removal, particularly handpicking, is highly effective for smaller infestations and requires a simple bucket of soapy water for disposal. When disturbed, stink bugs will often drop to the ground rather than flying away, making it easier to capture them by holding the bucket directly beneath the insect before nudging it. The soap breaks the surface tension of the water, causing the bugs to quickly drown and preventing them from releasing their defensive odor.
Manual removal is most successful in the cooler hours of the day, such as early morning or late evening, when the bugs are less active. Specialized handheld vacuums can also be used to quickly collect large numbers of insects without crushing them, which helps to contain the foul odor. Regularly inspecting plants, especially the undersides of leaves where eggs are laid, allows for the early removal of clusters before they hatch into damaging nymphs.
Utilizing Natural and Biological Controls
For gardeners seeking moderate-impact solutions, a range of natural and biological controls can suppress stink bug populations.
Insecticidal Soaps and Diatomaceous Earth
Insecticidal soap sprays work by dissolving the insect’s protective outer layer, leading to dehydration and death upon contact. Commercial insecticidal soap products, which contain potassium salts of fatty acids, are specifically formulated to be less harmful to plants. These contact sprays must be applied directly to the insects, covering both adults and nymphs, and are most effective when applied during the cooler times of day to prevent leaf burn.
Another physical control involves food-grade diatomaceous earth (DE), a fine powder made from fossilized aquatic organisms. The abrasive silica particles damage the stink bug’s exoskeleton as they crawl over it. DE must remain completely dry to be effective and should be reapplied after rain or heavy watering.
Natural Enemies
The presence of natural enemies offers a long-term, sustainable control measure for the garden ecosystem. Generalist predators like praying mantises, spiders, and certain predatory stink bugs will consume eggs and nymphs, helping to reduce the overall population pressure. More specific biological control is offered by parasitic wasps, particularly the tiny, non-stinging Trissolcus japonicus, also known as the Samurai wasp, which lays its eggs inside the stink bug’s eggs, preventing them from hatching.
Targeted Chemical Intervention
Chemical treatments should be reserved as a final option for severe infestations that threaten a significant portion of the harvest. Organic-approved insecticides often contain pyrethrins, which are botanical extracts derived from chrysanthemum flowers that provide fast knockdown by disrupting the insect’s nervous system. These contact-based sprays are biodegradable and break down quickly in sunlight, making them a preferred choice in a food garden environment.
When using any insecticide, it is crucial to follow the label instructions precisely, especially regarding the pre-harvest interval (PHI), which is the minimum time allowed between application and harvesting the crop. Application should be highly targeted, focusing only on infested areas and avoiding broadcast spraying to minimize harm to beneficial insects and pollinators. Applying these products in the late evening, after pollinators have returned to their nests, helps to reduce the risk of non-target harm.