Named for their capacity to emit foul-smelling chemicals in the presence of predators or whenever they are crushed, stink bugs are some of the most infamous members of the insect world. While their stench is definitely unpleasant, it isn’t necessarily a problematic attribute. It’s their tendency to feed on plant material, especially throughout the peak growth periods of cash crops, that has earned them their reputation as pests.
In North America, one particular type of stink bug has been identified as a major pest in farms and home gardens. It is commonly referred to as the brown marmorated stink bug (Halyomorpha halys) – BSMB for short. Native to several East Asian countries, this non-native critter can feed on dozens of agriculturally important fruit trees, legumes, and vegetables. Its colonies are able to drain these plants of important fluids, significantly reducing seasonal yield.
Shield-shaped, mottled brown, and just shy of an inch long, stink bugs are able to replenish their numbers year after year. These mobile insects can be extremely challenging to get rid of naturally or by physical means. Few pesticides are specifically manufactured for their control. Attracting the right set of insectivorous predators and growing a few repellent plants may help reduce their spread.
1) Lavender (Lavandula spp.)
Members of the Lavandula genus, known for their alluring scent profiles, are some of the most valuable plants in pest-repellent gardens. English lavender (L. angustifolia), French lavender (L. dentata), and some cultivars of Lavandula x intermedia are in demand for their functional, ornamental, and chemical properties. When these are cultivated in the right locations, they produce a wealth of multi-purpose essential oils.
Lavender oils are rich in phytochemicals like linalool, camphor, and borneol, which have antimicrobial, fungicidal, and pesticidal uses. Collectively, these produce a strong and unmistakable scent – one which induces a state of relaxation in people. In contrast, the identical scent can cause many insects and larger animals to panic and flee.
Stands of lavender or extracts of its essential oil can be your best friend when it comes to protecting your garden. Stink bugs, which use scent to their advantage, are unsurprisingly sensitive to this herb’s heady aroma. Nonetheless, dense stands need to be present to produce an adequately strong repellent scent. Situate them around plots of tender crops to dissuade stink bugs from coming too close.
2) Citronella (Cymbopogon nardus)
Though citronella has minimal value as fodder and as an ornamental plant, it has gained global popularity for the lemon-like scent of its oils. This aggressive member of the Poaceae family forms clumps that measure up to 2.5 meters (8.2 feet) tall. Its lengthy fronds look fairly similar to those of its more popular cousin, lemongrass (C. citratus). Its stems are distinguished from the latter by their broader width and their reddish base.
The essential oil of citronella is now commercially important due to its insect-repellent properties. It contains intensely-scented phytochemicals like citronellal, geraniol, limonene, and citronellol. Other herbs that possess these compounds also tend to bother insects. As these are particularly effective against mosquitoes, they can serve as environmentally-friendly alternatives to chemical repellents.
To repel stink bugs in the garden or around the home, situate pots of citronella grass in key areas (e.g. close to entryways and around vulnerable ornamentals). Avoid growing this species directly in the ground as its rhizomes are likely to compete with the root systems of slow-growing, native plants. You may also make use of homemade sprays containing a few drops of store-bought citronella oil.
3) Peppermint (Mentha x piperita)
This remarkably fragrant herb is undoubtedly one of the easiest to cultivate in moist and sunny parts of the garden. A hybrid between two equally robust species, watermint (M. aquatica) and spearmint (M. spicata), it possesses the best features of its parent plants. Its well-established stands are rarely plagued by grazers and pests in the wild for good reason. The oils in their leaves make them extremely bitter. When exposed and vaporized, the scent masks those of nearby plants.
Recognized as a principal source of phytochemicals like menthol and menthone, peppermint essential oil is commercially important due to its culinary and medicinal uses. It comes as no surprise that it may function as an environmentally-friendly alternative to pesticides.
To discourage stink bugs from laying eggs in and terrorizing your yard, aim to grow a few tufts of peppermint around frequently-damaged ornamentals. Keep in mind that this herb’s roots may aggressively compete with those of neighboring plants. You may consider restricting them to pots or containers.
4) Catnip (Nepeta cataria)
A short-lived herb with a peculiar attractiveness to both domesticated and feral cats, catnip is a wonderful addition to the home garden. This member of the mint family (Lamiaceae) is lovely as an ornamental due to its bright-green, triangular foliage and its fragrant, terminal inflorescences. Visually, it resembles many mint species, with which it also shares some of its major phytochemicals.
Catnip is one of your best options for keeping pests out of your property. It contains an iridoid, called nepetalactone, that can induce unbearable symptoms in many small insects. When insects come into direct contact with substances containing a high concentration of this compound, they can become paralyzed and may never recover. For this reason, nepetalactone-based repellents may be as spatially effective as artificial ones.
To take full advantage of catnip’s bug-repellent properties, make sure its stands are provided with the right growth conditions. Plenty of sunshine and well-draining substrates should enhance the quality of its oils. You may harvest the leaves, cut them up, and spread them around key parts of the home or garden. Store-bought catnip oils can be added to a homemade repellent spray.
5) Garden thyme (Thymus vulgaris)
Another useful member of the mint family, garden thyme can play many roles in an ornamental garden or crop plantation. This evergreen herb has a bushy appearance and a trailing habit, making it ideal as a ground cover plant. Some of its cultivars produce throes of pastel-colored blooms each year. These may be numerous enough to drastically change the appearance of well-established stands. They’ll attract a wealth of pollinators while throwing off unwanted visitors.
Drought-tolerant, garden thyme is often cultivated as a low-maintenance addition to semi-arid or well-draining areas. Its aromatic essential oils are produced in high amounts just before its flowering period. This means that, if you wish for this species to release an adequately strong scent, it would be ideal to harvest some of its shoots before they produce blooms. Depending on the cultivar, this may be in early to late spring.
The biologically active component of thyme essential oil, thymol, repels deer, small grazers, maggots, hornworms, mosquitoes, earworms, stink bugs, and more. Dense stands of garden thyme can also compete with weeds, preventing them from infesting bare and shallow substrates.
6) Zonal geraniums (Pelargonium zonale)
Geraniums are known for their ability to repel many types of scent-sensitive insects, particularly those that have plant-eating life stages. The leaves of zonal varieties are set apart by their scent and their visual features. These are large, crenated, have textural margins, and are usually distinguished by their dark, horseshoe-shaped markings.
The aroma of zonal geranium leaves is given off by a complex essential oil. In the wild, this oil likely functions as a natural deterrent against potential herbivores and pests. Rich in phytochemicals like geraniol, citronellol, and linalool, the oil has anti-bacterial, antioxidant, and anti-cancerous properties as well. Even its secondary compounds, such as pinene, myrcene, and menthone, tend to be unappealing to a wide array of insects and pathogens.
Zonal geraniums can be grown indoors, as formal landscape plants, or as potted ornamentals. Great for flower beds, they can be situated around species that are vulnerable to leaf-eating insects. Do note, however, that they are toxic to pets and may not be the best options for child-friendly gardens.
7) Garlic (Allium sativum)
A staple component of every grocery’s produce section, garlic is now one of the world’s most useful and commercially valuable crops. Of course, it is known best for its distinctly strong flavor – one which can drastically change the taste and scent of even the most commonplace dishes. Its aroma and flavor are generated by its potent mixture of volatile compounds. These are concentrated in its underground bulbs.
Scratching the surface of, or mechanically damaging, garlic cloves triggers a reaction that converts their sulfuric compounds into sharp and hot-tasting chemicals. These include allicin, ajoene, diallyl disulfide, and diallyl trisulfide. Many grazers and plant-eating insects are deterred by these chemicals, which can collectively function as a bio-pesticide.
Simply growing garlic in your garden would not necessarily lead to pest repellency. It would be better to harvest the bulbs, or use store-bought ones, and incorporate their oils into a homemade stink bug spray; thoroughly crush the cloves to release their oils. A garlic-based spray can be directly used on the leaves of many susceptible ornamentals.
8) Radishes (Raphanus raphanistrum subsp. sativus)
Like garlic, the humble radish is able to deter a wealth of pests due to its strongly-scented chemicals. For this reason, it is commonly cultivated as a companion plant for cash crops like broccoli and lettuce. The scent given off by radish bulbs and leaves should help disguise the smell of nearby plants. Moreover, if radish is grown in rows between vulnerable crops, widespread infestations of leaf-eating pests are less likely to occur.
Though radishes are tasty and favorably crunchy to us humans, they are perceived as pungent and unpalatable by many grazers. Extracts of its oil have been shown to be effective as a repellent, with results comparable to that of a commercial insecticide. Rich in phenols, glycosides, and alkaloids, all of its plant parts (including its seeds) can be utilized against stink bugs.
Consider growing this crop as a physical barrier to confuse visiting pests. If you’re able to acquire pure extracts of its oils, you may spray these (in a diluted solution) onto the surfaces of leaves and fruits.
9) French marigolds (Tagetes patula)
The French marigold is unrivaled in its ease of care as a seasonal ornamental. This stunning plant is best known for its vibrant and culturally important blooms. With warm-yellow to reddish-orange hues, these attract beetles and beneficial insects, such as tachinid flies. Though tachinid flies may lay eggs on marigold leaves, they are a welcome sight as they hatch into larvae that may feed on leaf-eating pests.
Apart from attracting stink bug predators, French marigolds tend to be repellent on their own due to the oil glands on their multi-lobed foliage. These emit a pungent odor, one which signals the presence of dangerous phytochemicals to herbivores. Additionally, their roots secrete compounds that protect them from nematodes.
The insecticidal constituents of this species include thiophenes, which are biologically active against a wealth of insects. Due to their volatile nature, they may be difficult to extract and incorporate into an organic pesticide. For this reason, the best way to use marigolds as a stink bug repellent is to cultivate healthy and well-ventilated stands. If this particular species is not available in your area, consider growing its close relatives – Mexican marigold (T. minuta) and African marigold (T. erecta).
10) Purple tansy (Phacelia tanacetifolia)
The purple tansy, also called fiddleneck or lacy phacelia, is commonly found in deserts throughout its native range. It is exceptionally beneficial in the garden and in agricultural setups for a wealth of reasons. First, its blooms attract bees and other pollinators. These can aid in the fruit and seed production of nearby crops. Second, it makes for an eye-catching ornamental due to its lavender inflorescences and its lacy leaves.
Its benefits don’t stop there! Purple tansy can be grown as a natural pest control agent. Its blooms are notorious for attracting insects like hoverflies and parasitic wasps, the larvae of which are able to kill off entire generations of stink bugs and other pests by infiltrating their organs. Any victimized pests have virtually no way of surviving once they are targeted by the predatory larvae.
Though it is winter hardy down to around 18˚F (-7.8˚C), this species is best grown in areas with mild to warm climates and porous substrates. As it is able to self-seed in optimal conditions, it is often used as a cover plant in agricultural landscapes. While it doesn’t repel stink bugs in a direct manner, it does so in a stealthy and ecologically-balanced way – one that highlights the importance of biodiversity!
