The infamous squash bug, scientifically known as Anasa tristis, is one of the most common and problematic pests in vegetable gardens. Adult squash bugs are winged and have a single pair of antennae. They may appear greyish-brown or flattened when viewed from the top. Their abdomen, in contrast, is quite colorful as it has bright brown and orange stripes. Measuring less than an inch long, they may be difficult for the untrained eye to spot.
Named for their tendency to attack members of the cucurbit family (i.e. melons, pumpkins, squash, cucumbers, etc.), these bugs target nutrient-rich leaves. Equipped with toxic saliva and with mouthparts for sucking sap and piercing leaf tissues, their feeding habits can cause plants to turn brown and eventually wilt. During the peak of their growth period, their life stages may overlap. Both the eggs and nymphs are usually found on the undersides of leaves.
Though physical measures of squash bug control may help minimize the spread of small populations, these are usually time-consuming and unreliable. Chemical pesticides are often used for large-scale farms, but these tend to have environmental consequences. If you intend to cultivate a small cucurbit garden, it would be best to impose biological control on squash bugs with the help of a few well-selected plants.
1) Radish (Raphanus raphanistrum subsp. sativus)
Radishes are widely cultivated for their edible root crops. Crunchy, strongly scented, and slightly spicy, these are rich in complex phytochemicals, many of which aid in protecting the plant from pests and diseases. This forage crop is often used as a companion plant by novice and experienced gardeners. Its rapid growth rate and low-maintenance requirements make it a wonderful and stress-free addition to vegetable gardens in the backyard.
Growing radishes next to susceptible members of the cucurbit family, such as zucchini, has been shown to be a promising method of squash bug control. The pungent compounds of radishes include myrosinase, glucosinolate, and isothiocyanate. When grown extensively around and in between rows of squash, radishes may be as effective at repelling squash bugs as some chemical pesticides, such as Sevin.
Other vegetables and herbs that grow quite well when planted next to radishes include lettuce, peas, cucumbers, nasturtiums, and chervil. Note that merely increasing the biodiversity of a vegetable garden is already remarkably effective when it comes to pest control. However, even radishes can attract a unique set of pests, especially in suboptimal growth conditions.
2) Catnip (Nepeta cataria)
A fantastic perennial herb for home gardens, catnip is an attractive and ecologically beneficial plant. Its dense stands attract butterflies and predatory insects, such as lacewings. Once widely cultivated for its herbal uses, its modern-day popularity is largely due to its appeal to cats. However, while the leaves can induce a sense of euphoria in both domestic and wild types of cats, they are notorious for repelling all sorts of pestilent insects.
Nepetalactone, the active ingredient in catnip oil, naturally functions as an insect repellent. This aromatic monoterpene is capable of triggering painful sensations as it targets chemical receptors in the nervous system of scent-sensitive pests. When pests like squash bugs, mosquitoes, flies, and cockroaches catch a whiff of its scent, they are likely to back away.
Intact catnip leaves give off a faint scent, but mechanically damaging them should release a stronger and more expansive scent coverage. This is why extracts of catnip essential oil tend to be more potent and effective. Catnip is great as a companion plant for some susceptible crops, but keep in mind that it would need to be present in dense stands to reliably keep squash bugs away.
3) Marigold (Tagetes spp.)
Marigolds are grown all over the world for their aromatic foliage, vibrant blooms, and ease of care. These members of the Asteraceae family also have a reputation for being some of the best companion plants around plots of vegetables. They attract a wealth of beneficial insects, some of which are likely to feed on various life stages of common pests.
Marigolds won’t kill existing squash bugs, but they can help prevent them from reproducing like wildfire around a squash or cucumber patch. The scent given off by a high density of marigold leaves should repel reproducing adults and force them to search for less hostile conditions elsewhere. These herbs can be grown as a hedge or border to serve as a natural perimeter for warding off grazers.
The most popularly cultivated marigolds, which include the French marigold (T. patula), Mexican marigold (T. erecta), and signet marigold (T. tenuifolia) contain phytochemicals with insecticidal and nematicidal activity. Extracts of the sap from the leaves and blooms contain volatile flavonoids, monoterpenoids, and thiophenes, some of which are toxic to insects.
4) Nasturtium (Tropaeolum spp.)
Nasturtiums are a versatile group of flowering annuals and perennials. These plants are known for having fleshy stems and flexible leaf stalks, which can twine around supporting structures much like the tendrils of vines. The most popular types, hybrids between three parent Tropaeolum species (T. majus, T. peltophorum, and T. minus), have stems that readily scramble over other plants, trellises, and fences.
Though squash bugs are able to thrive on the leaves of many vining cucurbits, they can be counted on to keep away from the vining stems of nasturtium. The latter thus makes for a fantastic companion plant. As a bonus, instead of just growing it around or in between susceptible crops, its stems can be trained to trail through clumps of squash and melon. Their leaves are likely to mask the scent of the surrounding foliage.
For nasturtiums to be effective as companion plants in a vegetable garden, they would need to be adequately abundant. A single healthy nasturtium won’t do the trick. Intercropped rows of this plant, alongside other squash bug-repellent herbs, are recommended. Do note that it may attract its own pests as it also functions as a trap crop for aphids and flea beetles.
5) Peppermint (Mentha x piperita)
Given its remarkably strong fragrance and flavor, it comes as no surprise that peppermint is one of the most useful natural pesticides in a horticulturist’s arsenal. This mint hybrid is packed with an essential oil that readily leaks out of damaged stems and leaves. Simply rubbing the surface of a peppermint leaf should release its distinct scent, which can signal the presence of toxins to many leaf-eating pests.
Peppermint essential oil contains volatile phytochemicals like menthol, neomenthol, menthone, and caryophyllene. In conservative doses, these compounds can impart many pharmaceutical uses for a wide range of human ailments. In contrast, they spell hostility to a diversity of unwanted insects in the home garden; direct contact with the oils can damage their nervous systems and prevent them from sniffing out their target plants.
To repel squash bugs with peppermint, you may either grow this hybrid in rows around susceptible vegetables or use its leaves and oils in a more direct manner. Peppermint leaves can be harvested, cut up, and sprinkled around plots of cucurbits. You may also incorporate the oils into a water-based spray and target leaves with suspected infestations.
6) Common tansy (Tanacetum vulgare)
Known best for its clusters of button-like, yellow blooms, the common tansy has long been used to treat a range of commonplace ailments. Once believed to be a natural treatment for skin purification, joint pain, and all sorts of reproductive ailments, its rich history is a testament to the volatility of its essential oil. Tansy is rich in phytochemicals like thujone, camphor, myrtenol, and 1,8-cineole.
Sixty to seventy years ago, tansy was already used alongside pennyroyal and fleabane as a source of insect-repellent oils. It was also placed on windowsills and above linens to repel flies, ticks, and ants. When grown alongside members of the Cucurbitaceae family, it can help mask the scent of their nutritious leaves and deter pests like Colorado potato beetles, squash bugs, cucumber beetles, and even mice!
Growing rows of tansy in between susceptible crops should draw beneficial insects and prevent squash bug infestations. Both intact and dried tansy flowers can be crushed and distributed around key parts of a vegetable plot. Make sure to use gloves when handling this staunch plant as its oils may cause contact dermatitis.
7) Garlic (Allium sativum)
The humble garlic bulb has been in cultivation for hundreds of years. Set apart by its odorous cloves and its leafy, flowering stem, it is one of the most important components in dishes throughout its native range. Sheathed by specialized leaves, its bulbs can be grown in containers and in well-drained soils of tilled, sun-exposed plots. Though its summer flower heads may have some ornamental value, it is seldom the reason for which this herb is dedicatedly grown.
The value of garlic is largely concentrated below ground. Though its bulbs may attract some pests in intensive, monoculture farms, they tend to be more repellent in diverse vegetable gardens. When the cloves are damaged, they release a potent, sharp, and unmistakable odor. This is facilitated by enzymes that trigger the breakdown and release of sulfuric compounds like allicin and ajoene.
Unfortunately, wholly intact garlic bulbs are rarely effective at repelling aerial pests. As their spicy scent and potent oils are released upon mechanical damage, you’ll need to harvest and crush the bulbs to create a squash bug repellent. Mix crushed garlic into a water-based solution and target the leaves and stems of cucurbits.
8) Oregano (Origanum vulgare)
A member of the mint family (Lamiaceae), oregano is often grown in ornamental herb gardens. Its olive-green, leathery leaves arise in opposite pairs along the length of upright stems. In summer, it produces erect spikes of pink to purple blooms. These attract bumblebees, butterflies, and many beneficial insects. Several cultivars have gained the RHS Award of Garden Merit for their eye-catching foliage, medicinal uses, and ease of care.
Oregano leaves are slightly bitter and earthy due to the presence of a phytochemical-rich essential oil. Though the oils impart a unique flavor to many culinary dishes, it is detested by a wide range of herbivores and leaf-eating insects. Rich in compounds like carvacrol, thymol, and p-cymene, it has a knack for keeping pests away from patches of herbs and flowering perennials.
To take advantage of oregano’s pest-repellent properties, grow it in dense rows or hedges around and in between rows of squash, cucumber, and melon. Occasionally trim the shoots to release a stronger scent. Don’t toss away the cuttings as these can be crushed up and scattered around other plots of plants. Their strong scent should force squash bugs to think twice before calling your garden home.
