Cucumber beetles are insects grouped under the Diabrotica and Acalymma genera. They are often perceived as agricultural pests, especially in areas where gourds of the Cucurbitaceae family are commonly cultivated. Adults are notorious for destroying extensive crop fields as they feed on the young tissues of tender plants. Corn rootworms, which are basically the larval forms of cucumber beetles, can also damage crops by tunneling into the soil and attacking their root systems.
When cucumber beetles and their young move from one plant to another, they may serve as vectors for destructive pathogens. In fact, the losses brought about by their feeding behavior are often minimal compared to that caused by the pathogenic bacteria they carry. Bacterial wilt, signifying the presence of Erwinia tracheiphila, is one such disease. When a plant is infected and has begun to wilt, there is no treatment.
Home gardeners often protect their plants from cucumber beetles and their associated pathogens using mechanical or chemical means. These can end up being costly or harmful to the environment in the long run. Instead, if you are simply growing gourds as a hobby or to meet the needs of your own home, try growing them alongside the right companion plants. Apart from repelling cucumber beetles and their young, these plants should add visual complexity to your garden while increasing its diversity.
1) Nasturtiums (Tropaeolum spp.)
Often cultivated as ornamentals due to their vivid blooms and unique foliage, nasturtiums are some of the most beneficial companion plants in vegetable gardens. These annuals and perennials are set apart by their circular, entire, or multilobed leaves. The most commonly grown type is a hybrid between three hardy Tropaeolum species, namely T. majus, T. minus, and T. peltophorum.
Like many gourds, nasturtiums naturally occur and spread as vining plants. Their trailing stems will eagerly take hold of a trellis and sprawl over those of other crops. While they do attract their own hosts of pests, making them useful as a trap crop, their presence can help prevent cucumber beetle and squash bug infestations. To be effective, however, nasturtium vines should be situated in between those of vining gourds.
The interspersed vines should confuse cucumber beetles and discourage them from making their way up a trellis or feeding on entire beds of young foliage. Of course, this method is not totally reliable, especially if the nasturtiums themselves are under attack from other types of insects. A concerted effort between this vine and other companion plants, in a polyculture or permaculture setup, should work best.
2) Marigold (Tagetes spp.)
Members of the daisy family (Asteraceae), marigolds are lauded as some of the most helpful insect deterrents in ornamental and vegetable gardens. Though their capacity to repel many pests is debated, there’s no doubt that their presence reaps many benefits. It simply can’t hurt to maintain a few stands of these charming flowering plants. Without fail, they’ll attract hordes of pollinators and produce eye-catching blooms.
Hardy to USDA zones 2 – 11, marigolds fare best during warmer months and in frost-free zones. If you’re located in an area that experiences harsh winters, you’ll likely have to grow them as annuals. Some of the best cultivars to use as cucumber beetle repellents include the French marigold (T. patula) and African marigold (T. erecta).
Marigolds can be planted in between rows of cucurbits to evenly spread the reach of their pest-repellent effects. The roots of these plants naturally produce toxins that kill nematodes in the substrate. The scent emitted by their blooms, which may be described as pungent, should deter many adult insects. Moreover, the blooms attract beneficial insects that may feed on or parasitize adult cucumber beetles.
3) Radish (Raphanus sativus)
Who would’ve thought that you could grow one type of vegetable to help protect another from bugs? Often perceived as a salad component and as a forage crop through the cooler months of the year, radish is a surprisingly useful root vegetable. Its flavor and its pungent odor are brought about by a variety of chemical compounds, many of which serve as natural defenses against pests and grazers.
As the radish’s repellent effects extend to cucumber beetles, it makes for a fantastic companion plant next to cucumbers, squash, pumpkins, and melons. Moreover, the presence of radishes is often associated with thriving cucumber plants, leading to a higher overall yield and quality of produce. As radishes also grow quite well next to nasturtiums, these two can be used in concert to repel beetles.
Radishes are root crops, so they are unlikely to make use of the space that cucurbits will require to grow. Both cucumbers and radishes will need to be situated in parts of the garden that receive full sun. The cucumbers should be planted first and provided with support, otherwise they will grow on the radishes. Take note that, as radishes are annuals, they will need to be replanted each year.
4) Common tansy (Tanacetum vulgare)
Commonly known as cow bitter, golden buttons, and common tansy, T. vulgare is a flowering herb with a camphor-like scent. Its aroma is attributed to the presence of toxic compounds in its essential oils. Thujone, one of its phytochemical components, may cause brain damage when it is consumed in large doses. This is why many grazers and leaf-eating insects are wise to avoid its foliage and blooms.
Common tansy can be used as a form of biological pest control alongside many vegetables. It has been proven to reduce the numbers of some types of beetles, particularly the Colorado potato beetle. Its effects should definitely extend to cucumber beetles as well, especially as they rely on the nutrients in plant matter to survive. To an extent, this species can also repel mosquitoes and fleas, making the vegetable garden more welcoming to visitors!
Apart from repelling cucumber beetles and more due to its scent and the presence of toxins in its foliage, tansy can aid in increasing potassium concentrations in the substrate. This should hasten the decomposition rates of waste matter, increasing the number of nutrients that are available to thriving vegetables. Just make sure to handle this plant with caution as contact with its oils can cause an allergic reaction.
5) Broccoli (Brassica oleracea var. italica)
This cool-weather crop is one of the most popularly cultivated cruciferous vegetables because of its favorable nutrient profile and versatility. Interestingly, its bitterness is associated with the presence of glucosinolates. These phytochemicals produce a pungent aroma and have a bitter taste, making them undesirable to some grazers and plant-eating insects. While many cabbage pests are undeterred by these, cucumber beetles may lack tolerance for broccoli’s bitterness.
A study that looked into the effect of intercropping broccoli with cucumbers has shown that this combination of crops can significantly reduce the abundance of striped cucumber beetles (Acalymma vittatum). Control of these beetles invariably led to the reduced occurrence of bacterial wilt disease. These results definitely highlight the potential of broccoli, as well as many other beneficial cucurbit companions, as a natural means of repelling pests in a polyculture setup.
Take note that, to be effective at repelling beetles, your broccoli stands will need to be in good condition. If they are covered in bugs like aphids, cabbage maggots, and loopers, they are more likely to attract pests that will spread to nearby vegetables. Keep in mind that broccoli is a cool weather crop and should ideally be grown when temperatures do not rise to more than 23˚C (73˚F) at most.
6) Catnip (Nepeta cataria)
Though catnip has a knack for bringing out the most euphoric behaviors in cats, it can spell danger to all sorts of insects. A study that looked into the effects of its oils on mosquitoes showed that it can severely harm their nervous system. It’s safe to assume that catnip oil, with nepetalactone as its dominant component, can wreak havoc upon an unsuspecting beetle’s internal organs as well. Moreover, its strong aroma alone should be enough to keep many pests away.
Rows of catnip can be planted in between rows of cucurbits to evenly spread their scent over a given area. Squash bugs and cucumber beetles can be expected to stay clear of catnip shrubs, especially during their bloom period. The lovely inflorescences attract various pollinators and beneficial insects, including those that are likely to parasitize beetles.
Catnips can be grown alongside other flowering herbs with fragrant properties and insect-repellent oils. A combination of compatible herbs can be placed around the periphery of a cucurbit plot or planted directly between rows. If you want to restrict their roots, you may plant them in pots. This way, you can easily move your catnip plants to any area that may require more protection from pests.
7) Onions (Allium cepa)
Onions are another valuable root crop to plant in cucurbit plots. Their presence tends to keep a variety of scent-sensitive, leaf-eating insects away from the vegetable garden. When strategically situated in small cucumber patches, the scent and taste of onion leaves should help reduce the chances of cucumber beetle infestations. This crop can also be planted in a circular formation around patches of tomatoes and carrots to keep aphids and maggot flies away.
Now cultivated all across the globe due to their culinary importance, onions naturally produce an essential oil with pesticidal properties. The oil’s phytochemicals are responsible for providing the bulb with its strong smell and taste. Though these are safe for humans to consume in conservative amounts, they are toxic to smaller mammals like dogs, cats, and rodents.
In some parts of Europe, onion oil is now used as a natural repellent in organic vegetable farms specializing in umbellifers (carrots, fennel, celery, etc.). Interestingly, instead of spraying the oil onto the foliar surface of these crops, it is placed in containers around patches that require more protection from pests. The strong scent of the oil masks the presence of susceptible vegetables.
8) Common sage (Salvia officinalis)
A fragrant herb with a rich history, sage is believed to be instrumental in cleansing the energy of a space and in keeping evil forces away. Though the use of sage for these purposes is wholly anecdotal, there may be some truth to it in a more literal sense. S. officinalis leaves, cuttings, and its pure oil extracts have the potential to repel troublesome pests and grazers.
Heavily cultivated for its essential oils and for culinary purposes, sage has a bitter flavor and a musky or earthy scent. The type of cultivar grown, as well as the nutrient concentrations and mineral profile of the substrate, can influence the strength of this herb’s aroma and taste. Rubbing the leaves or cutting the shoots to expose their oils allows for a stronger scent to waft through the herb garden.
Maintaining healthy stands of sage in between or around patches of cucurbits should help mask their scent and repel cucumber beetles. The presence of bitter foliage should also discourage them from infesting the vegetable garden and spreading their associated pathogens.
9) Calendula (Calendula officinalis)
Also known as pot marigold, calendula is a fantastic aromatic herb for both ornamental and culinary use. It is regarded as one of the most straightforward flowering plants to grow by many novice and experienced gardeners. If you’re just starting to develop your skills and knowledge as an organic vegetable grower, this is definitely a great companion plant with which to experiment and have fun!
When planted around a vegetable patch, calendula should aid in repelling various pests, including cucumber beetles, asparagus beetles, tomato hornworms, and nematodes. As it is hardy to zones 9 – 11, it is generally cultivated as an annual plant in temperate zones. It thrives best in parts of the vegetable patch that are fully exposed to sunlight. Partial shade is also tolerated if the roots are planted in well-draining substrates.
Calendula extracts from stems and edible blooms contain various phytochemicals with antibacterial and antifungal properties. Even its dried pollen and flowers continue to possess pesticidal properties. You can thus sprinkle these around key parts of cucurbit patches.
10) Rue (Ruta graveolens)
Named for its bitter leaves, which have led many of its consumers to regret partaking in them, rue is unsurprisingly packed with insecticidal phytochemicals. The bluish-green leaves, which are distinctly multi-lobed, release a heavy and fragrant aroma upon being brushed or damaged. The scent should help mask vulnerable and appetizing vegetables, like cucumbers, tomatoes, and the like.
To incorporate rue as a companion plant in your cucumber or squash patch, make sure to situate its stands close to the vegetables you wish to protect. You may either plant it in rows in between trellises of cucumbers or you may opt to plant it evenly around a cucurbit patch. Whichever arrangement you choose should help minimize the spread of cucumber beetles.
Keep in mind that a polyculture setup involving other repellent plants and trap crops should work best. If you’re interested in using rue as a pest barrier, plant it alongside nasturtiums, marigolds, or other fragrant herbs that are unlikely to compromise the growth of your cash crops. If you wish for rue and its companions to attract beetle predators, allow its shoots to bloom.
