A spring or summer’s frolic would be incomplete without at least one friendly beetle encounter. Grassy fields or wildflower gardens, full of food and sites for shelter, are favored by these little critters. June bugs are especially common during warm months when their adult forms emerge from the soil and begin feeding on vegetation. These scarab beetles (subfamily Melolonthinae) come in hundreds of widely distributed species.
In relatively developed areas, you’re most likely to encounter six types of June bugs. These include the common June beetle (Phyllophaga spp.), green June bug (Cotinis nitida), green fruit beetle (Cotinis mutabilis), Japanese beetle (Popillia japonica), ten-lined June beetle (Polyphylla decemlineata), and European chafer (Rhizotrogus majalis).
Found all throughout North America, these warm-weather beetles are relatively harmless to humans. They can, however, damage your garden by feeding on foliage and young roots. Even their long-lived larvae can ruin crops. These flying bugs don’t act as pollinators, though they do move from one plant to another. To prevent them from causing extensive damage, consider growing pest-repellent plants.
1) Rosemary (Salvia rosmarinus)
This modest herb, which can develop into an increasingly woody shrub, is one of the most useful perennials. Apart from having ornamental value, its leafy shoots contain potent phytochemicals with repellent properties. Mechanically damaging the leaves releases chemicals in the form of a pungent and bitter-tasting oil. Though humans can appreciate the oil’s aromatic properties, most grazers and insects find it unbearable.
June bugs are highly unlikely to feed on the leathery foliage of rosemary shrubs. They prefer delicate, neutral-tasting, and soft foliage, such as those produced by strawberry plants, corn, and field grasses. Stands of rosemary should be left largely untouched by pests and larger grazers, so they can be used to shield or block the scent of more palatable ornamentals. Intercropping rosemary with susceptible crops may lead to desirable results.
Note that cultivating a few rows of rosemary may not be effective against existing infestations of June bugs. Though these beetles will avoid fragrant herbs, their scent cannot solely be relied upon to prevent their spread, especially when their juvenile life stages continue to develop in the substrate.
2) Lavender (Lavandula spp.)
Though we find the scent of lavender oils relaxing and pleasant, hardly any grazers or insects are able to tolerate it. In fact, bees are some of the only animals that will intentionally approach dense stands of lavender during its bloom period. Leaf-eating insects, such as June bugs, find the phytochemical-rich leaves unpalatable.
Lavender oils include varying concentrations of linalool, camphor, cineole, limonene, and caryophyllene. A fair share of their components likely evolved as a means of self-defense, preventing their wild stands from being attacked and consumed by pests. Their presence, especially in ornamental gardens, can help discourage June bugs from feeding on tender plants and laying their eggs.
Cuttings of lavender plants can be distributed around plots of sensitive species. You may also use pure extracts of their oils to create a topical repellent or antifeedant for frequently-damaged crops. Add the oils to a homemade, water-based spray and target parts of the garden where you’ve previously spotted these beetles.
3) Peppermint (Mentha x piperita)
Members of the Mentha genus are known for being some of the most effective natural repellents in herb gardens. Peppermint, a wild hybrid between water mint (M. aquatica) and spearmint (M. spicata) produces a remarkably potent and fragrant oil. When this oil’s aroma is released by mechanical damage or by rubbing the leaves, it can signal the presence of poison and danger to nearby insects and grazers.
Pesky June bugs tend to avoid coming too close to densely planted peppermint stands. You can thus use this hybrid to create a natural barrier around vulnerable crops and ornamentals. Grow its rows around flower beds to deter both the larvae and adult beetles from snacking on young foliage. You can also collect cuttings and peppermint leaves, chop them up, and sprinkle them around the vegetable garden.
For a more surefire way of driving out beetles, try making use of peppermint extract. Rich in menthone, limonene, pulegone, and pinene, the oil has been proven to be effective against insects and rodents. June bugs can be expected to stay away too! Essential oil droplets can even be placed in substrates where beetle larvae are occasionally sighted. Their repellent effects should help protect the roots of plants from subterranean pests.
4) Catnip (Nepeta cataria)
Popularized by and named for its unusual effect on cats, catnip closely resembles other members of the mint family (Lamiaceae). This fascinating species grows to about 40 inches (1 meter) tall, producing shoots with oppositely arranged pairs of fragrant leaves. It typically grows in moist and disturbed areas. Well-established specimens tend to spread on their own via the horizontal growth of short rhizomes.
All life stages of June beetles can be expected to avoid catnip colonies. Their pungent stands mask the scent of more palatable plants while attracting many beneficial insects and potential predators. Catnip blooms attract parasitoid wasps, which can serve as an ecologically friendly biocontrol tool for pest infestations. These wasps produce eggs and larvae that can feed on beetles (or their eggs and larvae) from within.
Catnip extract has yet to be proven effective against June beetles, though it is likely to be avoided due to its phytochemical ingredients. Nepetalactone, a dominant active compound in catnip oil, can adversely affect the nervous system of insects. By intercropping this species with leafy greens, its oil-rich leaves should dissuade herbivorous beetles from infesting cash crops.
5) Tomato (Solanum lycopersicum)
Though tomato is an unlikely addition to lists of pest-repellent plants, it is a promising deterrent toward June beetles. It’s definitely not the tomato fruit that the beetles will stay away from, however. The mechanism with which tomatoes can help control infestations lies in their leaves. Their extracts have shown potential as a source of pesticidal phytochemicals. These can prevent troublesome insects, such as fruit flies, from laying their eggs on vulnerable crops.
The oils of tomato leaves contain a combination of flavonoids and phenolic compounds. While these phytochemicals principally function as antioxidants in plant cells, they may also be toxic to some types of insects. Of course, their presence in intact leaves may do little to keep the hungriest animals away. To keep beetles at bay, the oils may need to be collected and applied directly onto the outer surfaces of delicate leaves.
The next time you spot June bugs in your vegetable garden, try harvesting some tomato leaves. Finely chop about two cups of leaves and soak them in an equal amount of water for a few hours. Remove any leaf particles from the solution using a strainer or porous cloth and transfer the liquid into a spray bottle. Target zones of the garden that are frequented by beetles and other pests.
6) Citronella (Cymbopogon nardus)
In terms of scent and appearance, citronella closely resembles its more popular cousin, lemongrass (C. citratus). When it comes to repelling insects, however, the former serves as a source of one of the most effective repellent oils in nature. Rivaling the effects of DEET, an industrial-strength insecticide, citronella essential oil works by masking other scents. Its overpowering aroma makes it difficult for bugs to locate their intended targets.
Extensively studied against flies, mosquitoes, and ticks, citronella contains phytochemicals like citronellal and geraniol. Other herbs that contain these compounds also tend to be somewhat effective as natural pest repellents. In high doses, citronella foliage is toxic and can lead to unpleasant gastrointestinal symptoms. This is why its dense, potentially invasive, stands can lay waste to pasturelands.
If you intend to cultivate citronella grass for its repellent properties, consider restricting its roots to pots, containers, or dedicated plots. Potted specimens can be placed in rows around susceptible ornamentals and leafy crops.
Controlling June Bugs in the Soil
The larval form of June bugs can last for up to 3 years! This means that, for most of these insects’ lives, they persist as protein-rich “white grubs” in the soil. They do little other than feed on roots, fallen leaves, and decaying plant parts during this stage of growth. When present in large populations, June bug larvae can quickly decimate entire plots of ornamentals and crops. The initial phases of damage may be unnoticeable, though they severely affect how efficiently plants can take up necessary nutrients.
For these reasons, June bug control may involve targeting the substrate instead of just the aerial parts of sensitive plants. Applying diatomaceous earth to the soil surface is one chemical-free means of reducing the chances of infestations. Made of fossilized diatoms (a type of algae), it can cause insects to dry out. Moreover, when it is spread over the soil’s surface as a powder, its particles are sharp enough to pierce the outer tissues of surfacing larvae and small beetles.
It’s best to apply diatomaceous earth towards the end of spring or at the beginning of summer, which is when adult June bugs emerge. Make sure to target patches of plants or turf where they are most likely to congregate.
Attracting Natural Predators to Control June Bug Populations
Attracting natural predators is another great way to complement the repellent effects of plants on June bugs. Birds, spiders, snakes, rodents, bats, flies, and parasitic wasps will eagerly target and feed on these protein-rich beetles. In the wild, these animals are partly responsible for maintaining healthy populations of insects, preventing them from causing extensive damage to the environment.
To attract these predators, aim to maintain a biodiverse garden. Birds can be drawn to your garden by growing the right set of berry-producing shrubs and herbs. Flowering plants should also keep them coming through spring and summer. Maintaining a bird bath and a bird feeder should be especially effective! Other predators are sure to make a friendly visit to ecologically-balanced gardens, so it would be wise to cultivate a variety of native species.
