Organic gardeners have long struggled with soil pests and insects, as there is currently no organic chemical solution available to treat them. Wireworms, cutworms, and leatherjackets are particularly troublesome on newly cultivated land, as they can devour the roots of almost any plant.
To mitigate their impact, regular hoeing between plants can bring pests to the surface for birds to prey upon. Additionally, physical controls have proven effective against some of the most persistent pests, while encouraging natural predators can help to control their populations.
Fortunately, it is possible to control insects without resorting to chemical treatments. However, it is important to note that many insects are plant-specific, so targeted methods of control are necessary. The following discussion pertains to insects that can cause damage across a range of plants.
Physical treatment for soil pests and insects
Caterpillars are common pests in gardens, as the larvae of moths and butterflies often feed on plant leaves, stems, and even fruit. The cabbage family of plants is particularly susceptible to severe damage, as an infestation can strip crops of their foliage. If small clusters of eggs are detected, they should be removed directly from the plant. Caterpillars themselves can be easily picked off and disposed of in a jar of paraffin.
Leatherjackets, the larvae of the crane fly, are easily recognizable as white, fat, and unsightly creatures that can be found just below the soil surface, nibbling on plant roots. They may emerge on warm nights and eat through a plant’s stem at ground level. Leatherjackets can be controlled by squashing them when they are spotted during digging or hoeing. Ground beetles, which eat leatherjackets, can be encouraged by growing ground cover plants.
Wireworms are the larvae of click beetles, characterized by thin, shiny, yellowish skins. They often create small holes in potatoes and carrots, which can be mistaken for slug damage. To control wireworms, plant a row of wheat between crops at intervals over the plot in the first year or two of cultivating newly turned soil. The wireworms will be attracted to the wheat, which can then be removed and burned.
Alternatively, old potatoes or carrots can be used as traps for the wireworms, and an old cabbage stalk can be split and pushed into the ground near affected plants to attract and trap the pests. These traps should be periodically dug up and the wireworms removed and destroyed.
Cutworms are a type of garden pest that live just below the soil’s surface and feed on plants by cutting them off at soil level. They can be more troublesome than other pests like wireworms or leatherjackets.
If you find plants that have collapsed, you should search the soil just below the surface for cutworms. Hoe an area up to about one yard/meter away from the affected plant to expose the grubs. If you find any, you can get rid of them by squashing, burning, or drowning them in paraffin. You can also attract ground beetles to help control cutworms.
Aphids are one of the most common and problematic garden pests, including species such as greenfly and blackfly. They feed on plant sap and attack young growing tips, causing distortion. Aphids also excrete sticky honeydew that attracts sooty mold and can transmit virus diseases.
Fortunately, there are several predators, such as ladybugs and hoverflies, that eat aphids by the thousands. You can attract these helpful insects by planting French. You can also remove aphids by rubbing them off with your fingers or hosing them off with a powerful spray of water. If plants are badly infested, you can use insecticidal soap to control aphids.
Ants don’t usually harm growing plants directly, but they can be a problem when they carry aphids from one plant to another and protect them from predators like ladybugs and hoverfly larvae. This is because ants feed on the sticky honeydew that aphids produce.
Controlling aphids can often be enough to solve an ant problem. However, if ants become a nuisance, you can kill them with a mixture of equal parts powdered sugar and borax. Place the mixture on a piece of wood or stone near where there is ant activity, and cover it to protect it from rain. Ants are attracted to sweet things and will eat the bait. The poison will then be carried into the ant nest, and the entire colony will eventually be destroyed.
Slugs can be a problem in the garden, especially small brown or black slugs that live underground and are difficult to catch. The large slugs that live on fungi and dead organic matter are not harmful to plants.
One way to control slugs is to go out into the garden at night when they are feeding and pick them up and drop them into a jar of paraffin. This method can also reduce the numbers of underground-dwelling slugs. Another way is to surround vulnerable plants with lime, soot, or wood ash, which slugs avoid crawling through. You can also use plastic bottles or cans to protect young plants from slugs. Other helpful slug predators include hedgehogs, birds, frogs, and toads, which can be encouraged to visit the garden.
Earwigs can be a problem in ornamental gardens, as they tend to crawl to the tip of plants as they begin to bud and nibble on the embryo flower, as well as attacking leaves. While the damage may be minor, it can distort the flower and ruin the plant, especially chrysanthemums and dahlias.
To trap earwigs, place a flower pot upside down on top of a pole near the flower heads and fill it with dried grass or leaves. Earwigs will crawl into the pot during the day, and about once a week, the grass can be burned. If earwigs are still an issue, smear grease on the stems just below the blooms.
Flea beetles are small beetles that make hundreds of small “shot holes” in the leaves of seedlings, particularly those of the cabbage family. They can cause setbacks and even kill seedlings in bad growing years. To control flea beetles, coat one side of a piece of wood measuring about 1ft × 6in (30 × 15cm) with heavy grease, and pass it along the row of seedlings about 1–2in (2.5–5cm) above them. The beetles will jump up and stick to the grease.
Whiteflies are tiny insects that suck the sap of many greenhouse and outdoor plants. The ones that affect cabbages are especially persistent and resilient. To attract and trap whiteflies, hang up a yellow card or square of plastic coated with thin grease in the greenhouse. The whiteflies will be drawn to the card and stick to the grease. To prevent cabbage whiteflies from surviving outdoors in the winter, make sure there is no garden debris left around on which they can feed.
Other soil pests and insects
Seedlings and young plants can be severely damaged by woodlice, which emerge at night to nibble on roots, stems, and leaves. Millipedes, on the other hand, are small black insects with short legs that feed on roots beneath the soil surface and exacerbate damage caused by other pests like slugs. Similarly, snails can cause problems by eating seedlings and all parts of mature plants, just like slugs.
To combat these pests, it is important to keep the garden tidy, as they hide and breed under stones or garden debris during the day and only come out at night to feed. Regular and thorough cultivation of the soil will expose millipedes and woodlice to natural predators such as birds, hedgehogs, and ground beetles. Snails can be detected by their slime trails and removed from plants by hand, and dropped into a jar of paraffin or treated using one of the methods outlined for dealing with slugs.
Encouraging natural predators to combat soil pests and insects
An organic garden is a wonderful environment for all forms of wildlife. Unlike a chemically controlled garden, the natural balance in an organic garden ensures that there are predators that will feed on garden pests, making it a more conducive environment for all forms of life.
One simple rule to follow in order to distinguish between “friend” and “foe” in the garden is that pests are generally slow-moving, while predators are faster and more agile. By carefully observing this pattern, we can learn to let nature take its course and plan to attract helpful creatures into the garden. This approach often results in the eradication or lessening of the need for other forms of pest control.
Birds, for example, are usually considered to be somewhat of a garden pest in the productive garden. However, in fact, they do more good than harm. Birds eat numerous grubs, caterpillars, slugs, and aphids, and can be encouraged into the garden by incorporating food tables, bird baths, and nest boxes in your garden plan. Nesting requirements for different birds vary, and you can obtain more information from the National Audubon Society.
Ground beetles are another helpful creature in the garden, as they feed on eelworms, cutworms, leatherjackets, and other larvae and insect eggs. You can encourage them in your ornamental garden by keeping the ground covered, so that they have leaf cover or a mulch to hide under during the day. At night they will come out to feed on the pests. Use the closely planted deep bed system in the vegetable garden to keep the ground covered and grow a green-manure plant between crops.
Centipedes are fast-moving predators of many small insects and slugs. They are light brown with longer legs than millipedes. Like the black beetle, centipedes need ground cover to hide under during the day. At night, they will emerge in search of prey, even climbing the plants to reach it.
Frogs and toads
Frogs and toads are also excellent means of slug control, as they eat woodlice and other small insects. You should definitely try to encourage frogs and toads into the garden. A garden pond is perhaps the ideal environment for them, but they really only need the water for breeding purposes.
A family of hedgehogs is a great boon to any garden, as the creatures devour slugs, cutworms, woodlice, millipedes, and wireworms. While it is difficult to attract them into the garden, you can encourage them to stay if you have them. Hedgehogs will hide under piles of logs or hedges, so leave a saucer of milk and water or bread soaked in milk near the suspected hiding place.
Hoverflies are another helpful predator in the garden. It is the larvae of these creatures, which resemble “thin wasps,” that are very useful in the natural control of aphids. The adult flies lay their eggs directly in the aphid colonies, and the hatched young are voracious feeders. Hoverflies can be attracted into the garden by planting certain species of flowers such as marigolds (Tagetes and Calendula) and nasturtiums (Tropaeolum sp.).
Lacewings are another helpful predator in the garden. Again, it is the larvae that have an insatiable appetite for aphids. Adult lacewings lay their eggs on the undersides of leaves. Although they do not feed on flowers, they can be encouraged into the garden by varied planting.
Ladybugs, also known as ladybirds, are a common sight in gardens and agricultural fields. They are small, oval-shaped beetles that come in a variety of colors, including red, orange, and yellow. Ladybugs are popular among gardeners because they are voracious predators of aphids, which are notorious pests that feed on the sap of plants and transmit viruses.
Ladybugs are not only effective at controlling aphids but also mites, mealybugs, scale insects, and other soft-bodied insects. In fact, a single ladybug can consume up to 5,000 aphids in its lifetime! Ladybugs are attracted to plants that have a lot of nectar and pollen, such as marigolds, fennel, and dill. By planting these types of plants in your garden, you can encourage ladybugs to stick around and help keep your garden pest-free.
Maintaining a healthy and diverse ecosystem in the garden can help promote natural pest control by attracting helpful predators such as birds, ground beetles, centipedes, frogs, toads, hedgehogs, hoverflies, lacewings, and ladybugs.
By understanding the natural balance between pests and predators, gardeners can reduce or eliminate the need for chemical pesticides, which can harm the environment and beneficial insects.
By incorporating various techniques such as companion planting, crop rotation, and ground cover, gardeners can create a sustainable and thriving garden that supports both plant growth and wildlife diversity.