Faced with a pest problem? Learn a three-tiered approach to natural garden pest control: attract beneficial insects, employ effective physical pest controls such as handpicking and row covers, and use organic pesticides if needed.
Place birdhouses and simple water features around your garden to invite in natural predators. Keep chickens near your garden to feed them handpicked pests. They can also work over beds at season’s end. Keep out slugs by laying out copper stripping and use row cover to protect cabbage-family crops.
Illustration by Linda Cook
An abundance of buzzing, hopping, fluttering and crawling insects is a trademark of any healthy organic garden. This diversity means insects that might feed on your crops are likely to be kept in check by their enemies. In small numbers, pests simply provide food for birds and beneficial insects, and if your soil and crops are healthy, plants fend off the pressure easily. Only when pest populations become excessive do gardeners need to step in to restore balance to keep their gardens thriving.
A good overarching mantra to guide you in your natural garden pest control efforts can be summed up in two words: Look closely. Examine your plants regularly, noting what kinds of insects you see. Observe whether you see just a few of a particular kind of insect or whether populations are growing, and look up pictures of what you see so you know which are beneficial and which are detrimental. (For pictures of and detailed information about beneficial and pest insects, see our Organic Pest Control Series.)
Refer to this glossary to preemptively ward off pests and, if problems do crop up, to target each complication with the best organic pest control solutions. We’ve separated this glossary into sections that present a three-pronged system of organic pest control: First, attract a diversity of beneficial insects by interplanting flowers and herbs — especially those that produce nectar from numerous small florets, such as mints and sweet alyssum. Second, put a variety of physical controls in place when pests get out of check or are known to be troublesome in your area (see the Top 15 Worst Garden Pests chart). Last, if needed, bring in organic insecticide reinforcements. The products listed in this glossary all have been approved by the U.S. National Organic Program.
The following insects feed on other insects, helping prevent pest species from doing more than minor damage to your crops.
Assassin bug. These 1-inch-long predatory bugs have shield-shaped backs and are active pest hunters. Larvae and adults feed on aphids, caterpillars, Colorado potato beetles, insect eggs and more. Assassin bugs are among the few natural predators that help control Mexican bean beetles.
Braconid wasp. North America is home to nearly 2,000 species of these non-stinging wasps. Adults are less than a half-inch long, and they lay eggs inside or on host insects; the maggot-like larvae feed on their prey from inside. Braconids lay eggs on numerous pests, such as aphids, caterpillars (including cabbageworms and tomato hornworms), and leaf miners.
Ground beetle. These beneficial insects live in the soil beneath mulches, around compost piles, and in the sheltered areas below perennial plants. Some create vertical tunnels that they use to ambush and trap prey, but most ground beetles wander about aboveground, foraging for food at night. They dine on asparagus beetles, cabbageworms, Colorado potato beetles, corn earworms, cutworms and slugs.
Hover fly (aka syrphid fly). Black-and-yellow-striped hover fly adults resemble yellow jackets but are harmless to humans. Larvae are petite, tapered maggots that crawl over foliage to feed on small insects. They are aphid-eating machines and also devour mealybugs, mites, thrips, scale insects, and small caterpillars, such as cabbageworms.
Lacewing (aka aphid lion). Lacewing larvae prey on aphids, cabbageworms, caterpillar eggs, whiteflies and more. They feed for about a month, in which time each larva consumes about 600 aphids. Remove row covers from plants during evening hours so lacewings can check them for pests. Do not use pesticides when lacewings are active, which happens early in the gardening season compared with most natural insect predators.
Lady beetle (aka ladybug). Lady beetle larvae and adults eat aphids, small caterpillars and insect eggs. A few species specialize in eating mealybugs, mites, scale insects and even powdery mildew. If you see adult lady beetles on a plant, look in the foliage for clusters of yellow-orange eggs, which will often be near an aphid colony. Dark-colored larvae, which resemble miniature alligators, will hatch in about a week and consume several aphids per day.
Minute pirate bug. Less than a quarter-inch long, this compact predator controls corn earworms early in the worms’ life cycle. Minute pirate bugs also feed on aphids, thrips and whiteflies.
Praying mantis. The largest insect you’re likely to see in your garden, this predatory species is always on the prowl, eating any other insect that moves, including crop-munching grasshoppers.
Soldier beetle (aka leatherwing beetle). You’ll spy elongated, half-inch-long soldier beetles among flowers or in thick vegetation. In some areas, the larvae are key predators of grasshopper eggs, so attracting soldier beetles can provide grasshopper control. Soldier beetle larvae eat moths, several insects, and the eggs and larvae of other beetles. Adults feed on aphids, caterpillars and other soft-bodied insects. Goldenrods, single-flowered marigolds and members of the daisy family are soldier-beetle magnets.
Spider. These eight-legged critters are probably the most abundant pest predators on your property. Any garden will likely already host several dozen types of spiders, and the most common garden spiders don’t spin webs. For example, wolf spiders live in shallow underground burrows, wandering the soil’s surface by night, or simply waiting by their burrow for unsuspecting prey. Perennial herbs that grow into lush bushes often make top-notch spider conservatories, and biodegradable mulches, such as straw and grass clippings, create an ideal habitat for advantageous wolf spiders. (Note that poisonous spiders don’t generally favor gardens.)
Tachinid fly. Tachinid flies are gruesome parasites that glue their eggs onto an insect so that, when the egg hatches, the maggot can consume its host as food. Some species lay eggs on foliage that’s food for insects, and then the eggs hatch in the insects’ innards. Or, the flies inject eggs into another insect’s body with a sharp ovipositor. Garden pests controlled by tachinid flies include armyworms, cabbageworms, cutworms, grasshoppers, Japanese beetles, leaf rollers and squash bugs. Attract tachinid flies by growing plants that bear umbels of tiny flowers. Buckwheat, carrots, cilantro, dill, Queen Anne’s lace and sweet clover are among the crops that fit this bill.
Trichogramma wasp. These gnat-sized wasps lay their eggs inside the eggs of other insects, where the young trichogramma then develop as internal parasites, breaking the host’s life cycle. Common hosts include eggs of cabbageworms, codling moths and European corn borers. Trichogramma wasps are too tiny to observe in the garden; however, scientists have found that flower nectar from buckwheat and sweet alyssum enhanced wasp reproduction in lab experiments.
Wasp (stinging types). Wasps can be great garden allies because they consume huge numbers of leaf-eating caterpillars and irritating flies, which they feed to their growing larvae. Take caution if yellow jackets or hornets show up, and mark wasp nests so you can avoid disturbing them. Paper wasps are less aggressive than yellow jackets or hornets, and are happy to nest in bottomless birdhouses placed around the garden.
Cleanup. Practice good garden sanitation for certain crops at season’s end to disrupt the life cycle of pests that feed on those crops. After your cucumber and squash plants are spent, remove plant debris from the garden and chop it into small pieces before composting it. Do the same with asparagus, which can host asparagus beetles, and with broccoli and cabbage stumps, which can harbor cabbage aphids. If you have problems with pests that overwinter as adults, mow down any weedy areas in fall.
Copper strips. Slugs receive an unpleasant electrical jolt if they crawl over copper. Garden centers sell copper stripping that you can place around particular crops or even use to encircle entire garden beds to keep slugs out. The strips should be at least a few inches wide so slugs can’t traverse them unscathed.
Cutworm collars. Push cylindrical “collars” — which can be made from small cans, yogurt cups or toilet paper rolls — into the soil around tomato, pepper and other transplants to protect the young plants from cutworm damage.
Handpicking. Ultra-low-tech but effective for organic gardeners, handpicking is just what it sounds like: Spot pests and squish them or brush them into a pail of soapy water (or collect them for your chickens). Keeping a close eye on your crops and knowing how to identify pests are the keys to this method. Pests that haven’t become overwhelming in number and are big enough to spot easily, such as slugs, tomato hornworms and other worm-type pests, are prime candidates for handpicking.
Poultry. Insect-munching fowl will devour practically any insect that moves, including ticks, grasshoppers, Colorado potato beetles, slugs and more. Ducks are reportedly sharp slug-spotters, whether you let them work over the garden in spring and fall or enlist a pair as your assistants throughout the season. Chickens work best in winter, because their scratching can damage crops during the growing season. (See Chickens in the Garden: Organic Pest Control for reader reports about how to most effectively control pests with poultry.)
Row covers. A lightweight row cover or tulle netting will keep some crops pest-free. Cover your cabbage patch in this way, along with other cabbage-family crops, to keep cabbageworm moths from laying eggs on your plants. Use hoops or blunt stakes to hold up the covers. Remove covers after crops, such as squash, begin to flower, so that pollinators can reach the flowers.
Vacuum. Some gardeners report successfully controlling squash bugs and other pests by sucking them up with a shop vacuum. Got poultry? Empty the vacuum bag into their pen and everybody wins — except the pests, of course.
Yellow sticky traps. Hang flat, sticky traps near cucumber plants to catch cucumber beetles. To snare flea beetles, place traps near eggplants and other crops suffering from flea beetle pressure. These pests are attracted to the color of the traps and will get caught in the goo.
Bt (Bacillus thuringiensis). This naturally occurring bacterium kills caterpillars when they eat leaves that have been sprayed with it. Armyworms, cabbageworms, corn earworms, diamondback moths, grape leaf rollers, melon worms, tomato fruitworms, tomato hornworms, and various webworms and budworms are candidates for Bt treatment. Butterfly larvae may also be killed by Bt, so don’t use it on butterfly host plants, such as parsley. Additional strains of Bt include one that kills mosquito larvae and one that is toxic to Colorado potato beetle larvae. Sunlight degrades Bt after a few hours, so apply it late in the day. Reapply after heavy rain.
Diatomaceous earth (DE). A powder made from fossilized remains of aquatic organisms called “diatoms,” DE has sharp edges that cut into insects’ bodies and cause them to die of dehydration. DE is less effective when wet, yet can still be used in the garden to make life difficult for flea beetles and newly emerged cutworms and Japanese beetles. In dry weather, DE spread beneath plants will repel slugs. Lightly sprinkle dry DE on the soil’s surface where Japanese beetles, slugs, or other pests will come into direct contact with the dry particles. Renew after rain or dew.
Horticultural oils. When applied directly to pests, horticultural oils interfere with respiration, causing insects to suffocate and die. These oils help control aphids, whiteflies and other pests, but can also kill beneficial mites and injure the leaves of some plants. Frequent use can reduce yields even when the pest is under control. Best applied in cool weather, horticultural oils are valuable allies in organic orchards, where they can control pests that overwinter in bark crevices.
Insecticidal soap. Fatty acids in insecticidal soaps break down the protective cuticles of soft-bodied pests, such as aphids, which will then quickly become dehydrated and die. Soap sprays have no residual effect and only kill insects that are sprayed directly. Thoroughly wet both sides of leaves and the insides of all crevices. Repeat applications may be needed every week as new aphids or whiteflies hatch and form colonies. To make soap sprays at home, mix 1 tablespoon of dishwashing liquid per quart of water. Purchased insecticidal soaps are purer, however, and less likely to injure foliage. Frequent soap sprays may reduce the yields of some crops. Use soft or rainwater when diluting soap concentrates.
Iron phosphate slug bait. Sprinkle slug-bait granules evenly throughout your garden beds, and slugs will eat it instead of your plants, then crawl off to die. The bait is nontoxic to pets and humans. Sluggo is a popular brand of this type of bait.
Neem. When applied to insects and the plants they eat, neem oil, which is derived from an Asian tree, causes many insects to feed less, grow more slowly, molt less and stop laying eggs. Neem works best on young insects, particularly those that grow rapidly, such as Colorado potato beetles, Mexican bean beetles and squash bugs. Neem can also control aphids and leaf-eating caterpillars.
Pyrethrum. One of the oldest known pesticides, fast-acting pyrethrum is also the strongest insecticide allowed under U.S. National Organic Standards, so use it only after you’ve exhausted other methods. Insects, including beneficials, typically become paralyzed as soon as they come into contact with pyrethrum, which is made from the dried flowers of the daisy Tanacetum cinerariifolium. Aphids, armyworms, Colorado potato beetles, cucumber beetles, cutworms, leafhoppers, squash bugs and whiteflies can often be brought under control with pyrethrum.
Spinosad. A biological pesticide, spinosad is derived from the bacterium Saccharopolyspora spinosa, which produces a substance that works as a neurotoxin in many (but not all) insects. Susceptible insect species become excited to the point of exhaustion, stop eating, and die within two days. Spinosad controls all types of caterpillars, Colorado potato beetle larvae and blister beetles, and works best on pests that consume a lot of leaf tissue.
Need to deal with garden pests? Check out the Top 15 Worst Garden Pests chart.
Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on Google+.
Shelley Stonebrook is MOTHER EARTH NEWS magazine’s main gardening editor. She’s passionate about growing healthy, sustainable food and also runs Stonegrass Farms Soap Co. in her spare time. Follow her on Twitter and Pinterest.