How to identify common garden pests, and keep them away
It's helpful to know how to identify the caterpillars, aphids, and other pests that can destroy a garden—like this cross-striped cabbage worm—so you can keep them away. Photo by Away to Garden
To protect your garden against pests it helps to know who they are, because not all bugs and insects are bad. Wasps, moths, and flies can pollinate your plants, and spiders eat up many of the pests that can spoil a garden.
To help you sort it all out, I've put together a quick intro to the pests you don't want hanging around, along with tips on how to keep them away. For specific guidance on how to treat pests with insecticidal soap, Neem oil, and other organic repellants, read How to manage pests organically.
Suckers
These bugs have piercing mouthparts that break through the surface of leaves to suck out sap or plant tissue. Many of the most destructive garden pests fall into this category so keep an eye out for them. Punching tiny holes through the protective layer of leaves also leaves plants open to disease. Suckers can even transmit harmful diseases to plants, much in the way a mosquito can infect our blood with malaria.
It can be hard to detect damage from sucking insects before they become a real problem. One sign they've arrived is the appearance of sticky leaves. Suckers, who are messy eaters, tend to leave syrupy drippings all over the leaves. Eventually the sugar residue grows sooty mold which looks just like somebody smeared ash all over your gorgeous plants.
Symptoms can also mimic drought stress, making it a challenge to know if you are dealing with pests or a lack of water. Another sign of trouble is yellowish, dappled leaves that eventually curl up and turn grey or black.
Aphids: These minute, pear-shaped bugs come in red, yellow, green, and black. They are easily identified by long string-like antennae protruding from their heads. Look for aphids on the stems of new growth or under leaves. In low numbers they're not harmful to plants. But large infestations will stress your plants, making them prone to other bug attacks or diseases.
Treatment: Wash leaves with insecticidal soap, attract beneficial bugs (ladybugs, the green lacewing, the syrphid fly and the parasitic wasp), spray off with a hose.
Leafhoppers: More than 20,000 different kinds of leafhoppers are sucking the life from plants all over the world. A common one, the potato leafhopper, is a tiny lime green bug that hides underneath plant leaves. Leafhoppers generally move in sideways steps so if you’re not sure what you’re looking at watch how it moves. To find them check the underside of leaves by gently shaking your plant to see if they leap off in surprise.
Treatment: Use floating row covers, apply diatomaceous earth (DE), wash leaves with insecticidal soap.
Thrips: Young thrips look a lot like potato leafhoppers to the untrained eye. A thrip is a tiny lime green bug that moves quickly. Take out a hand lens to catch a glimpse of the bug to see if it has feathery wings. Adult thrips turn a dark brown or black. Since they only get as thick as a sewing needle they appear as tiny black slivers on plants.
Treatment: Use blue sticky traps, treat leaves with neem oil or insecticidal soap.
White flies: These tiny moth-like bugs with powdery white wings usually attack in large numbers. They like to gather at the tops of plants or near the ends of stems. If you can’t see them try shaking the plants and watching for a cloud of white flies.
Treatment: Use yellow sticky traps, neem oil, or horticultural oils.
Scale: These weird bugs are immobile and look like small oval bumps rather than insects. Their look comes from a protective covering that they produce while feeding to stave off predators.
Treatment: Attract beneficial insects (ladybugs, lacewings), apply neem oil or insecticidal soap to leaves.
Spider mites: Looking like miniature ticks, these pest can wreak havoc in the garden. They are so small you’ll need a hand lens to spot the colonies on the bottoms of leaves. You can also look for very fine webbing left behind in leaves after they devour it.
Treatment: Dust plants if possible, apply neem oil or insecticidal soap to leaves.
Defoliators
Pests like beetles, caterpillars and slugs are another nuisance. While not as bad as suckers, defoliators harm plants by eating away at leaves and stems. Some eat small holes while others consume entire leaves, leaving nothing but the veins behind. Big infestations can destroy so many leaves your plants won’t be able to photosynthesize.
Caterpillars are the larval stage of flying insects, like moths and flies. Adults lay a swath of eggs on the underside of leaves so when they hatch there's plenty of food for the larvae to enjoy. Some caterpillars, like the cabbage looper can eat up to three times their own body weight. They also like to build shelter around them as they feed, meticulously folding or rolling leaf edges around them for protection.
Treatment: Apply Bacillus thuringiensis (Bt), handpick them off, protect leaves with row covers, attract beneficial insects (Trichogramma wasps) to destroy eggs.
Beetles can be a real headache for gardeners. They have the ability to take out a whole crop if there are enough of them. Washing leaves with insecticidal soap can effectively repel them.
Beetles: Over 12,000 kinds of beetles live in the United States, and many of them like to feast on plants. Japanese beetles will eat entire plant leaves, leaving behind only the stem, while flea beetles attack your plant by leaving hundreds of tiny holes.
Treatment: Handpick them off; protect plants with row covers; apply insecticidal soap, garlic-pepper spray, and neem oil.
Slugs and snails: Slugs and snails are not true bugs; they’re actually members of the mollusk family. Slimy and slow, these pests are most active at night and thrive in cool, damp and shady areas where they can’t dry out. These squishy invertebrates leave almost nothing unharmed as they chew large holes in leaves and destroy tender seedlings. They love to munch on ripening fruits and vegetables, causing them to prematurely rot.
Look for their slimy trail, a dead give-away they’ve been roaming through the garden. Watering in the morning can reduce slug numbers because the plants have a chance to dry out before night fall.
Treatment: Handpick them off plants, use iron phosphate slug bait or diatomaceous earth (DE), and water plants in the morning.
Large pests
Animals like deer, rabbits, and birds can cause a lot of damage in no time at all. Moles, voles, chipmunks, raccoons are also pests who always seem to know exactly when it’s time to harvest, often beating you to the punch. It’s such a frustrating feeling heading out into the garden to harvest lunch only to find it was already eaten without you.
Treatment: Apply essential oils or urine; install fake predators like owls or falcons; use flash tape, motion sensor sprinklers, fencing, humane traps, or Plantskydd.
NOTE: Here's additional information on how to repel pests using insecticidal soap, neem oil, Plantskydd, and other treatment options.
Acadia Tucker is a climate activist and regenerative farmer in Maine. She has written three books on how to grow your own food organically, using regenerative methods. All are available in our bookstore.