Quick Guide to Getting Rid of Common Pests
The following list of vegetable, flower, tree, shrub, and fruit pests includes the worst offenders. Many more insects cause damage, of course, and you can get more information about the ones to watch out for from your local extension office:
- Aphids: These pear-shaped pests, shown in Figure 8-1, pierce holes in plant tissue and suck the juices. Their sizes range up to V» inch, and color varies depending on the species, from black to green, red, or even translucent. Aphids leave behind sticky sap droppings called honeydew that attract ants and may turn black if covered with sooty mold. Aphids can proliferate quickly on weakened plants and tend to congregate on the newest leaves and buds. Blast them off with a hose; control them with beneficial green lacewings, ladybugs, or sticky yellow traps; or spray them with insecticidal soap.
- Apple maggots: Slightly smaller than houseflies, these pests spend the winter in soil and then appear in June or July, mainly in northern climates, to begin laying eggs in apples, crabapples, plums, and other fruits. Maggots hatch and tunnel through the fruit, ruining it (see Figure 8-2). Rake up and dispose of infested fruit in the fall before the maggots emerge and become established in the soil for the winter. Trap adult flies with red, apple-like spheres coated with sticky goo (refer to "Apple maggot traps," earlier in this chapter) and baited with a special apple-scented lure. Begin trapping three weeks after the petals begin falling from the blossoms in spring and continue through August, cleaning and refreshing the sticky stuff as needed. Use one to two traps in young or small, 6- to 8-foot-high fruit trees, and six traps in mature 10- to 25-foot trees. Apply a spinosad-based insecticide.
- Ataenius spretulus: These M-inch-long black beetles lay eggs in turfgrass in the spring. The eggs hatch into small white grubs, which feed on grass roots until midsummer. After pupating, new adults emerge from the soil and mate; then they prepare for winter by burrowing an inch or so deep into the soil. Discourage the pest by reducing lawn thatch and encouraging predatory and parasitic beneficial insects.
- Bagworms: Bagworms are the larval stages of moths. After hatching in late spring, bagworm caterpillars use pieces of plant debris to construct dangling 1- to 2-inch-long, baglike structures for themselves. The small caterpillars feed on the leaves and twigs of many trees and shrubs, especially arborvitae and juniper. Cut the bags loose, removing the silk that wraps around the stem, and destroy them. Spray with Bacillus thuringi-ensis (Bt) or a spinosad-based insecticide in early spring, or trap adults with sticky pheromone traps.
✓ Bean leaf beetles: Adult beetles, shown in Figure 8-3, chew large holes in bean leaves, and the larvae attack the roots. Control by covering plants with row-cover fabric. Spray with the organic pesticide neem as a last resort.
✓ Billbugs: The adult beetles have long snouts and eat turfgrass leaves, while the grubs consume the grass roots and lower stems. They're especially fond of zoysia and Bermuda grasses. Control by planting tall fescue and perennial ryegrass varieties that contain endophytes.
Don't use these grasses where horses, cattle, and sheep will graze, because endophytes produce a toxin that affects animals as well as insect pests.
- Black vine weevils: Both adults and larvae of this snout-nosed beetle species damage fruit and ornamental plants. The K-inch-long black adults emerge from the soil in early summer and lay eggs near the soil on host plants. When the eggs hatch, the larvae burrow into the soil and eat the roots. Meanwhile, the adults eat crescent-shaped notches in the leaves. Control by covering crops with floating row-cover fabric to screen out adults or by knocking the adults off the plants onto a drop-cloth in the evening. Use beneficial nematodes for the larval and pupal stages.
- Borers: Some beetle and moth larvae tunnel into the wood, canes, and stems of raspberries, roses, rhododendrons, squash, fruit trees, and other ornamental trees and shrubs, as shown in Figure 8-4. The tunneling weakens the plant and makes it more disease-prone, and can cut off sap circulation, causing wilting and twig or cane death. Prevent borers by choosing plant species that are less susceptible, wrapping the trunks of young trees to prevent sunburn or other wounds where borers can attack, and covering susceptible vegetable crops with floating row-cover fabric. Watch for signs of damage, including dead bark, sawdust piles, dead or wilted canes and limbs, and poor performance. Control by slitting open affected stems and killing the larvae or pruning off and destroying stems. If you find borers or bark beetles, cut off and destroy the severely infested limbs, inject beneficial nematodes into the remaining borer holes, and remove dead or dying trees and plants.
- Cabbage loopers: The 1-inch-long, gray, adult moths lay eggs on cabbages, broccoli, cauliflower, and similar types of crops in late spring to early summer. The bright green caterpillars have white stripes down each side of their bodies and move with a looping motion. Control by handpick-ing the caterpillars, encouraging beneficial wasps, and spraying Bt.
- Chinch bugs: Both the immature nymphs and the black-and-white, >6-inch-long, winged, adult bugs cause significant damage to lawns and grain crops by sucking the juice from grasses. Irregular patches of lawn turn brown, and you may detect a foul odor from crushed bugs when you walk over the affected areas. Control by planting endophyte-con-taining grasses and encouraging beneficial predator insects by allowing clover to grow in your lawn.
Peach tree borer, 1" long
Peach tree borer, 1" long
Stem-boring insects. Shot hole borer
Pacific flathead borer
Stem-boring insects. Shot hole borer
- Codling moths: This K-inch-long brown moth lays its eggs on the leaves and twigs of apples and other fruits, starting when the trees' flower petals begin falling in the spring and continuing through the summer. When the caterpillars hatch, they tunnel through the center of the fruit, as shown in Figure 8-5. Control adult codling moths by trapping, killing, or confusing them with sticky pheromone-baited traps. Immature larvae spend the winter under the loose bark of fruit trees and in fallen apples. Spray trees with horticultural oil in early spring before the leaves emerge to smother the larvae. You can also trap the larvae by wrapping corrugated cardboard around the tree trunks in summer and then destroying it after the insects crawl inside. Monitor and replace every one to two weeks.
- Colorado potato beetles: The yellow- and black-striped adults, shown in Figure 8-6, emerge from the soil in early summer, mate, and lay orange eggs on the undersides of potato-family leaves, such as potato, eggplant, tomato, tomatillo, and nightshade. Both adults and larvae defoliate potato-family crops quickly. The reddish grubs devour the plant leaves and then develop into beetles, which lay a second generation of eggs later in the summer. The adults spend the winter in the soil and in plant debris. Control by encouraging spiders, lady beetles, predatory stinkbugs, and tachinid flies. Cover plants by applying a floating row cover or straw mulch, handpicking adults, crushing egg clusters, and spraying Bt san diego or a spinosad-based insecticide on very young grubs.
- Corn earworms and tomato fruitworms: This caterpillar is one and the same critter, but its name changes depending on the crop it's damaging. The adult moths emerge in spring to lay their eggs on plant leaves and corn ears. The caterpillars burrow into the fruit or eat the leaves for up to a month before dropping to the soil to pupate. Control in corn by choosing resistant varieties with tight husks on their ears or by applying soybean oil mixed with Bt or spinosad to the corn silks. Handpick from other fruits and vegetables, encourage beneficial bugs and wasps, or spray with neem. In warm regions, the pupae overwinter in the soil; light tilling exposes them to predators. In colder regions, the moths migrate in fall.
- Cucumber beetles: Striped and spotted cucumber beetle species, shown in Figure 8-7, cause significant damage by chewing large holes in the leaves, roots, and fruit of vegetables such as squash, corn, beans, and peas. They can also carry viral and bacterial wilt diseases, spreading the diseases throughout your garden. Both adults and larvae feed on plants. Control by covering plants with row covers until they flower to prevent adults from laying eggs. Remove plant residue from the garden to eliminate winter hiding places. Use beneficial nematodes to control grubs in the soil; use a particle film barrier like Surround WP to confuse the adults and discourage feeding.
Colorado potato beetle adults and larvae.
Colorado potato beetle adults and larvae.
Striped and spotted cucumber beetles.
Striped and spotted cucumber beetles.
- Cutworms and armyworms: The 1- to 2-inch-long cutworm caterpillars, shown in Figure 8-8, chew through the stems of young plants at night, killing them, and then spend the day curled in the soil nearby. Armyworms also feed at night, usually in early summer, stripping the leaves from grasses, grains, and vegetable crops. Control by picking the caterpillars from the soil near decimated seedlings and spraying Bt or spinosad to kill caterpillars. Spray horticultural oil in midsummer to kill the eggs on host plants. Remove plant debris from gardens to prevent overwintering by adults. Wrap the stems of young vegetable plants with 2- to 3-inch-wide strips of newspaper so that half the paper extends below the soil surface.
- Flea beetles: The highly mobile, shiny blackish beetles are only Xo inch long, but they tend to feed in large groups, skeletonizing leaves in a few days' time. Adults emerge in spring and do most of their damage by midsummer. Eggs, laid in the soil, hatch into larvae that eat plant roots until late summer. Control by covering vegetables and susceptible flowering plants with row-cover fabric or delaying plantings until the beetles subside. Beneficial nematodes attack the grubs. You can also vacuum them up with a small handheld vacuum cleaner early in the morning, while they're still sluggish. A particle film barrier like Surround WP may discourage feeding.
- Gypsy moths: The adult moths lay masses of eggs under a fuzzy covering on trees and other surfaces in autumn. The caterpillars are 2 inches long, and are gray with brown hairs and distinctive red and blue spots (see Figure 8-9). They emerge in spring to eat the foliage on several species of shade trees, including oaks. This pest spreads across the country as the caterpillars and egg clusters hitchhike on cars, campers, trains, and trucks. Catch caterpillars as they attempt to crawl up tree trunks by using a sticky pest barrier wrapped around the tree. Spray the caterpillars with Bt, spinosad, or neem. If the pests are severely damaging any trees that are too tall for you to treat yourself, call an arborist for help.
- Imported cabbage moths: The white moths have a distinctive black dot on each wing. They flutter around your garden, laying yellow eggs on the undersides of leaves of cabbage, broccoli, and other cole crops in the spring and early summer. The fuzzy green caterpillars hatch and quickly begin feeding on leaves and developing flower buds, leaving piles of green excrement. Control by covering crops with floating row covers or by handpicking and crushing eggs and caterpillars. Spray with Bt or spinosad, if necessary. Yellow sticky traps attract the adults.
- Japanese beetles: Found mostly east of the Mississippi River, the fat, white, C-shaped, /4-inch-long larvae live in the soil under turf, where they consume grass roots from early spring to early summer. The adults — K-inch-long, metallic blue-green beetles with coppery backs — emerge from the soil in midsummer and attack plants with gusto, stripping leaves, buds, and flowers. Inspect your garden in the evening or early morning for the beetles, shown in Figure 8-10, knocking them off plants into a can or bucket of soapy water. To control the larvae, treat your lawn with milky spore disease, which takes several years to spread through the lawn, or with beneficial nematodes, a quicker-acting helper. Neem sprays may discourage feeding.
- Lace bugs: These //»-inch-long insects suck the sap out of the undersides of foliage, giving the leaves a whitish or yellow blotchy appearance. Look under the leaves for their sticky brown droppings. Ornamental plants including firethorn, mountain laurel, cotoneaster, and rhododendron are vulnerable, as well as vegetables and flowers. Hose off insects or spray with horticultural spray oil to suffocate the pests, concentrating on the undersides of the leaves. Use insecticidal soap or neem on heavy infestations.
- Leaf miners and sawflies: The larvae of tiny sawflies, moths, beetles, and flies, these pests tunnel through the leaves of trees, shrubs, flowers, and vegetable plants (honeysuckle, tomato, holly, pine, boxwood, birch, and lilac), leaving discolored patches on the foliage. Control by planting vulnerable crops in a new place each year and covering with row-cover fabric in spring. Remove and destroy infested leaves, shown in Figure 8-11, and rake up any that fall. Eliminate host weeds, especially lamb's-quarter and dock, but encourage parasitic wasps with carrot-family plants. Spray with neem in spring, when adults begin to lay eggs. Leaf-miner damage is mostly cosmetic.
- Leafhoppers: These small, wedge-shaped adults jump from plant to plant, especially when disturbed. The adults and immature nymphs suck plant juices, distorting plant growth and spreading plant diseases. Many beneficial insects prey on and parasitize the nymphs. You can also try spraying plants with strong blasts of water to dislodge the immature insects. Spray neem if necessary.
- Nematodes: Plant-damaging nematodes are microscopic, wormlike creatures that live in the soil. (They're different species from the beneficial parasitic nematodes.) They usually attack plant roots, causing abnormal growths and decreasing the plant's ability to take up water and nutrients. Some nematodes also attack stems and leaves. Control by rotating vegetable crops, and avoid planting susceptible crops in the same place each year. Solarizing the soil — covering it with clear plastic and letting it bake in the sun — also provides some control. Planting certain types of marigolds can discourage nematodes. The marigold (Tagetes patula) variety called Single Gold, also sold as Nema-gone, has proved most effective in Dutch trials. Many nematodes are beneficial, however, and actually attack the harmful kinds.
- Oriental fruit moths: These small, slim moths produce several generations of larvae each year in the North and as many as seven generations in the South. In the spring, the first larvae tunnel into the new twigs of fruit trees, causing wilting and twig death. The midsummer generations burrow into the fruit, leaving sticky residue on the surface. Late-summer larvae tunnel into the stem ends of the fruit, leaving no visible signs but destroying the inside of the fruit. Larvae spend the winter in tiny cocoons on tree bark and surrounding plant debris. To control, work the soil shallowly around infested trees in early spring to kill the larvae, and spray trees with horticultural oil spray. Use pheromone traps to catch adult males and disrupt mating. Attract parasitic wasps and flies with flowering plants nearby.
✓ Plum curculios: Occurring east of the Rocky Mountains, these X-inch-long weevils, shown in Figure 8-12, cause significant damage to apple, pear, and cherry fruit. The female beetles make crescent-shaped cuts in young fruit right after the petals fall from the flowers and then lay their eggs in the wound. When the grubs hatch, they eat through the fruit, causing it to drop from the tree. The larvae pupate in the soil and emerge as new adults in mid- to late summer. To control the adult beetles, spread out a tarp or old sheet underneath the tree, shake the tree to knock the beetles off, and then step on them. Rake up and destroy fallen fruit, which may contain larvae. Keep plant debris out of orchards to eliminate hiding places for overwintering adults. If you happen to have a flock of chickens, as I do, let them forage for insects under the trees.
- Root maggots: Small flies of several species lay eggs in the soil near host plants or on the base of the plant. When the maggots hatch, they burrow into the roots, killing or stunting the plant. Onions, leeks, vegetables in the cabbage family, radishes, and carrots are common targets. Onion maggots can kill significant numbers of onion seedlings, especially in cool, wet weather. Control by covering susceptible crops with floating row-cover fabric or apply beneficial nematodes.
- Rose slugs: The X-inch-long sawfly larvae and adults eat the undersides of rose leaves and related plants in spring and early summer, quickly stripping them to skeletons. Handpick small infestations, or spray with insecticidal soap or horticultural oil.
- Sawflies: The caterpillar-like larvae of the sawfly, shown in Figure 8-13, hatch in early spring and devour the foliage of needle-bearing evergreens, especially pine, hemlock, and spruce. They pupate in the soil, emerging as adults in the fall. Adults lay eggs in cracks in tree bark. Many natural predators eat the larvae and pupae. Control by spreading a dropcloth under infested trees and collecting the larvae as they drop to the ground in late summer. Spray trees with horticultural oil in early spring to smother eggs and newly hatched larvae. Avoid using oil on blue spruces, however, because it will permanently discolor the foliage.
- Scales: Adult scale insects, shown in Figure 8-14, may have a hard or soft shell-like exterior that resembles bumps on plant stems and leaves. These pests suck plant sap and can weaken and even kill plants if present in large numbers. Many species secrete sticky honeydew that encourages fungus. Control is difficult on large trees and shrubs; your best bet is to release and encourage predatory beetles and wasps. Remove and destroy badly infested stems, and spray with horticultural oil. Indoors or on small plants, clean off light infestations with a cotton ball soaked in soapy water.
- Snails and slugs: These pests feed on the tender leaves of many ornamental, fruiting, and vegetable plants during the cool of night or in rainy weather. Sometimes they're hard to spot: All you see are the slime trails they leave behind and the holes they chew in leaves and fruit. They proliferate in damp areas, hiding and breeding under rocks, mulch, and other garden debris. Control by placing boards, cabbage leaves, or other hiding places in the garden. In the early morning, lift the traps and destroy the slugs by sprinkling with a 50/50 mix of ammonia and water. Shallow pans of beer also attract and drown these pests. Surround plants and gardens with copper barriers — metal strips that seem to shock slugs if they attempt to crawl across them. Diatomaceous earth and wood ash also deter them but must be refreshed periodically. Look for nontoxic baits that contain iron phosphate.
- Spider mites: These tiny arachnids, shown in Figure 8-15, are almost microscopic, but when they appear in large numbers, you can begin to see the fine webs that they weave. Use a magnifying glass to identify them. They suck plant sap, weakening plants and causing leaf discoloration. They're especially active in arid conditions. Favorite hosts include fruit trees, miniature roses, citrus, pines, and houseplants. To control, wash plants with a strong blast of water, use dormant oil in early spring, or use light horticultural oil or insecticidal soap in summer. Encourage beneficial insects, many of which prey on spider mites.
- Spruce budworms: These caterpillars cause significant damage to spruce and fir forests throughout North America and can severely disfigure and kill landscape trees, too. In midsummer, moths lay eggs, which hatch into small, orange-yellow to brownish caterpillars. The caterpillars hibernate until the following spring when they emerge to eat the mature and newly developing needles. Symptoms include dead shoots and chewed needles and cones. Control the pest by spraying with Bt in late summer as the newly hatched larvae emerge and again in early spring. Release and encourage parasitic Trichogramma wasps. Avoid planting spruce and fir trees in areas where the pest is prevalent.
- Squash bugs: These brown, green, or gray K-inch-long bugs and their nymphs attack the leaves of squash and pumpkins, causing the leaves to die. They become a problem when their population swells in late summer. Control by handpicking the bugs, growing vines on trellises, rotating crops, and cleaning up plant debris before winter.
- Squash vine borers: The adult lays an egg at the base of the stem in spring to early summer. After hatching, the larvae tunnels into the stem, causing the plant to wilt and eventually die. Control by covering plants with floating row covers early in the season. Remove the row covers at blossom time. Remove larvae from infested stems and cover the stem with soil, allowing it to root. Butternut squash resists this pest.
- Tarnished plant bugs: Among the most destructive pests of strawberries and other crops, plant bugs pierce the tissues of vegetable, flower, and fruit plants, and suck the sap. Their feeding damages the plants, causing swelling, dead spots, bud drop, and distorted growth. The brownish, flattened oval bugs, shown in Figure 8-16, move quickly when disturbed and spread plant diseases. Control by covering crops with floating row covers and encouraging or releasing predatory insects. Knock insects off plants into soapy water in cool morning or evening hours, when bugs are sluggish. Spray with neem or pyrethrins if necessary.
- Tent caterpillars: Adult moths lay eggs in midsummer in hard, dark-colored, shiny masses that encircle twigs of deciduous trees. Caterpillars emerge in the spring and form colonies in large tentlike webs on their host trees. Large infestations can defoliate an entire tree. Control by seeking out and destroying the egg masses in late summer, especially on apple, cherry, and aspen trees. In spring, break up the tents with a long pole, and before the caterpillars disperse, spray them with insecticidal soap. Knock caterpillars off severely infested branches with a broom and destroy. Encourage beneficial insects by planting carrot-family plants. Spray with Bt or spinosad in spring.
- Thrips: These tiny, slender-bodied flying insects damage all soft parts of ornamental and vegetable plants, including leaves, flowers, and roots. Infested flowers and young fruits look distorted. Leaves have silvery or white discolored patches on them, sometimes speckled with black. Use a magnifying lens to identify them. Encourage or release lacewings and other predatory beneficial insects. Spray with horticultural oil or hang blue sticky traps.
- Tomato hornworms: Once you see these caterpillars, you never forget them. The bright green larvae grow up to 4 inches long and as big around as your little finger, with white diagonal stripes along their sides and a black horn on their tail end. When disturbed, they may rear up and make a clicking sound. Handpick them and drop into soapy water, or spray small ones with Bt or spinosad. The large, gray-brown adult moths are 4 to 5 inches across and fly at night.
- Webworms: This group includes several moth species whose caterpillars spin webs or cocoons around themselves and their host leaf, which they devour. Fall webworms attack trees and shrubs in late summer; garden webworms prefer vegetables and strawberries; and turf webworms go after grass. Control by handpicking; breaking up nests; and spraying with insecticidal soap, Bt, or spinosad. Encourage beneficial insect predators.
- White grubs: Many beetle species lay eggs in the soil, which hatch into root-eating grubs. Common species of white grubs (see Figure 8-17) include June beetles, Japanese beetles, and rose chafers. Control with beneficial nematodes applied to the soil.
- Whiteflies: Resembling tiny, white moths, these insects (shown in Figure 8-18) congregate on the undersides of leaves, sucking plant sap and spreading plant diseases. Infested plants may release clouds of them when disturbed. Control whiteflies with insecticidal soap or light horticultural oil, or by trapping them with yellow sticky traps. Be sure to treat leaf undersides, where whiteflies and their larvae reside. Encourage parasitic wasps and predatory beetles.
- Wireworms: These 1-inch-long, copper-colored worms tunnel through plant roots and tubers, causing significant damage and opening wounds that encourage plant disease. Control the larvae by cultivating frequently and destroying the exposed insects. Chickens do a good cleanup job in my garden before planting time. You can also trap worms with pieces of cut potato placed in the soil. Check the potatoes for worms every few days and discard.
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