Get Rid of Garden Pests

Get a handle on garden pests with these helpful tips.

By Gwen Kilcherr


Summer 2012

Aphids on Leaf

Integrated pest management is an important aspect of gardening and keeping plants healthy.

Photo courtesy www.RareSeeds.com

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Quite often when you see damage on the leaves of a vegetable plant, the plant is not necessarily in danger of dying, only being nibbled on by an occasional insect. Sometimes your plant will be nibbled away overnight by some hungry snail or slug, cut off at the base by a cutworm, or dug out of the ground by a squirrel. This can be frustrating when it happens, but remember that we share this earth with these creatures and your garden is also home to them. Most of the time, simple, time-tested control methods are the best solutions.

Integrated Pest Management

Integrated pest management (IPM) is the monitoring and identification of pests, and the subsequent control of those pests. After monitoring and gathering information about the pest, its life cycle, and environmental factors, you can decide whether the pest can be tolerated or whether it needs to be controlled.

IPM combines the most effective, long-term way to manage pests by using a combination of methods that work better together than separately. Approaches for managing pests are often grouped in the following categories:

• Biological control is the use of natural enemies—predators, parasites, pathogens, and competitors.
• Cultural controls use practices that reduce pest establishment, reproduction, dispersal, and survival.
• Mechanical and physical controls kill a pest directly or make the environment unsuitable for it.
• Chemical control is the use of pesticides, where the pesticides are selected and applied in a way that minimizes their possible harm to people and the environment. 

Insecticides are substances applied to control, prevent, or repel insects. Insecticides can be a part of IPM programs, however, some products can worsen the problem or harm people or wildlife. Products labeled “less toxic pesticides” cause few injuries to people and organisms other than the target pest. Even organic pesticides can be dangerous and can kill Honeybees and birds if overused.

The less-toxic insecticides listed below should be a first choice when choosing a pesticide. Pick any pest and you can usually find a natural control for it. Always check the product labels to be sure they are registered for that plant or pest situation.

Insecticides

Less-toxic insecticides include:

• Soaps (potassium salts of fatty acids). Insecticidal soaps control aphids, whiteflies, and mites and require complete coverage of pests and sometimes a repeat application.
• Insecticidal oils. Oils control aphids, lacebugs, mealybugs, psyllids, scale insects, spider mites, thrips, and whiteflies. Good coverage of plants is required. Don’t apply to water-stressed plants or when temperatures are above 90°F. Petroleum-based oil products include superior, supreme, narrow range, and horticultural oils. Plant-based oil products include jojoba, neem, and canola oils.
• Microbial insecticides. Microbials are derived from microorganisms that cause disease only in specific insects.
• Bacillus thuringiensis subspecies kurstaki (Bt) controls leaf-feeding caterpillars.
• Bacillus thuringiensis subspecies israelensis (Bti), sold as mosquito dunks, controls mosquitoes.
• Spinosad is a microbial-based insecticide that controls caterpillars, leafminers, and thrips, but it also can harm some beneficial insects.
• Insect-feeding nematodes. Nematodes species are microscopic worms that attack many underground insects.  Because they are living organisms rather than a pesticide, they are very perishable, so order through the mail to assure freshness.
• Botanical insecticides. Derived directly from plant materials, botanicals vary greatly in their chemical composition and toxicity but usually break down in the environment rapidly.
• Pyrethrins (pyrethrum) are used against a range of insects but toxic to fish and aquatic organisms.
• Azadirachtin, from the neem tree, has limited effectiveness against pests but low toxicity to nontargets. Don’t confuse with neem oil.
• Garlic, hot pepper, peppermint oil, and clove oil are sold as insect repellents that protect plants.
• Non-toxic and homemade remedies. Homemade remedies are inexpensive and, best of all, you know what’s in them. Many homemade sprays have been used with good results to control insects. They usually involve noxious (but non-toxic) ingredients such as garlic, cayenne, stinging nettles or horsetail which are diluted in water and blended to be sprayed on the plants.

Avoid these more-toxic pesticides:

• Pyrethroids such as permethrin, cyfluthrin, cypermethrin, and bifenthrin move into waterways and kill aquatic organisms.
• Organophosphates such as malathion, disulfoton, and acephate are toxic to natural enemies.
• Carbaryl harms bees, natural enemies, and earthworms.
• Imidacloprid is a systemic insecticide that can be very toxic to bees and parasitic wasps, especially when applied to flowering plants.
• Metaldehyde, a common snail bait, is toxic to dogs and wildlife. Use iron phosphate baits instead.

Cultural Controls

The easiest and first way to prevent insect damage in your garden is to discourage the pests from coming in. A healthy garden is your best defense. Here’s how to ensure that:

• Pull out weak plants. They may already be infected, and if not, they will attract problems.
• Build a healthy soil. Composting methods, adding organic matter, mulching and top-dressing your soil with compost or natural fertilizer is the best way to develop strong, vigorous plants.
• Seaweed mulch or spray contains trace elements such as iron, zinc, barium, calcium, sulfur and magnesium, which promote healthy growth in plants. Seaweed fertilizer in mulch or spray form will enhance growth and give plants the strength to fight off disease. Seaweed mulch also repels slugs.
• Minimize insect habitat. Clear the garden of debris and weeds which are breeding places for insects.
• Interplant and rotate crops. Insect pests are often plant specific. When plantings are mixed, pests are less likely to spread throughout a crop. Rotating crops each year is a common practice to avoid re-infestation of pests which have over-wintered in the garden.
• Keep foliage dry. Water early so the foliage will be dry for most of the day. Wet foliage encourages insect and fungal damage to your plants.
• Disinfect. If you've been working with infested plants, clean your tools before moving onto other area in the garden. This will reduce the number of invading insects.
• Hand-picking. For small infestations, hand-picking is an effective and easy way to remove insects. Fill a jar with water and a few teaspoons of liquid soap and take it into your garden. When you see a caterpillar or insect, pick it from the plant and drop it into the jar. Squish small insects like aphids against a leaf with your fingers.
• Companion planting. Some plants have natural properties that repel insects. Plant these companions next to plants that are susceptible to insect attack. For example, plant onions near cole plants to repel cabbage loopers, and marigolds next to tomatoes and peppers to repel root-knot nematodes in the soil.

Mechanical Controls

Mechanical controls include traps and barriers such as:

• Yellow flypaper. Old-fashioned fly-paper is very effective in the garden for aphids and whiteflies. In fact, any board or heavy paper painted yellow and coated with a sticky substance will do the job.
• Pheremones. These biological mating scents attract insects to a trap which is coated with a sticky substance. Pheremone traps are effective, but remember they are “attracting” the insects, so be sure to position them on the outskirts of the garden perimeter or you'll attract them straight to your garden!
• Floating row covers. These consist of lightweight opaque fabric that’s draped over the garden bed. Sunlight and water can penetrate, keeping insects and birds out. The material is so light that the growing plants lift it up as they grow. Anchor down the edges with rocks or boards or the wind will blow it off. Row-cover fabric comes in rolls so you can make a continuous cover no matter how long the garden bed is. Row covers are very effective for protecting seedlings. When placed over vegetables such as beets, broccoli, cabbage, spinach and swiss chard, it makes an effective barrier against flying insects looking for these plants on which to lay their eggs.
• Cloche. The cloche acts like a miniature greenhouse for seedbeds and young plants, and acts as a barrier against pests. Unlike the floating row cover, the cloche has to be opened on hot days and for watering. It helps seedlings and young plants get well established, developing their natural resistance against pests and disease.
• Barrier paper. Milk cartons are a simple, effective way to protect plants from cabbage moths larvae. They kill young sprouts of the Brassica family (broccoli, cabbage, brussel sprouts, kale or cauliflower) by nibbling at the base. Cut the cardboard into 2" squares and slit one side into the center; make another small slit crossways. Open the slit and slide the square so the seedling stem is in the center. This prevents the cabbage moth from laying eggs at the base of the sprouts. As the plant grows, it will push the slit open wider.
• Spray protection. Use diatomaceous earth as dust or in a water-spray for effective control of hundreds of species of insects. It works by scratching their exoskeletons and dehydrating them. Insecticidal soaps are made up of fatty acids that break down the cell structure of the insects’ exoskeletons and cause dehydration. Oil or wax sprays coat the insects’ bodies and smother them. Some oils and waxes contain other ingredients such as capsaicin (hot pepper oil), which is toxic to insects. These remedies are broad-spectrum and are toxic to beneficial as well as harmful insects.

Biological Control

Most garden insect pests have natural enemies. Biological controls include beneficial insects and may be parasitic insects or bacteria that infect specific species, or they may be carnivorous insects that will attack and eat the pests. 

Garden “mini-insectary.” Set aside a small garden plot of flowering plants designed to attract and harbor beneficial insects. These good insects prey on many common garden insect pests, and offer the gardener a safer, natural alternative to pesticides.

• Brachonids, chalcids and Ichneumon wasps: These small beneficial insects attack leaf-eating caterpillars. You can attract them to your garden by planting carrots, celery, parsley, caraway and Queen Anne's lace. Leave some to flower because it's the flower that attracts the insects.
• Ladybugs: These common insects consume aphids, mites, scales, and whiteflies.  Attract them to your garden by planting flowers of the Compositae family such as tansy or yarrow. Ladybugs can be purchased at your nursery or from catalogs and released directly into the garden.
• Lacewings: Lacewings love aphids and a variety of other insects. They’re also attracted to “composite” flowers, such as asters, black-eyed Susan, goldenrod, and yarrow. Lacewings can also be purchased and released directly into your garden.
• Hover-flies: These also enjoy aphids. The larvae of hover-flies eat other insect pests as well. Like the lacewings, they are attracted to composite flowers.
• Praying mantis: These large insects have an appetite for most garden pests. Praying mantis eggs are set out in the garden where they hatch and quickly grow to adult size. The eggs are available at nurseries and through catalogs.
• Nematodes: Nematodes are effective against cutworms that eat the sprouts before they can grow into seedlings. Nematodes are also effective against beetles and root weevil larvae. Nematode eggs are microscopic and come in a small sponge containing over a million eggs. They are mixed with water and applied to the soil, where they hatch and get to work. If they get on any foliage, wash them off to the ground. They are available in some nurseries and through mail-order catalogs.

Common Pests

The tomato hornworm is definitely the scariest pest in the garden, growing up to 5 inches long, but actually quite beautiful. They are heavy feeders of the tomato and can eat quite a lot of leaves. Female moths lay eggs under the leaves of the tomato plant and once they hatch and start feeding, they grow quickly. They eventually make their way into the ground, pupate, and become adult moths.

Roto-tilling in spring helps prevent worms, and rotating the tomatoes each year can help. The best way to get rid of them if you have a problem, is to look for them at dusk when they are most active. They can be very hard to find because of their green coloring. They leave black droppings behind and that can help you spot them. Picking them off does the trick, so just keep checking for new damage through the season.

An organic substance called Bacillus thuringiensis, or BT, is a powder you can spray on the underside of the leaves to kill the eggs. It washes off quickly in rain and must be applied once a week.

Cabbage worm larvae are green and very hairy, with an almost velvet-like appearance. Older larvae are up to 1 inch long and often have one faint yellow orange stripe down their backs and broken stripes along the sides. Adults are white with one to four black spots on the wings. They can cause a lot of damage to leafy green plants by eating holes in the leaves. Cover the plants with a row cover or spray BT to prevent these caterpillars from doing serious damage.

The cabbage moth is the pretty white butterfly fluttering around in the garden that we don’t think could possibly be causing any damage. This butterfly can lay eggs on a plant, and within a few days they are hatched and eating their weight in leaves every day. The eggs of the cabbage moth will be found underneath the leaves. Cover the plants up with row cover or spray BT to prevent these caterpillars from doing serious damage.

Parsley worms (black swallowtail caterpillar) are really beautiful, being white and green, with black bands and yellow or orange spots. Many people grow parsley for their ability to attract them to the garden because they turn into the beautiful black swallowtail butterfly. However, if you are growing parsley to eat the parsley, make sure you watch for signs of the butterfly and either cover the plants up with row cover or spray BT to prevent these caterpillars from doing serious damage. Picking off caterpillars usually keeps them under control, just keep checking for new damage throughout the season.

For slugs, snails, and earwigs (and other soft-bodied garden pests), sprinkle diatomaceous earth around plants and around edges of garden beds. The diatoms particles are very small and sharp, and are only harmful to the small exoskeletons of insects, slugs and snails. Insects cannot become immune to its action, as it’s a mechanical control, not a chemical one. They are leaf and stem eaters and love to eat basil and leafy garden vegetables. They eat all night long and hide in dark, cool, damp places all day long.

The most commonly used prevention is the slug and snail baits that are sold in garden centers. They do work if you follow the directions on the box and reapply when it rains. The best way to prevent snails and slugs is to create barriers that they cannot cross over to get to your plants. Any type of copper strip can be used to make a wall that electrically shocks their body; wood ashes, crushed egg shells, or diatomaceous earth will cut into their soft flesh. Eliminate as many of the snails as you can find. Go out into the garden at night with a flashlight to collect them, place boards propped up slightly where they’ll hide under during the day, then go out in the afternoon and remove them from the underside of the board and destroy them. Follow their slime trails to track them down. Beer traps work by drowning slugs but not many snails as they are not really beer drinkers.

Encourage natural enemies such as birds, frogs, salamanders, and toads; chickens and ducks are also efficient snail hunters.

The Mexican bean beetle (adults are yellow-brown, 1/4 inch long, with 16 black spots) and the Japanese beetle (adults are a brilliant metallic green, generally oval in outline, 3/8 inch long and 1/4 inch wide) both attack bean plants as well many other plants, eating away at the leaves until they look like lace. Watch for them June through August when the adults are actively feeding and hand-pick them. Phermone traps also work well. Check under the leaves for egg sacks and remove them. If the damage is visible, lay a cloth under the plants and shake the stems until the beetles fall off the plant. Collect them on the cloth and dispose of them. The best pre-treatment for Japanese beetles is Milky Spore, a bacterial powder that kills only Japanese beetle grubs (larvae), while they are feeding underground in the fall.

Aphids and whiteflies are more of a nuisance than damaging, but if left alone, can create a colony very quickly which then can cause a lot of damage. Whiteflies are small flying insects that when disturbed, will flutter around the plant. Aphids are small, non-flying insects which, depending upon what they are eating, will determine their color. They suck the sweet juices out of the soft, tender, new leaves.

Aphids and whiteflies will usually attack plants that are under stress of some kind.

Mix two tablespoons of hot pepper sauce or cayenne pepper with a few drops of liquid soap into a quart of water. Let stand overnight, then stir and pour into a spray bottle and apply as above. Shake container frequently during application.

Or, you could mix one tablespoon canola oil and a few drops of liquid soap into a quart of water. Shake well and pour into a spray bottle. Spray the entire plant. The oil will smother the insects.

Ready-to-use and concentrated insecticidal soaps work well and can be purchased at nurseries. You may need a couple of treatments but it will get rid of them eventually.

There is also an organic spray, called Neem, that is even better than the soap spray. It is made from Neem oil and is combined with Pyrethrum from the Chrysanthemum plant, which works on many types of insects as a deterrent and a killing spray.

Spinosad is a natural insecticide. The active ingredients are complex organic compounds made by soil microbes. It is a broad-spectrum pesticide but is only active if ingested or contacted while in liquid form, so it has little residual effect on most beneficial species.

The squash vine borer is a real pest of squash, gourds and pumpkins. The caterpillars reach a length of 1 inch and have a brown head and a cream-colored body. The adult squash vine borer is a stout dark gray moth with hairy red hind legs, opaque front wings, and clear hind wings with dark veins.

Symptoms appear in mid-summer when the vine or entire plant wilts suddenly. Infested vines usually die beyond the point of attack. Sawdust-like frass near the base of the plant is the best evidence of squash vine borer activity. Look for yellow brown excrement pushed out through holes in the side of the stem at the point of wilting. If the stem is split open, one to several borers are usually present and can be easily pulled out by hand. The stems should be immediately covered with earth. Burying a few nodes along each vine will encourage rooting at these nodes. This will lessen the impact if squash vine borers girdle the base of the vine.

Natural pest control methods such as keeping your garden clean and weeded, using mulches and good compost in the soil, and applying organically made pesticides when necessary.

Sanitation is also important. After harvesting, the vines should be removed from the garden and disposed of to prevent the remaining borers from completing their larval development.

Healthy, happy, plants grown organically in good, nutritious soil, have a natural immunity to pests and diseases and in the long run can protect our environment from overuse of pesticides.

It is not necessary to kill every insect in the garden, as many pesticides do, because many beneficial insects which eat other pests can be killed and this can create a worse problem. There are also many living creatures in the soil which help to break it down and provide nutritious soil for your plants which can also be killed such as earthworms and bacteria.