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So you want to control pests naturally....

Zapping garden pests used to be as simple as that... one blast with a chemical spray killed them, and they vanished, at least for the time being. After years of searching for the right chemicals--killing good bugs along with bad--more gardeners today are using products that control garden pests effectively and safely without adversely affecting the garden's health.

Many such products are appearing in nurseries now. Some are insecticides derived from plants, and some are modern versions of pesticides our great-grandparents used, such as soaps and oils. One method is devious: pitting bug against bug.

Do these new products and techniques really work? The answer is a qualified yes. Few of them provide the quick fix that some gardeners expect, but all can keep pests' numbers down.

Effective pest control requires close and frequent observation of your plants. If you choose the right plants and keep them healthy and groomed, they can outgrow many pests. A healthy garden has lots of living things-- including a few aphids or whiteflies for beneficial insects to feed on.

On these pages, we look at gardening techniques, beneficial organisms, and nontoxic and low-toxicity chemicals that are practical controls for home garden use.

Before you begin to control a pest, you must identify it. Books, knowledgeable nursery personnel, or county extension agents can help. Then you can choose the best defense.

1. Be a good gardener

The easiest way to control pests is to create an environment that either discourages them or reduces plants' susceptibility to them. Choose ornamental and edible plants that are well adapted to your area.

Adjust planting time. If planting early would avoid a sure-thing pest, do so. Plant corn early to avoid corn ear-worms; plant gladiolus early to avoid thrips. Spider mites are most troublesome when weather turns hot; plant beans early to avoid them. As soon as plants become infested, remove them. Keep records of planting dates and temperatures so you can make adjustments from season to season.

Choose pest-resistant varieties. Certain plants are more susceptible to insect pests than others. Eucalyptus long-horn borer beetles won't damage some species, such as E. cladocalyx. Nematode-resistant tomatoes have the letter N after their names.

Check with your local cooperative extension office for information about edible and ornamental plants best suited to your area.

Solarize the soil. Before planting, you can use the sun to heat the soil-- an effective way to reduce or eliminate soil-inhabiting pests. Just before the hottest time of year (usually mid-July), cultivate soil and remove weeds. Water soil, then lay 1-1/2 to 2-mil clear plastic over it; anchor edges with soil. Leave in place for four to six weeks.

Set out traps. Nurseries and catalogs sell several kinds, for specific pests (snails and slugs, wasps and whiteflies). To trap earwigs, put short sections of garden hose, rolls of corrugated cardboard, or rolled-up newspaper on the ground.

Use barriers or row covers. Often the easiest way to eliminate pest damage is to place a physical barrier between the pest and your plant. To thwart cutworms and snails, put bottomless cans around vulnerable seedlings. Floating row covers of spun fiber or plastic applied before seedlings emerge make an impenetrable barrier to pests, especially tough-to-control ones like aphids, cucumber beetles, flea beetles, root maggots, and whiteflies.

Copper bands around trunks of shrubs and trees block snails. Sticky barriers stop or slow ants, snails, and beetles from climbing. They're available at nurseries as sprays, in squeeze tubes, or in tubs (vegetable gum-based products are less harmful to plants than petroleum-based ones). Be prepared to renew them frequently, and don't let pets or children play near them (they're messy).

Wash plants. Frequent washing of plants with water or insecticidal soap eliminates some aphids, mealybugs, and spider mites before they can multiply (mites prefer dusty, dirty plants and low humidity). Do this early in the day so leaves will dry before nightfall.

2. Get the help of beneficial insects

Among the most common beneficial organisms are predatory or parasitic insects. Predators, such as lady beetles, attack and consume pests directly. Parasites, usually tiny wasps, use pests as food sources for their offspring. Adult parasites lay their eggs in, on, or near a pest insect; the offspring grow in the host pest, eventually killing it.

These "good" insects work by reducing pest numbers until they are no longer sufficient to damage the plant, though they don't eliminate pests entirely. For example, over a two-year period beginning in October 1989, entomologists distributed more than 130,000 Encarsia partenopea wasps, tiny parasites of the ash whitefly, in parts of California. By September 1991, ash whiteflies had become so few in those areas that they were difficult to find. On the other hand, the Type B sweet-potato whitefly became an agricultural crisis late last summer in California's Imperial Valley after repeated sprayings with very toxic pesticides.

But buying living insects is not as simple as buying a jar of spray. They are alive, so must be moved quickly to your garden. Set delivery dates to minimize storage time. Release beneficials during the cooler evening time.

Whether you already have beneficial insects living in your garden or want to release some, you need to protect them from ants, which maintain colonies of pests such as aphids and scale in order to harvest their honey-dew. To eliminate all routes ants might use, prune away tree branches that touch the ground, walls, or other trees. Then apply a sticky barrier around trunks of trees and shrubs.

Keep in mind that ants are survivors, and almost anything you do to kill them will only disrupt them for a time. Baits such as half-and-half mixtures of sugar with epsom salts or boric acid help, as do traps containing nontoxic or low-toxicity chemicals such as boric acid or hydramethylnon (sold as Combat). Ants are very susceptible to insecticidal soap sprays, which also wash away their trails.

One novel approach is to feed them. Put a bowl of sugar or fallen fruit near their nest; well-fed ants are much easier to live with than ones you're trying to kill.

Not all ants protect insect pests. Red ants kill some pests, but they don't bother beneficials, and they suppress Argentine ants.

To encourage natural and introduced beneficials to stay in your garden, use nectar-like yeast-sugar solutions; several are commercially available. Nectar-producing flowers, especially ice plants, rosemary, and thyme, and many in the daisy, carrot, and legume families such as alfalfa and clover attract and sustain populations of beneficial insects.

Many birds, frogs, lizards, spiders, and insects (including wasps, damsel bugs, assassin bugs, big-eyed bugs, minute pirate bugs, soldier bugs, and predatory ground beetles) feed on insect pests. Encourage the greatest possible diversity of beneficials by planting many kinds of flowering plants, and by not using toxic chemicals. In a healthy environment, beneficials increase naturally.

Decollate snail (Ruminia decollata). A snail that feeds on brown garden snails. Use one decollate snail per square yard. If hungry, these snails will climb trees and eat tender growth. They're legal only in Southern California. Cost: about $25 for 100.

Delphastus beetle (D. nigrus). A lady beetle that feeds voraciously on the sweet-potato whitefly. Cost: $50 for 100 adults.

Fly parasites. Tiny wasps (many species). These lay eggs in the pupae of several species of flies, including houseflies. Very effective and most useful in ranch or farm situations. Release them early in the season; also use supplemental controls such as traps. Cost: about $15 for 5,000 wasps, enough for an area containing 5 large animals (horses or cows), or 7 to 10 smaller ones (dogs) for a month.

Green lacewig (Chrysoperla carnea). Occurs naturally in most gardens. Larvae feed on many soft-bodied insects--aphids, thrips, pear psylla--and on insect eggs and mites. Cost: about $15 for 5,000 eggs, enough for about 1,000 square feet.

Lady beetle (Hippodamia convergens). Occurs naturally in most gardens. Adults and larvae feed on aphids, mealy-bugs, small worms, spider mites, and similar soft-bodied insects. Releasing them in your garden is often not effective because they fly. Also, they migrate annually. Release in evening because daylight encourages flight. Cost: $10 for 500 beetles, enough for 500 square feet.

Mealybug destroyer (Cryptolaemus montrouzieri). A species of lady beetle. This Australian native has an orange head and tail and black body. It feeds on all above-ground mealybugs, as well as aphids and immature scale. Does not survive cold winters. Cost: $15 for 100 beetles, enough for 500 square feet.

Parasitic nematodes (Heterorhabditis, Steinernema, and others). These microscopic worms seek out and eat their way into more than 250 kinds of soil-dwelling pests such as grubs, weevils, sod webworms, and carpenter worms. Cost: $15 for enough to treat 225 square feet.

Predatory mites (Amblyseius, Metaseiulus, and Phytoseiulus). Usually transparent to salmon in color; move quickly to eat pest mites. Cost: about $30 for 500, enough for 250 square feet.

Scale parasites. Tiny California red scale parasite wasps (Aphytis melinus) attack and kill red scale and other kinds of hard scale. Black scale parasite (Metaphycus helvolus) attacks black scale and other soft scale insects. Release in late summer or fall. Make supplemental releases as necessary. Cost: $5 to $15 per 1,000.

Syrphid flies (many species). These bee-colored flies are common garden visitors that must feed on pollen to reproduce. Their larvae feed on aphids and other insects. They're not commercially available, but you can buy kairomones that attract them.

Trichogramma wasps. They are tiny--four or five can sit on the head of a pin. They lay eggs on the eggs of more than 200 species of moths and butterflies, including cabbage loopers, codling moths, corn earworms, and tomato hornworms. Cost: about $15 for 50,000 parasites, enough for about 1,000 square feet.

Whitefly parasite (Encarsia formosa). Tiny wasp attacks immature stages of greenhouse whitefly and is most effective in greenhouses. Release them early in the season when whitefly numbers are low. For best results, release at two-week intervals (four releases total) when temperatures are above 75[degrees]. Cost: about $20 for 500 parasites, enough for about 500 square feet. To control ash whitefly, a related species that is not commercially available has been released in California.

3. Use less-toxic chemicals, sprays, dusts

Sulfur, soaps, and oils are some of the oldest and most useful controls. Other non-toxic controls include minerals and organic by-products. According to the California Organic Food Act and the California Certified Organic Farmers, the following (except for Azadirachtin) are acceptable for use on or around organically grown produce.

Azadirachtin. From the African neem tree (Azadirachta indica), this liquid spray is nontoxic to mammals; it stops feeding of many insects and prevents normal growth of immature insects. Not yet registered for use in California or Arizona.

Bacillus thuringiensis (BT). This microbial insecticide is generally toxic only to leaf-feeding caterpillars; the spray has no effect on adult butterflies and moths. Use it sparingly and only on plants that host pests caterpillars if you wish to encourage butterflies to reproduce in your garden. Mixing it in alkaline water (pH 8 or above) reduces effectiveness. Apply it thoroughly when caterpillars are small; reapply in 3 to 14 days.

The strain for most caterpillars is B.t. berliner. Other strains available include B.t. israeliensis for mosquitoes, B.t. kurstaki for corn borers, and B.t. 'San Diego' for Colorado potato beetles and elm leaf beetles. Apply with feeding stimulants (available by mail from sources listed on page 120) so caterpillars will consume more BT.

Horticultural oils. Highly refined petroleum oils smother insects and sometimes their eggs. Use during the dormant season on leafless trees and shrubs to reduce the number of overwintering insects. Use in summer to control aphids, pear psylla, scale insects, mites, and eggs of some insects. Oils can burn sensitive leaves; test the spray on small area of plant before complete spraying.

You can make your own mixture to use on growing plants with a formula devised by the U.S. Department of Agriculture. Combine 1 cup of cooking oil with 1 tablespoon of liquid dishwashing detergent. Add 1-1/2 teaspoons of the mixture to 1 cup of water to control aphids, beet armyworms, spider mites, and whiteflies. The mixture tends to burn leaves of cauliflower, red cabbage, and squash.

Insecticidal dusts. These fine, powdered materials cling to, scratch, and destroy the waxy exteriors of some pests. Diatomaceous earth, boric acid, and silica aerogels are among the most useful, though they can be hazardous if inhaled. Use natural-grade, not pool-grade, diatomaceous earth to discourage ants, slugs, and snails.

Boric acid, usually a dust or powder, is also available as a spray or paste, and in baited traps. Silica aerogels absorb the moisture from an insect's body, killing the insect. In the garden, apply as a dust for ants, fleas, and ticks.

Insecticidal soaps. These mixtures of specific fatty acids are of low toxicity to humans and many beneficial organisms but toxic to most small insects and mites. They act fast, leaving no residue, and are safe to use on edibles. They work best in warm soft water. Apply in early morning or late in the day when spray will dry slowly, prolonging the effect. Combine with citrus oil or mint tea (in place of water) to enhance effectiveness.

Lime sulfur. A liquid spray of calcium polysulfides that controls mites and pear psylla, as well as some plant diseases such as peach leaf curl. Widely used for fruit trees.

Semiochemicals (pheromones and kairomones). Insects use these synthetic chemicals to communicate. Two kinds are commercially available: pheromones, which affect mating behaviour, and kairomones, which affect feeding behaviour. Both are used to attract insects--sometimes to trap or confuse an insect pest, and other times to lure beneficials into the garden. They are very target-specific and exist for many common pests. For instance, one pheromone can lure codling moths into a trap. Kairomones attract many beneficial insects, such as syrphid flies and lacewings, to the garden.

Sulfur. Applied as fine dust, will kill mites; it also controls plant diseases such as brown rot, mildew, and scab. Can burn plants if used when temperature is over 90[degrees].

4. Use natural insecticides

These insecticides are all derived from plants. Because they are natural and break down quickly into nontoxic compounds, they create few environmental problems. But they may be toxic to people or animals. All but sabadilla are safe to use around bees.

Pyrethrum. Extracted from dried, powered flowers of Chrysanthemum cinerariaefolium that are grown in Kenya and Tanzania. This insecticide is effective against many insects but is noted for rapid knockdown of flying ones. It breaks down within a few hours after exposure to sunlight. (Pyrethroids, synthetic versions of natural pyrethrum, are more toxic and persist much longer in the environment.)

Rotenone. This spray or dust, extracted from roots of tropical legumes such as Derris, Lonchocarpus, and Tephrosia, controls chewing insects, including beetles, weevils, loopers, thrips, and flies. It's a slow-acting stomach poison, fairly toxic to mammals (especially hogs) and very toxic to fish. It's quick to degrade.

Ryania. Stomach poison derived from powdered stem of the tropical shrub Ryania speciosa. Controls codling moth, citrus thrips, corn earworm, and asparagus beetle, but is gentle to beneficial insects.

Sabadilla. Made by grinding seeds of sabadilla lily (Schoenocaulon officinale). Acts as stomach and contact poison against caterpillars, leafhoppers, thrips, and squash bugs. Low toxicity to people but highly toxic to bees. Registered in California only for citrus thrips.

Sources for hard-to-find pest controls

If you can't find some products listed, the following mail-order suppliers have good selections of low-toxicity pest control products.

Arbico, Box 4247 CRB, Tucson 85738; (800) 827-2847, in Canada (800) 665-2494. Beneficial insects, least-toxic controls.

Biofac, Inc., Box 87, Mathis, Texas 78368; (512) 547-3259. Insectary; raises and sells beneficial insects.

Bio-Insect Control, 710 S. Columbia, Plainview, Texas 79072; (806) 293-5861. Beneficials, natural insecticides.

Harmony Farm Supply, Box 460, Graton, Calif. 95444; (707) 823-9125. Beneficials, natural insecticides.

Hydro-Gardens, Box 9707, Colorado Springs, Colo. 80932; (800) 634-6362 or, in Denver, (719) 495-2266. Beneficial insects and other supplies for greenhouse growers and small farms.

IFM, 333 Ohme Gardens Rd., Wenatchee, Wash. 98801; (509) 622-3179 or, in the United States only, (800) 332-3179. Beneficial insects, natural insecticides.

Necessary Trading Company, One Nature's Way, New Castle, Va. 24127; (703) 864-5103 or, in the United States only, (800) 447-5354. Beneficials, natural insecticides, other garden products.

Peaceful Valley Farm Supply, Box 2209, Grass Valley, Calif. 95945; (916) 272-4769 ($2 catalog cost refunded with first order). Wide variety of products.

Rincon-Vitova Insectaries, Inc., Box 96, Oakview, Calif. 93022; (805) 643-5407. Raises and sells beneficial insects.

Ringer, 9959 Valley View Rd., Eden Prairie, Minn. 55344; (800) 654-1047. Wide variety of products; the only source for Neem (Azadirachtin).

Sterling International, Inc., Box 220, Liberty Lake, Wash. 99019; (800) 666-6766. Traps, pheromones, beneficial wasps.

For more information on using beneficial insects with other controls, see The IPM Practitioner ($25 per year), Common Sense Pest Control Quarterly ($30 per year), and other practical booklets from the nonprofit Bio-Integral Resource Center, Box 7414, Berkeley 94707; (510) 524-2567. Catalog $1. A 715-page book, Common Sense Pest Control, by William Olkowski, Sheila Daar, and Helga Olkowski (The Taunton Press, Newtown, Conn., 1991; $39.95), summerizes everthing you may want to know about the least-toxic controls.

Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, by Mary Louise Flint (ANR Publications, University of California, 1990; $25), describes proven techniques for managing pests without using toxics. Call (510) 642-2431, or write to Publications, Division of Agriculture and Natural Resources, University of California, 6701 San Pablo Ave., Oakland 94608. Also available from the same source is a 17-by 24-inch poster, Natural Enemies Are Your Allies ($5), which shows color photos of 20 of the most common beneficial insects.
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Title Annotation:includes related articles
Author:MacCaskey, Michael
Date:Apr 1, 1992
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