While many different chemicals are effective against pests, every bonsai enthusiast should keep the following items on hand. These chemicals, when combined with a good routine of pest prevention, should handle most of your problems:

What to keep on hand

1. Liquid Dish Soap. Spraying a very mild solution of warm soapy water on your trees is an excellent way to prevent a wide variety of diseases and discourage pests. Most books recommend trying several baths of soapy water before trying more powerful chemicals.

2. Chewing Tobacco. The nicotine in tobacco is a toxic and powerful chemical. It works as a "systemic" pesticide, creating an environment that many common sap-sucking pests find very distasteful. Make a mild tea by soaking tobacco in boiling water. Let it cool and water the trees with it. If used periodically, this treatment also prevents soil insects.

3. Safer's Insecticidal Soap. This mild pesticide is a version of liquid dish soap. It is one of the milder and safer insecticides if you have children and/or pets. Spray the trees weekly to discourage infestation.

4. Malathion. Malathion, a thiophosphate, is a broad-spectrum pesticide developed by American Cyanamid. It kills insects on direct contact. The chemical vaporizes easily and should be used early in the morning when the air is cool. Malathion works on almost all common pests except mites.

5. Kelthane. Kelthane, whose chemical name is dicofol, is commonly referred to as a "miticide". Like Malathion, it works by direct contact. It is the first choice for controlling the red spider mite.

Sprays, dips, drenches, and systemics

Pesticides come in four forms. Sprays are applied topically and usually kill pests on direct contact. Dips are also topical, but are more concentrated. To use a dip, fill a bucket with the appropriate mixture, then dip your tree upside down into the bucket keeping the soil dry. Drenches are watered into the soil; they control soil pests.

Systemics are watered into the soil, but are absorbed by the root system and respirated out through the leaves. Systemics make the entire tree poisonous, so use caution if children and pets may snack on your trees.

LD50 Rating

All pesticides have toxicity ratings. The LD50 rating indicates the lethal dosage ("LD") necessary to kill 50 per cent ("50") of the insects in the test environment. The test determines the amount of a chemical required to reach 50 per cent effectiveness. The lower the rating, the more toxic the chemical. The most toxic of the commonly used chemicals is Nicotine sulfate with an LD50 rating range of 50 to 60. Vapona, also highly toxic, has an LD50 rating of between 56 and 80. Malathion varies from 885 to 2800; Kelthane is around 800. Some chemicals with low LD50 ratings may require permits for their use. Always use caution when dealing with chemicals that have very low LD50 ratings.

Common pests

Ants: Ants generally don't harm most trees and may help control aphids and other insects. To avoid ants, keep potted trees off the ground. Ants love the cambium layer of wisteria and can quickly destroy this tree from the inside out. Treat the soil with Dursban, Sevin, or spray with Malathion.

Aphids: Many varieties of the aphid include the greenfly, blackfly, and white plant lice. They resemble tiny grasshoppers and cluster on stems, shoots, and fruit. Aphids feed on the sap of young growth, leaving a sticky residue behind. Use a systemic insecticide or spray with Malathion.

Caterpillars: Caterpillars come in a multitude of varieties. They destroy trees by eating the leaves. Use a systemic insecticide or spray with Malathion.

Cuckoo Spit: This unusual tiny bug lays its eggs inside a protective barrier of saliva, which resembles a white froth. The larvae feed on the sap flowing through a plant's leaves. Spray with Malathion.

Earthworms: Worms are more of a nuisance than a real threat. They may attract birds that dig in your soil. Submerge your tree's soil in lukewarm water for 15 to 30 minutes, and the worms will come to the surface.

Earwigs: These large, reddish brown bugs use pinchers on their tail and at the end of each leg to poke holes in the leaves. Spray with Malathion.

Leaf Miners: These are the larvae of flies and moths that hatch from eggs laid on the underside of leaves. The larvae bore into the leaves and feed on the soft, interior tissues, leaving telltale tracks. Use a systemic pesticide.

Leaf Rollers: These worms create a shelter out of a leaf by rolling it up around themselves. They then eat the leaf. Spray with Malathion.

Mealybugs: These tiny, white creatures resemble and are related to scale insects. They suck sap and leave a sticky honeydew, which may attract ants. They lay their eggs in white, cottony clusters of fluff. Wash with warm soapy water every 10 days. Use Malathion if that doesn't work.

Mites: Also called cyclamen mites, these tiny bugs drink the sap of trees. They are small, white or pale green, and hard to see without a magnifying glass. An infested tree's leaves will curl, wrinkle, streak, or turn grayish in color. Treat with Kelthane every week for three weeks.

Nematodes: Microscopic worms come from using nonsterile soils, such as leaf compost and get into the root system of a tree. The roots develop lumpy gauls where the organisms are growing, which often leads to other root infections. The worms stunt a tree's growth and eventually kill the tree. Nematodes cause a big problem in the Southeast. Some books recommend discarding the tree if it is not an expensive one. Otherwise, clean the roots thoroughly, cut out all visible infestation, and treat with a nematocide such as VC-13. Wash your hands thoroughly before handling your other trees; these worms spread easily.

Oribatid Mites: These tiny bugs feed on the algae that grows on the underside of the bark on deciduous trees, but are not dangerous to the tree itself. They look like tiny maroon or black pinheads. They also feed on aphids and can be used to control aphid infestation.

Red Spider Mites: These pesky little bugs are bright red and extremely tiny. They can destroy a juniper before you even know they are there. Red spider mites thrive in dry, hot conditions. Treat with Kelthane; apply once a week for three weeks since they lay eggs every seven days.

Roaches: Roaches feed on the leaves of trees. They breed in warm, moist soil, such as pine bark mulch. Treat the ground with Dursban or spray with Malathion.

Scale: This bug resembles a turtle shell. It lives on the underside of leaves and along the stems of soft-plant tissue where it leaves a sticky residue. Trees in the ficus family are especially prone to scale. Spray with a diluted rubbing alcohol.

Slugs & Snails: These slimy creatures feed on the leaves of deciduous trees by sanding the surfaces and digesting the particles. Affected leaves look like lace, with a telltale trail of slime. Use commercial baits containing metaldehyde, or try a saucer of beer to drown the pests.

Sow Bugs: These pests, often called roly-polies, are tiny crustaceans rather than insects. They feast on roots and stems and tender shoots. Spray with Malathion.

Springtails: This insect has a spring in its tail and is one-sixteenth of an inch long. It lives in wet soil, chewing on leaves and other fallen plant material. The presence of springtails indicates that you are over-watering. Reduce watering and treat with Malathion.

Thrips: These insects are very tiny, almost microscopic bugs with brush-like wings. They rasp the surface of leaves and especially blossoms, then suck the juices. You may notice dark excrement specks before you actually see the thrips. Spray with Malathion.

Whitefly: These moth-like insects are juice-sucking pests and spread quickly from tree to tree. Treat with a combination of Malathion spray and a systemic insecticide to kill the mature insects, the eggs and larvae.

Woolly Aphid: This common member of the aphid family resembles a tiny cottonball. When smashed, the bug shows its bright red insides. Use a systemic insecticide or spray with Malathion.