by Dave DeGroot - The Greater New Orleans Bonsai Society

This article was submitted by Earl Eckmann who obtained it from an old BCI magazine. It should be noted that several of the insecticides mentioned in this article are no longer available due to their potential for irreversible effects on humans and the environment. Some have been replaced by other types of chemicals (i.e. both Lindane and Chlordane have been replaced with Pyrethoid materials. Nicotine sulfate has been replaced with Rotenone) Check with your local extension service or garden center which can help you with a replacement. In the article, I have placed N/A after those materials I know have been withdrawn from the market. The basic ideas presented here are still valid - USE EXTREME CAUTION WHEN USING INSECTICIDES and FOLLOW DIRECTIONS EXACTLY- ED.

With a long, cold and relatively insect-free winter behind us, it is now time to return to the unpleasant task of fighting off the many insect pests that have already arrived. For the various types of insects with which we must deal, we have available three general types of insecticides -- oil emulsion, contact and systemic.

OIL EMULSION, or "dormant sprays" as they are often called, are actually a type of contact spray, but the method of killing is different than that of the poisonous contact sprays. Emulsifiable oil contains an agent which causes the oil to break up into such tiny droplets that they remain in suspension in water rather than floating to the surface. The oil and water therefore appear to "mix." The emulsion, when applied to a plant, deposits an extremely thin oil film which remains as a residue after the water evaporates. The film does not interfere with plant respiration, but clogs the pores in the exoskeletons of any insects on the plant, thereby smothering them. Oil sprays are non-toxic, so they are effective only against insects which are on the plant when it is sprayed. Its primary targets are scale insects, mealy bugs, red spider and white fly. It is also effective against the eggs and larvae of certain insects which may be deposited on a plant. Oil sprays should be used on deciduous trees when they are in their dormant state as soft, new foliage ma y b e harmed. Evergreens, both broad-leaf and conifers, may be sprayed, except for certain species of juniper. Some maple may also be sensitive, so check label information before using.

Oil sprays have the advantage of being non-harmful to people, pets or the environment, are fairly thorough and have, long-lasting effectiveness. Their primary drawbacks are a limited season for application, in the case of deciduous materials, and the fact that they can cause plant damage at temperatures lower than 45° or higher than 85°F. Oil sprays are most often used as "preventive medicine" during a period when both plants and insects are relatively inactive.

CONTACT POISON SPRAYS make up the bulk of available insecticides. These sprays, usually organic compounds, attack the nervous systems of insects. Contact sprays are most effective when sprayed directly onto the offending insects, although most have at least a short residual action, so that insects can be killed even if they arrive after the plant has been sprayed. The most popular contact spray used is MALATHION, because it is effective against soft insects such as aphids, yet it is not too dangerous to use and it breaks down quickly into non-harmful residues. Because Malathion is not highly toxic, some insects seem to shrug it off -- ants, slugs, and some types of caterpillars in particular often escape harm. In cases where Malathion fails, liquid Sevin may be used. Sevin is normally used in the vegetable garden because it does not alter the taste of foods as some sprays do, but it can be used effectively on Bonsai as well, against a variety of chewing and sucking type insects. Nicotine sulfate is an old but effective contact spray.

For insects that feed inside plant tissue, such as borers and leaf miners, something other than a simple contact poison is required. SYSTEMIC INSECTICIDES are those which are absorbed by the plant tissue either through the root system or the foliage. Systemics may be used to kill existing pests or as a preventive measure, because once absorbed by the plant, they do not break down as do contact poisons, but maintain a residual effectiveness that may last from several days to about 2 weeks. There are various brands of granular systemics on the market, but they all contain as their active ingredient O,O-Diethyl S- [ 2 - (ethy l thio) ethyl]phosphorodiothiate. The granular form is placed at the base of the plant and watered in, as is a chemical fertilizer. Take care with these – start with one quarter to one-half the recommended dosage and try it on some unimportant bit of potted material before using it on your good Bonsai. The advantage of this type of insecticide is that it can be used cleanly and safely – no mixing or spraying; the wind won’t blow it away or the rain wash it off.

There are available on the market today several good types of COMBINATION INSECTICIDES -- liquids which are effective contact sprays and also are absorbed by the foliage (to varying degrees) so that they are effective against internal pests as well. Most are related to the granular systemics in that they have some form of Diethyl phosphordiothiate as an active ingredient. The most common of these sprays is DIAZINON(N/A). It is relatively safe to use, and attacks leaf miners in soft-leaved plants. Its drawbacks are that it is not always as effective as one may wish, and I have heard that it is potentially harmful to Malphighia. Since I don't want to test this theory on my own Bonsai, I use Lindane(N/A) with good results. Lindane is also effective against borers which primarily attack oaks and members of the prunus genus, but may also get into other trees, especially where wounds or scars exist. If a borer problem is not extensive, try placing a little nicotine sulfate( N/A) directly into the hole(s) and then cover with paper or tape. This can be used instead of a systemic.

When all else fails, you can turn to Spectracide or Isotox (To Be Reformulated). These are two very effective insecticides that kill pests both on and in your plants but use them sparingly as they are extremely toxic and while safe for your plants, will kill just about anything that moves. Use with care!

Insecticides should always be mixed exactly according to label directions. Don't spray on a windy day or when rain threatens, as the insecticide will only be wasted and become a pollutant. When spraying, wear a mask if you have one. Use insecticides only when necessary as they kill off beneficial creatures such as lizards, toads and ladybugs as well as harmful insects. Often scale or mealy-bug-can be picked or scraped off of plants, especially the highly visible "oyster shell scale".

Caterpillars can be killed individually, as can slugs and snails, with a tweezers or stick. Ants often indicate the presence of aphids. Kill the aphids and usually the ants will go away. If, however, ants take up residence in the container, they can damage a plant by removing soil from around roots. If this is a problem try driving them out by soaking the container for several hours in a pan of water. Drain and dunk the pot several times, or water thoroughly from above before dunking, to make sure air pockets are not trapped in the soil to serve as a refuge for the ants. If this fails Chlordane(N/A) can be used, but it is very poisonous, and its toxic residues remain in the environment. Don't use it unless necessary.

Even if you have many trees, avoid using a hose attachment for spraying. Such a device wastes a lot of insecticide and usually does not do a good job anyway. Use a hand-held mister to thoroughly wet the undersides as well as the top of the foliage, and spray only the plants that need it. Don't douse a plant with insecticide if you can't identify the problem. The plant could have a type of fungus disease against which an insecticide would be useless. Take the plant, or a part of it, to the area horticultural service for a free diagnosis, and use the recommended treatment.

For all the good that insecticides can do, healthy trees and a cleangrowing area are still your best defense against insect pests.