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THE ORGANIC LANDSCAPE: Trees and shrubs, a commen sense approach

by Marcel Beauchamp



When I began my tenure as foreman of the Dominion Arboretum of the Central Experimental Farm, I inherited a somewhat dated and, in my view, unnecessary system of insect and disease control which essentially consisted of spraying with chemical pesticides at regular intervals to ensure that pests didn’t get out of control. Through my readings, I became familiar with a concept known as Integrated Pest Management (IPM), a system used successfully in orchards and forestry for quite some time. IPM recognizes that a plant or group of plants, whether in a natural or landscaped setting, is a component of a functioning ecosystem where the mere presence of a pest does not constitute a problem. The unrealistic aim of eradicating pests is abandoned in favor of controlling pest populations to acceptable levels using control measures that are least disruptive to the ecosystem. Chemical controls are a last resort with IPM in a conventional setting. In an organic setting, organic pesticides such as rotenone, Bt (Bacillus thuringiensis) and insecticidal soap are used as a last resort. I began using this system in the Arboretum with the hopes of nurturing back to health an ecosystem that had been abused for many years by repeated use of pesticides.;

Naturally, I duplicated these efforts on my own property, being particularly determined not to use any chemicals at home. Through vigilant monitoring in both environments, I was able to observe many natural forces at work. I came to rely on a number of these: small mammals such as shrews, deer mice and bats; and parasitic and predatory insects such as ladybugs and soldier beetles. Many of these may go largely unnoticed because of their small size and nocturnal habits. Birds also became an important part of my natural controls. By paying particular attention to their needs for shelter and food and by avoiding pesticides, I was able to encourage and augment the number and variety of these excellent predators. ;

However, birds aren’t always capable of controlling insects to the extent that gardeners would want. When natural controls don’t do the job to our liking, we need to turn to something that will. Personally, I have found that for the majority of insect problems I may encounter on my trees and shrubs, I can rely on a combination of Bt and insecticidal soap. I combine the two ingredients in a small sprayer and use it with excellent results on pests like tent caterpillars, aphids, and sawfly larvae of pine, birch, and mountain ash. The Bt takes care of all caterpillars of moths (Lepidoptera) while the soap kills aphids and sawfly larvae. I have found that the soap also has an insecticidal effect on the caterpillars, but the two together are more effective than either product used by itself.;

In addition to these natural and imposed controls, I have found that attention to certain cultural techniques can have a very positive effect on a plant’s health, which in turn can enhance its natural resistance to insects and diseases. What causes a breakdown in plants’ immunity is stress. When plants are attacked by insects, they produce their own toxic substances which ward off the attackers. Weakened or stressed plants have difficulty producing these toxins or cannot produce them in sufficient quantities.;

Gardeners can help reduce or prevent stress on plants by following some simple cultural practices. Select a healthy plant to begin with and you can avoid many future headaches. As the first few years of a tree or shrub’s life are very important in establishing its health in the years ahead, choose a variety that will thrive and grow where you expect it to spend the rest of its life. Matching the plant’s basic needs (soil type, moisture and light) with site conditions greatly increases chance of success. Never buy or dig up plants that are spindly, sickly looking, or already infested with insects or diseases.;

Use up-to-date planting procedures to minimize transplant shock and maximize prompt establishment of the roots into their new home. An adequately large planting hole is very important as overcrowding the roots in too small a hole can, over time, choke a tree and lead to a slow decline and even death. Use mulches over the root zone of newly planted trees and shrubs for the first three to five years to encourage quick establishment of a strong root system. Keep the zone weed-free and water it frequently and deeply the first year or two to avoid drought stress. Be careful not to injure the trunks of young trees with lawn maintenance equipment, as that creates serious stress and may present opportunities for pathogens to infect the tree. Over the years, as trees and shrubs grow and mature, good pruning techniques are essential to minimize stress and reduce the likelihood of infectious diseases getting a foothold in the wound that is created when pruning off a branch.;

These techniques form part of a valuable integrated approach that includes a variety of preventive measures aimed at not only optimizing a plant’s health so it remains naturally resistant to pest infections, but also at encouraging a host of natural controls, reducing the necessity of imposing artificial controls. These techniques have been used successfully in the Arboretum and on my own property, and can be very easily adapted to smaller urban backyards, which are really only part of a larger neighborhood ecosystem. Consistency in the application of these principles will ensure success.;

For more detailed information see COG’s Chemical-Free Care of Trees and Shrubs – A Guide, RS 12/90.;



Marcel Beauchamp worked as foreman of the Dominion Arboretum from 1981 to 1988. There he introduced IPM to reduce dependency on chemicals. He teaches adult evening courses in organic gardening techniques for the Ottawa Board of Education and gardens organically on his five-acre property near Morewood, Ontario.




Copyright 1995. Marcel Beauchamp.

Reprinted with permission. All rights reserved.

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