Controlling Garden Pest Populations

An ecosystem view of controlling garden pest populations while keeping beneficial insects healthy, including integrated pest management, pest control techniques and how to choose a pesticide.

| July/August 1982

  • 076-167-01
    Without deliberate manipulation by man, insects and other animal populations are naturally controlled by a variety of factors.

  • 076-167-01

William and Helga Olkowski are entomologists, founders of the Farallones Institute, authors of The City People's Book of Raising Food (Rodale, 1975), and co-directors of the Center for the Integration of Applied Science (a division of the John Muir Institute for Environmental Studies, Inc). Who, then, could be better qualified to offer us some timely advice. 

The article excerpted here first appeared in Horticulture magazine, June 1976. (Subscriptions: $18 per year from Horticulture, Subscription Department - TMEN, Boulder, Colorado.) Reprinted by permission of the authors. 


Without deliberate manipulation by man, insects and other animal populations are naturally controlled by a variety of factors. It is necessary to know something about these natural controls to understand why relying on synthetic chemical insecticides can have undesirable effects.

Weather is a commonly recognized factor. It may become too hot, too cold, too wet, or too dry for any particular pest population. Gardeners in every part of the country have their local examples of what such conditions as a freeze or a wet spring might mean in terms of problems later in the year. In California, for instance, the oak moth (Phryganidia californica ) overwinters as a small caterpillar upon the leaves of the live oak tree (Quercus agrifolia ). Normally, heavy rains and light freezes help to reduce its numbers during the winter months. But when the season is unusually dry and warm, many more caterpillars may survive to defoliate the trees when spring arrives.

Food supply is another factor affecting pest populations. On a farm, large monocultural stands of the same species of plant may allow a huge buildup of a pest. This is less likely to be a problem, however, in a small and more highly diversified home garden.

Habitat is also important as a limiting factor for animal populations. For example, when garden slugs are reproducing beneath boards that are placed directly on the ground as walkways in wet weather, by simply placing fine dry sawdust under the boards you can reduce the slug population while avoiding the problem of muddy footpaths at the same time.

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