California Native Plant Society

Managing Pests

Problems with plants can be caused either by vertebrates, such as rodents or deer, invertebrates like nematodes, insects or mites, or fungi and disease. The Integrated Pest Management approach advocated here emphasizes mechanical control, such as physical barriers and careful cultivation, and an understanding of the life cycles of plants and their predators.

The first step in pest management is selecting the right plant for the right area. Choosing the right plant for your site will translate into healthier plants and reduced pest problems. Water needs, soil type, exposure, and function and form all enter into the selection of an appropriate plant or landscape suite. Front yards are often landscaped differently than backyards. Homeowners and gardeners have different criteria and needs for landscaping. You can access a helpful guide for analyzing your site conditions and selecting the appropriate plants for your site by clicking here.

One very important concept in pest management is threshold or action level. When does the pest population and subsequent damage reach a level that requires action? This threshold level can be very different for front versus backyards. If gardeners and landscapers can relax their pest threshold for a time, natural predators will often build up populations that will control the problem. Plantings in public areas or schools may need to meet different criteria (a more stringent threshold level) for public safety.

The University of California’s Integrated Pest Management (UC IPM) website is a wonderful guide to the least toxic, IPM treatments for home and garden pests that have crossed the threshold and require some type of management.

The UC IPM site contains environmentally and scientifically sound recommendations that meet most management needs including: less radical methods, such as hosing insects off the plant; and soft pesticides such as detergent, oil sprays or Bt. These methods are considered to be environmentally friendly and less detrimental to beneficial insects and other natural predators. Pesticide alternatives are also listed to provide management in difficult situations.

Compared to introduced plants, California native plants are likely to be less troubled by native “pest” organisms because they have co-evolved. Damage from pests is usually cosmetic and temporary. Such “damage” can even be welcomed - such as with caterpillars like the large Ceanothus silk moth, or with Oak galls and oak moths which have evolved with oak trees in California for millions of years. It is common practice to plant for butterflies, why not plant for caterpillars and beetles? In the backyard, most pests of native plants can easily be tolerated especially when predator and prey insects and vertebrates are in balance, creating a huge potential for education and enjoyment in the garden. Human intervention can destroy the balance. Change your treatment threshold and enjoy the show. If a variety of seeds, fruit and shelter are available in the yard to attract birds, they can be our allies, taking insects, especially in spring, to feed their young. If the plants are carefully matched to soil type, sun exposure and irrigation, they will be less liable to be impacted by insect pests, fungus and disease.

Information Contributed by:
Allison Shilling, Sacramento Valley Chapter
Robert Case, East Bay Chapter


Other References

CNPS Phytophthora Policy:
Native Plant Group Supports Clean Nursery Practices (Press Release) (PDF)
CNPS Phytophthora Resources

O’Brien et al. 2006: Care and Maintenance of Southern California Native Plant Gardens (in English and Spanish). Most of this is applicable to California in general. Brief descriptions of pests alphabetically, as well as a very useful table of native plants giving their most frequent problems. detailed descriptions of pests, their habits and controls, though the emphasis is on vegetables and non-native ornamentals. With links to color photos.

Weed Management in Lawns and Landscapes
Flint M.L. Published 1998 Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, Second EditionPublication 3332 -
$35.00 - 286 pages - ISBN 1-879906-40-6 These companion books have very good introductions on pest management; for both invertebrates and diseases there are excellent color photographs of the damage caused to the plants.

Dreistadt et al. 2004: Pests of Landscape Trees and Shrubs, Second Edition
Publication 3359 - Published 2004$42.00 - 501 pages - ISBN 1-879906-61-9


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