Beneficial Garden Insects Help Reduce Creek Pollution

September 11, 2004

By Dale Norrington

Gardening practices, like many other human activities, can significantly influence water quality in local creeks. Pesticides and fertilizers, for example, may wash from lawn and garden surfaces and via curb and gutter systems enter creeks, often without treatment or filtration. Erosion control, use of porous paving materials, and other on-site water retention strategies help reduce pollution of runoff water bound for local creeks. Proper use and appropriate disposal of pesticides, fertilizers, paints, lacquers, and petroleum products help reduce pollution. UC recommended Integrated Pest Management practices can also contribute to improved creek water quality.

A component of Integrated Pest Management is maintenance of habitat within gardens to support populations of beneficial insects. Beneficials help control pests including aphids, scale, whitefly, mites, and others, which can decrease need for insecticides. Lady beetles, lacewings, various species of wasps, dragon flies, damsel flies and damsel bugs, syrphids, pirate bugs, and bigeyed bugs are among the many beneficials welcome in the garden. Minimization of pesticide use is in and of itself important to maintenance of habitat suitable for beneficial populations. Ant control, dust control, incorporation into gardens of structurally diverse selections of insectary plants, and water are also important.

Insectary plants supply beneficials with nectar and pollen, shelter, and habitat for the various stages of insect reproduction. Insectary plants may also serve as desirable alternate pest hosts. Ideally, a garden would include such insectary resources throughout the year. Pollen and / or nectar are typically available when a plant is in bloom.

UC Publication 3386 notes the following insectary plants which can provide pollen and nectar during the various seasons in California gardens:

· Winter Salix spp., Ceanothus spp., redbud, coyote brush, buckwheat, and mule fat;

· Spring yarrow, coffeeberry, hollyleaf cherry, toyon, and soapbark tree;

· Summer buckwheat, elderberry, creeping boobyalla, bottle tree, and narrow leaf milkweed; and

· Fall coyote brush and buckwheat.

Alfalfa is a relatively easy to grow legume, potentially an excellent pollen and nectar source, and a versatile ground cover / shrub. Plant it in rows or borders, as a cover crop, in and around fruit tree basins, or interspersed in a patchwork fashion through the garden. Lilac hued Buddleia alternifolia (Butterfly bush), and vigorous B. Davidii (Summer lilac), available in a variety of colors, are possibilities for spring bloom. Asclepias tuberosa (Butterfly weed), a milkweed relative, can provide bright, orange-hued, mid-summer bloom. Hardy, drought tolerant Lantana spp. of various color and form can bloom continuously over multiple seasons. Rudbeckia spp. (Cone-flower, Black-eyed Susan, or Gloriosa daisy), available as annuals, biennials, and perennials, are relatively easy to grow, tolerant of most garden conditions, and may bloom from summer through fall. Coreopsis spp. may tolerate varying conditions and show yellow from spring through fall.

Welcome beneficials with suitable garden habitat, and let the good bugs help keep the creek safe and clean.

University of California Cooperative Extension Master Gardener Volunteers can provide additional gardening information upon request. Call the San Luis Obispo office at 781-5939 on Mondays and Thursdays from 1 to 5 PM, the Arroyo Grande office at 473-7190 on Wednesdays from 9 AM to 1 PM, or the Paso Robles office at 237-3100 on Wednesdays from 9 AM to Noon.  The San Luis Obispo Master Gardener website is at http://groups.ucanr.org/slomg/. Questions can be e-mailed to mgsanluisobispo@ucdavis.edu.