In an integrated pest management (IPM) system, biological controls might include predatory or parasitic insects, bacteria or fungi, and biopesticides. The huge biocontrol arsenal contains both tools for purchase and some that can be supported in the garden through cultural practices. Five examples of biological controls will barely scratch the surface of this rapidly growing area of IPM, but can provide insight into the world of biological controls and products that, with additional development, will become more readily available to the home gardener.
A diverse, healthy home garden contains numerous predatory insects. For many gardeners, the challenge is distinguishing predators from the harmful insects eating our plants. Close observation of the insects’ behavior and activities reveals that predatory insects less frequently occur in a group than plant feeding insects. Predators’ body parts are clues to their predatory nature — large eyes, large mandibles (jaws), raptorial front legs for grabbing prey. Predatory insects can be microscopic, so size is not an indicator. The minute pirate bug, found throughout North America, is about a millimeter long and feeds on thrips, whitefly larvae, and insect eggs. Minute pirate bug was an effective control agent in greenhouse crops when tested extensively in the 1990’s, but was unpopular because it frequently bit greenhouse workers. Today, numerous insect species are available for purchase by professionals: ladybird beetles and mantis egg sacs remain most common for home gardeners. Use of predators as control is effective with the correct combination of insect, temperature, and timing, often requiring research.
Parasites and parasitoids manage pests by laying eggs on or in another insect, which becomes a food source for the resulting offspring. A classic commercial example in greenhouse ornamentals is Encarsia formosa, a tiny wasp that parasitizes whitefly. Brown marmorated stinkbug, an invasive pest recently identified in multiple Oregon locations including Klamath Falls, is destructive to numerous fruits and vegetables. Recent Oregon State University work has identified a parasitic wasp that may serve as a control agent, known as the “Samurai wasp”: catalog.extension.oregonstate.edu/em9164. Parasitism takes place in the garden more frequently than most gardeners realize. There is even a fly that parasitizes monarch butterfly larvae! A home garden with diverse plant and flower types supports beneficial insects.
Biopesticides — insecticides
Biopesticides are derived from natural sources like bacteria, plant compounds, fungi, and the like. Bio-insecticides are those substances formulated to kill insects. Common examples of plant-derived bio-insecticides include products with neem, citrus, or eucalyptus oils. Common “BT” products are derived from a bacteria Bacillus thuringensis. There are different formulations and strains of BT for different target pests. Many biopesticide products are appropriate in an organic pesticide program. Biopesticides are currently the fastest-growing segment of pesticide development.
Biopesticides, herbicides and disease control
Bio- herbicides for weed control include products like mustardseed meal, clove and other herb- based oils. Some of these same oils and other plant-based products can be used to fight plant diseases. Research using these compounds is ongoing — results vary with the application method, the target problem, and the specific plant being treated. While biopesticides represent tremendous promise for less environmentally toxic solutions to insect and disease problems, anything that ends with “-icide” is a compound intended to kill something, whether it’s natural, Organic, botanically derived, or synthetic. Capsaicin products, derived from peppers, are irritating to all mammals. BT, used to control caterpillar pests and a component of many Organic pest control programs, is also lethal to desired caterpillars like monarch butterfly larvae.
Insect-killing (entomopathogenic) fungi
Most common in this category is the soil-dwelling fungus Beauveria bassiana, that, under some circumstances, controls grasshoppers and other insects. Current research seeks to determine whether this fungus can help control bedbugs, which have become largely resistant to formerly effective synthetic pesticides. Occasionally, the same fungus may be effective against both some insects and plant diseases! For instance, a fungus in the genus Lecanicillium is thought to be effective against both the green peach aphid and cucumber powdery mildew. These nuanced interactions don’t work the same for every combination of pests and plants. It takes considerable research to develop these insect-killing fungi into marketable products that can be used in home gardens — and the products may not be as easy to apply as conventional chemicals. While only a few fungi are used widely in agriculture, there is tremendous growth potential in the realm of insect and disease- killing fungi.
A classic example of biocontrol has a direct Klamath connection. The Klamath beetle, a non-native insect, was released in California and Oregon to eat the out of control Klamath Weed, a species of St. John’s wort. For more information on this early example of a successful biocontrol release in our corner of the word, see faculty.ucr.edu/~legneref/biotact/ch-66.htm.
Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Sanchez at 541-883-7131 or Nicole.firstname.lastname@example.org, or attend a “Garden Gab” session at Leap of Taste, fourth Friday of each month, 8:30 to 9:30 a.m.