Using low-risk pesticides prevents damage to nature

Studies have found that home gardeners are apt to apply more pesticides than farmers or landscapers and with the National Garden Association reporting that 85 million U.S. households engage in home gardening, the collective misuse of pesticides is an issue of growing concern.

Misuse of pesticides can have a number of unintended consequences, including damaging plants, intensifying pest problems and contributing to soil, air or water pollution. Certain pesticides persist in the environment for years, posing a threat to human health, wildlife and the overall health of the environment. In light of these repercussions, pesticides should never be used without careful consideration or outside of an integrated pest management program.

A systematic, preventive approach combining cultural, physical, biological and chemical controls is the only effective and sustainable way to manage pests. There are several nonchemical pest management strategies that can reduce or eliminate the need for pesticides in the home garden.

Cultural controls impede the colonization, spread and survival of pests and include crop rotation, intercropping, sanitation and use of pest-resistant varieties to ensure plants have the optimum conditions for health.

Physical controls are techniques that prevent pests from reaching host plants. They include removal, traps and barriers, such as floating row covers, sticky barriers or abrasive dusts.

Biological control methods involve the use and conservation of natural predators, parasitoids or pathogens that prey on pest species in your garden. (For more information on how to apply these strategies in your home garden, contact your local County Extension Office or Master Gardener Helpline.)

Chemical controls are a last resort. But first, you need to accurately identify the pest and understand its biology and life cycle. Most pesticides are only effective if applied at a certain stage in a pest’s life cycle. Many insecticides, for example, only kill pests in the larval stage and have no effect on the eggs or adult stages.

The final thing to consider is population size. Most plants can tolerate low to moderate levels of pest damage without noticeable effect. If a problem is severe enough to require pesticides, it’s important to select products that pose the least risks to human health and the environment.

There are a variety of low-risk pesticides suitable for the home gardener. A few of the least toxic will be discussed here.

Insecticidal Soaps

Insecticidal soaps are composed of fatty acids and potassium salts, which permeate the insect’s outer covering and disrupt the cellular membranes. Chemically similar to the soaps we use at home, insecticidal soaps are specifically designed to control pests and minimize plant injury. They are among the safest pesticides available because they don’t leave toxic residues and pose a minimal risk to non-target and beneficial organisms, with the exception of predatory mites.

Insecticidal soaps are generally effective against small, soft-bodied arthropods including aphids, thrips, soft scales, whiteflies, psyllids, mealybugs and spider mites.

Soap sprays easily damage some plants so it’s important to read the label before you spray.

Insecticidal Oils

Insecticidal or horticultural oils are highly refined plant- or petroleum-based oils that can be used to control certain pests and diseases, including aphids, whiteflies, mealybugs, scale insects, spider mites, psyllids, thrips, certain insect-vectored diseases, and some fungal pathogens such as powdery mildew, black spot and rust.

Oils work by disrupting insect respiration, cellular metabolism and feeding behaviors, smothering fungal organisms and interfering with the transmission of plant viruses. Similar to insecticidal soaps, oils are among the safest pesticides available because they leave no toxic residue and pose a minimal risk to non-target organisms.

Microbial Pesticides

Microbial pesticides are typically very host specific and only work against one target pest or closely related species. However, some microbial pesticides are broader in spectrum and can have negative impacts on non-target species.

Kim Perry is a University of Hawaii College of Tropical Agriculture and Human Resources extension agent and the UH Master Gardener coordinator on Kauai. Contact her via email at kperry2@hawaii.edu.