   Least-Toxic Pest Control for Indoor Plants - May 10, 2006 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Indoor plants can have a range of pests including aphids, mealybugs, mites, thrips, fungus gnats, and whiteflies. Some of these can also exude honeydew which can also attract ants. Since indoor plants are in close proximity to humans and pets, many people are concerned about using synthetic pesticides. In recent years, products with lower human/mammalian toxicity have been developed to reduce pesticide exposure risk to people and non-target organisms while also minimizing negative effects on the environment. These products are often called “least-toxic” pest controls and can be used in combination to control plant pests. To be effective in any pest control program, you must first correctly identify the pest species which you are targeting. This can often be done by close inspection. Aphids can be green, black, yellow, or red and are usually found on the growing plant tips. Scales can either be soft-bodied or armored. Soft scales produce sticky honeydew. Mealybugs are a mobile form of soft scale with a white, waxy coating that also exude honeydew. Mites are microscopic and therefore more difficult to detect. They leave behind small holes and fine webbing. The tops of damaged leave often appear stippled with silvery or yellowish dots. Thrips are also very small and can fly when mature. They can be detected by gently tapping the affected part of the plant against a white piece of paper and inspecting with a magnifying glass. White flies are tiny, sap-sucking insects. The larvae (nymphs) look somewhat like scale. The adults are white and can often be seen flying around the plant. Sticky Traps In situations where house plants are grouped together, blue or yellow sticky traps are useful for attracting and trapping flying adult fungus gnats, whiteflies, thrips, and others. These are colored cards that attract insects. Upon landing, an insect become stuck to the cards due to an adhesive coating. Blue sticky traps attract thrips and yellow sticky traps attract whiteflies. Sticky traps are often used to monitor for pests in greenhouses. Soaps Soaps are salts of fatty acids. Fatty acids are found naturally in plants and animals and when reacted with metal salts, they become soap. Formulations of liquid soaps are sold commercially as insecticides. Soaps disrupt insect cell membranes causing their cells to rupture and collapse. Soaps are virtually nontoxic to the user unless ingested in large amounts. Soft bodied insects such as mites, aphids, scale crawlers, whiteflies, and thrips. Bees, beetles, wasps, flies, and grasshoppers are relatively unaffected. A 1 to 2% solution of household soap or detergent can be used, but are not as effective as soaps specifically formulated for insecticides. A 1% solution is about 3 tablespoons per gallon. Homemade soap solutions, especially those containing citrus extracts, are also more likely to negatively affect plant growth than commercially available insecticidal soap products. Horticultural Oils Horticultural oils are highly refined petroleum oils that contain added surfactants (an additive that allows them to be mixed with water and applied as a solution). In general, oils kill all stages of insects by smothering them. Oil also kills eggs by penetrating the shells and interfering with metabolic processes and/or interrupting respiration. They can cause skin and eye irritation, so protective clothing, gloves, and goggles should be worn when applying. Before using, plants should be well watered and the spray should be tested on a small portion of the plant to see if the plant is sensitive to the oil. Beneficial Nematodes Beneficial nematodes are not a pesticide, but microscopic round worms in the genus Steinernema and Heterorhabditis. They live in the soil and feed on many plant pests. Beneficial nematodes feed on the larval stages of fungus gnats. Juvenile nematodes carry Xenorhabdus sp. bacteria in their pharynx and intestine. Once the bacteria are introduced into the insect host, death of the host usually occurs in 24 to 48 hours. As the nematodes grow, they feed on the insect tissue that has been broken down by the bacteria. After maturation, the nematodes exit the insect carcass and live free in the soil. There is no evidence that parasitic nematodes or their symbiotic bacteria can develop in vertebrate hosts. Always follow label directions when using pesticides. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |