Barriers & Exclusion Techniques for Arthropods
This is the second article in a two-part series on trapping and excluding arthropod pests. The first article appeared in the Summer 2013 issue of Utah Pests News, and focused on common methods to attract and trap arthropods (insects, spiders, mites, and relatives) for monitoring and management. This article will cover common techniques to keep arthropods away from plants and out of buildings.
Barriers can be physical or chemical in nature. Use of arthropod barriers can be a good fit for home gardens, buildings, and small-scale agricultural settings. The time and labor required to install and maintain barriers can limit their use for large-scale pest management.
Physical Barriers - Exclusion from Plants
Placing barriers over or around plants can be highly effective in reducing injury from some arthropod pests. In many cases, barriers are best suited for use during the seedling, bloom, or fruiting stages when plants are most susceptible to pest damage. Using barriers during targeted, limited time periods will reduce the amount of labor to maintain the barriers.
- Sticky barriers can be placed as a band around a trunk, limb, or stem to exclude climbing insects and mites. Example pests include earwigs, spider mites, ants, codling moth, elm leaf beetle, and others. Sticky adhesives, such as Tangletrap, can be purchased or made by mixing one part petroleum jelly and one part household detergent. For tree trunks, apply the adhesive on a surface, such as duct tape, to protect the bark. Remove accumulated insects and debris from bands and add fresh adhesive added as needed.
- Shields (6-inch diameter) made from tar paper or foam rubber can be placed on the soil around seedlings in the cabbage family, bean, pea, corn, beets, and tomato to prevent egg-laying by the cabbage and seedcorn maggot flies. Shields can also serve as hiding places for predatory ground beetles that will eat maggot eggs and larvae, as well as other pest insects in the garden.
- A ¼ inch thick layer of diatomaceous earth or crushed egg shells placed around vegetable and ornamental plants (4-6 inch diameter circle) can deter crawling pests, such as caterpillars, earwigs, snails, and slugs. These “mine fields” of sharp shards tear holes in the outer protective body layer, causing them to desiccate.
- Cutworm collars can reduce losses to vegetable seedlings from caterpillars in the cutworm family. Collars can be constructed from metal, plastic, foil, cardboard, or other sturdy and flexible materials. They should be at least 4 inches tall, and placed securely into the soil to about 1 inch depth. The top edge of the collar can be bent outwards to enhance its effectiveness in preventing cutworms from crawling over the top.
- Bagging fruit to exclude codling moth, peach twig borer, yellow jackets, European paper wasp, and other pests can be highly effective. Fruit clusters must be thinned to a single fruit and bags applied before the target insect is active. Nylon mesh fruit bags are available from horticultural suppliers or can be homemade.
- Covers or cages placed over plants can prevent feeding damage and egg-laying by many insect pests, including leafminers on leafy greens, caterpillars and cabbage maggots on cole crops, flea beetles on mustard crops, aphids, beet leafhoppers that vector curly top virus, and others. Floating row covers are made from a strong, permeable fabric, and should be secured over plants before pests are present. Row covers are permeable to air, light, and water, and allow continued plant growth. Cages can be large enough to cover an entire crop row, such as a ventilated plastic or row cover suspended on a frame, or small enough for a single plant, such as a cone constructed from window screen. If the crop requires pollination, covers and cages must be designed for removal, or vented to allow bees access to plants during bloom.
- Copper bands or strips can be placed around tree trunks, raised beds, and other structures to exclude snails and slugs. The copper ions carry an electric charge that repels the gastropods.
Physical Barriers - Exclusion from Buildings
Many insects and spiders become nuisance pests when they enter buildings to seek shelter. Prevent their entry by caulking cracks and crevices in foundations, walls, and especially around basement doors and windows; install weather-stripping around doors; screen attic vents; and repair window and door screens and ensure screen frames fit tightly. Remove thick vegetation, debris, and heavy mulches next to foundations, especially around basement doors and window wells. Keep firewood stacks and other debris where arthropods may hide at least 20 feet away from inhabited buildings. Don’t store firewood indoors.
Techniques such as these and similar ones can be highly effective as physical barriers in preventing entry of pests into the home or workplace.
In most cases, use physical barriers and other non-chemical techniques before resorting to insecticides. For prevention of structural damage to a building, such as from termites, chemical controls are often needed in addition to physical barriers and cultural practices to reduce the attractiveness of the site to the pest. To conserve beneficial insects, only apply insecticides when deemed necessary.
Insecticides can be applied as a chemical barrier around buildings or plant beds. Populations of migrating pests, such as grasshoppers, can be reduced by placing at least a 6 ft wide barrier of granular insecticide formulated as a bait. Granular bait formulations of spinosad, a bacterial insecticide, can be applied as barriers around fruit trees and berry bushes to exclude earwigs. Insecticides can be applied to the soil around the foundations of buildings to exclude insects and spiders.
Use of barriers are one component of an integrated pest management approach. The goal of IPM is to achieve balanced and sustainable pest management while preserving the environment and human health. For small-scale pest management situations, barriers can provide a low cost and simple way to reduce pest problems.
-Diane Alston, Entomologist
Cornell University Horticulture Diagnostic Laboratory. 1992. Insect traps and barriers (3 pp.). Cornell University Cooperative Extension of Suffolk County, Riverhead, NY.
Flint, M. L. 1998. Pests of the Garden and Small Farm, 2nd ed. (276 pp.). Statewide Integrated Pest Management Project, University of California, Division of Agriculture and Natural Resources Publication No. 3332, Berkeley, CA.