Barriers That Keep Pests Away From Your Garden (Part 2)

Tree Bands: Barriers around tree trunks can be used to prevent pests from crawling up the trunk, so they're an effective control for insects that can't fly. Tree bands can be coated with sticky materials to make them into traps. Tree bands are excellent barriers for older gypsy moth larvae, because they migrate daily from the treetop down the trunk to hide in leaf litter during the day, then climb back up at night to feed. Barriers are also useful on apple trees to intercept codling moth larvae looking for a place to spin cocoons, and on citrus to stop snails, ants, and beetles.

How to make: Estimate or measure the circumference of the tree trunks you plan to barricade. Cut 8 to 12-inch-wide strips of cotton cloth or burlap of the appropriate length for each tree. Be sure strips are long enough to overlap at the ends when wrapped around the tree.

As soon as trees leaf out in spring, tie bands of cotton cloth or burlap to tree trunks with a string around the middle of the cloth. Pull the top section of cloth down over the string so the cloth makes a dead end for pests trying to climb the trunk. If used for gypsy moth larvae, check daily in late afternoon and destroy the larvae. For codling moth larvae, removing the pests once weekly is sufficient.

You can also use corrugated paper or cardboard to form tree bands by wrapping several layers of it around the trunk, with the exposed ridges facing the tree. Tie with string. The larvae will seek shelter in the spaces between the paper and the bark. Remove the bands weekly and destroy the larvae. Continue this practice throughout the summer. You can reuse the bands until they wear out from handling and exposure to weather.

You can buy silicone-coated, flexible tape that is too slippery for ants and beetles to cross. Simply wrap this tape around the trunk to form an impassable barrier. On rough-barked trees, put a band of sticky compound like Tangle-Trap or Bug Gum along the inside edges of the top and bottom of the tape to prevent insects from crawling up or down through crannies between the tape and bark. Put an extra band of the adhesive along the outside top to stop insects that do manage to cross the slippery tape.

Snail-repellent tapes are also available to wrap around trunks. These have a sticky backing and are coated with cayenne pepper and salt to repel snails.

Copper Barriers: Copper is very toxic to slugs and snails, and copper strips wrapped around tree trunks or stems of shrubs make a highly effective slug and snail repellent. Some scientific studies indicate that copper is effective because slugs and snails actually get an electric shock when they touch it. It's theorized that the slug's slimy coating interacts chemically with the copper, creating an electric current. Using copper strips as a permanent edging for borders or beds is an effective but expensive way to keep slugs and snails off flowers and vegetables.

How to use: Estimate or measure the circumference of the stem or trunk of the plant. Use a copper strip that is longer than the circumference, so you can enlarge the strip as the plant gets bigger. Punch holes in the ends of the strips. Fasten the copper strip securely around the trunk or stem by feeding a piece of wire through the holes and twisting it tight. Remove suckers, water sprouts, and nearby weeds that might provide alternate routes for the snails
and slugs to reach your plants.

To make a copper barrier around a flower or vegetable bed, bury a 3 to 4-inch-wide copper strip around the edge of the bed or border, with 2 to 3 inches of the copper exposed. Then bend the top 1/2 inch of the strip outward at a right angle to form a lip. Check the enclosed area and get rid of any slugs or snails that are already inside. Once they are removed, the bed or border should stay slug-free.

To protect plants on greenhouse benches, staple copper strips directly to the sides of wooden benches and around wooden legs. Or staple strips to wooden blocks mounted between bench supports and the top. Make sure the benches don't touch the greenhouse wall or glazing, because slugs can climb them to reach your benches as well. Protect plants grown at floor level with strips of copper as you would a bed or border.

Ant Barriers: Ants feed on aphid secretions. In fact, ants will actually carry aphids onto plants to set up a food source, then tend them and protect them from predators. Ant barriers on legs of greenhouse tables prevent ants from climbing up to seedlings.

How to make: Cut a hole that corresponds in size and shape to a cross-section of each table leg through the center of an aluminum pie plate . Slide an inverted pie plate up each table leg. Fold each pie plate downward to form a cup and coat the inside of the cupped plate with a sticky compound like Tanglefoot. Be sure the crack between the pie plate and the table leg is sealed with caulking or Tanglefoot. Renew the sticky compounds when necessary; if the greenhouse isn't too dusty, the sticky surfaces may last as long as one year. You can leave these traps in place permanently to guard against ants.

Dehydrating Dusts: Insects have complex internal systems that minimize water loss when they breathe and a waxy or oily cuticle that prevents water loss through body surfaces. Any dust or powder that scratches this waxy coating destroys the insect's water balance and can kill the insect. These materials can be used as barriers because insects will try to avoid them. Slugs and snails also prefer to avoid dust and powder barriers but will cross them if they get hungry enough.

Dusts work well against cabbage root flies and, if renewed frequently, will reduce carrot rust flies. When painted on tree trunks, dehydrating dusts repel ants and may help deter adult forms of borers from laying eggs on the bark. Dehydrating barriers also have some effect on slugs.

To make a dehydrating dust paint, mix 1/4 pound diatomaceous earth with 1 teaspoon of pure soap, like Ivory liquid, and enough water to make a thick slurry. Applying this paint to the lower trunk gives double protection; it shields the bark from the sun as well as discourages pests. Spread a circle of dry wood ashes, diatomaceous earth, talc, or lime around any plants being attacked. Cover the area out to the dripline, or at least within a 6-inch radius of the stem. To deter cabbage root flies from laying eggs around the stems of cabbage family plants, heap a cone of diatomaceous earth or other dust around the stems at the soil line. Dust barriers are most effective when they're dry, so re-apply after it rains or after you water the garden.