Cankerworms, commonly known as inch worms, are small insects that feed on the leaves of many common trees in North America. They can cause significant damage to maples, beeches, oaks, cherries, elms, apples, lindens, ashes and hickories. The cankerworm can also spin silk threads to lower themselves onto nearby foliage, therefore defoliation on large trees can lead to damage on shrubs and flowers on the ground below them. You can employ a few methods of eliminating cankerworms from your yard and preventing extensive damage to your trees and shrubs.
Place adhesive bands around the tree trunks. You can purchase these at garden supply stores. Female cankerworms do not have wings and must climb up the tree in order to lay eggs. Adhesive bands will trap the females so they cannot make their way to the leaves of the tree. Male cankerworms may be attracted to the trapped females and will also be trapped as they inch toward them.
Spray chemical treatments on the foliage of the trees affected by cankerworms. Pyrethoid insecticides have proven effective in killing cankerworms and will linger on the leaves to kill insects days after an application. Spray the insecticide while the larvae are still small, but after all the eggs have hatched. For the best results, spray the insecticide in the fall and again in the late winter.
Kill cankerworms with naturally occurring bacteria. Sprays containing the spinosad bacteria will effectively kill cankerworms while still being safer for the environment than traditional pesticides. This makes spinosad a good choice if you are spraying trees near a pond or lake that you wouldn't want contaminated with pesticides. Insecticides containing the bacteria bacillus thuringiensis also work well and are not harmful to other wildlife. This spray should be applied while the cankerworms are still less than ½ inch in length for maximum effectiveness.
Use horticultural oils to kill cankerworms. Horticultural oil sprays will kill grown cankerworms, but are more effective in killing eggs. The oils will also drown larger cankerworms as they crawl up the trunk of the tree, preventing them from laying eggs. Thoroughly soak the tree trunk with the oil with a 2 to 3 percent dormant mixture from the pest control section of your local garden supply store. However, reduce the ratio on trees that bloom in the spring.
Prevent cankerworms from destroying your trees by using repellants. Using a repellent will keep cankerworms away from your trees and shrubs so you won't need to use harsh chemicals. Spray hot pepper oils, garlic extract and neem oil on the tops and bottoms of the leaves on your trees and shrubs. These natural repellents will safely keep cankerworms away.