Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

What borers damage trees and shrubs?

Several woody plants are subject to attack by insects that tunnel or bore into stems, branches, shoots and roots. These insects, called borers, kill branches and eventually can kill the entire plant. They are usually the larval or worm stage of a beetle or moth. In Missouri, Austrian pine, scotch pine, honeylocust, white birch, lilac, ash, privet, fruit trees, dogwoods, oaks and maples are the most common woody plants attacked by borers.

The first indication of borer attach is usually some dieback or thinning of the tree. Sawdust, frass, gumosis or sticky accumulations of sap, or holes in the bark are also indications that insects have invaded the woody portions of the plant. On birch trees the bark may appear lumpy.

Plants under stress are more susceptible to borer attach than are healthy ones. Stress may be due to an improper planting site, drought, construction or mower damage, or other unfavorable conditions. Healthy trees attract fewer insects and can withstand some borer activity. Therefore, your first line of defense is to maintain healthy plants.

Many borers are secondary pests. They attack trees that are already dying from other causes. Controlling these borers will do little to solve the primary problem of the tree. Consider anything that will improve the health of the tree such as proper fertilization and adequate watering, especially during dry spells.

After borers tunnel into the bark, some can be controlled by pruning out the infected parts, by crushing them with a flexible wire inserted into the hole, by probing with a sharp knife, or by injecting an insecticide into the hole. Your local nursery has insecticide products for this purpose. Pruning out weakened branches in which borers like to lay their eggs can also help reduce borer problems.

Chemical sprays can be used to prevent infestation, but before doing this, seek professional help from an arborist. Chemical sprays are generally only effective during the egg-laying period and as the larva hatch, before they have entered the bark. Consequently, timing is critical. Applied too early or too late you will just be wasting time and money and placing unneeded chemicals into the environment. To emphasize again, your best defense is to maintain a healthy plant and prune out weak or infested branches as they appear.