Stress Encourages Pest Problems
Borers typically attack trees or shrubs when they are already weakened by some other problem. They contribute to its decline. A tree, shrub or woody vine may be old or suffering from air pollution. It may have root rot or be living in compacted soil with little or no organic material in it. Often, a tree that has experienced storm damage is invaded by borers when proper repairs are not made. Plants that have suffered severe drought are often invaded by borers the following year.
Normally, healthy trees and shrubs can repel a borer attack with sap resins as the insects try to bore into the wood. So if the causes of stress that is draining the vigor from the plants can be identified and corrected the afflicted plant may be able to defend itself once again.
Some Causes Of Plant Stress
Some causes of stress in trees and shrubs that reduce their ability to withstand borer attacks include:
Too much or too little light or moisture.
Inappropriate plants for the climate or local environmental conditions such as pollution, salt spray or wind.
Excessive use of nitrogen-rich fertilizer, which encourages too much weak, leafy plant growth.
Drastic pruning of trees or shrubs, which stimulates growth of succulent suckers (side shoots) and exposes other parts of the plant to sunscald.
Use of broad-spectrum pesticides against other pests which also kill off the borer’s natural predators and parasites.
Transplant shock which makes plants vulnerable to borers for a few days to a week.
Old age; nearby construction; neglect; untreated injury.
Other Conditions That Foster Borers
Borer populations are normally controlled by various kinds of birds and beneficial insects living in healthy home landscapes that host a diversity of plants and wildlife. However, frequent use of broad-spectrum insecticides kills insects indiscriminately and the beneficial insects that prey on pests are eliminated along with them. Since pest populations rebound faster than those of their natural enemies, the borers can establish themselves unmolested. When an insecticide product is necessary, choose one that is specific to the pest problem, if possible to avoid inadvertently killing off beneficial allies.