Pest management in perspective

Laurie Litman

Pest management is another of those subjects that becomes more fascinating and less absolute the more you learn about it.

To consider this topic properly, we should begin at the beginning with a somewhat philosophical question: what is a pest? In reality, a pest is simply any organism—insect, fungus, plant, bacteria, mammal, etc.—that interferes with our plans or gets in our way. A pest is a nuisance, a problem, a blight, but it’s not inherently bad or evil.

Your response to any pest problem depends on your tolerance for the damage or nuisance. Before taking any action, you should stop and figure out what’s happening and decide whether you really need to do anything about it.

Most of the time, pest problems are manageable. Natural population fluctuations may cause a temporary increase in a pest population, but these are usually brought under control by a corresponding increase in predator populations. The checks and balances that have evolved in the ecosystem over time provide stability and generally don’t require any intervention on our part.

In many cases a pest situation is complicated by the existence of a pest complex, a number of pests that act in various ways on a tree. We see this in Oak Mortality Syndrome (see page 4) where numerous pests are found associated with diseased trees. One is the primary pathogen which is responsible for the disease; the others are considered secondary pests, they come in only after the tree is weakened and further the damage. When dealing with a pest complex, it makes sense to identify and control the primary pest or cause of the weakened trees.

Pest problems generally arise when something in the ecosystem changes—either the host becomes more susceptible or a pest more effective. It can be a natural occurrence like climatic change, the introduction of a non-native organism, or any number of other circumstances.

Stress is often at the heart of a pest problem. Healthy trees have natural defenses to injury and are much less likely to suffer from pest attack than those that are stressed. For this reason, the best strategy in dealing with pests is generally a proactive effort to keep your forest healthy.

One of the most important stress-causing agents is drought. Others include excessive rain, competition from other trees, air pollution, soil problems such as compaction, excess pruning, insect damage, etc. Knowing how to maintain the health of your trees and minimize stress is an integral part of pest management.

Non-native (exotic) pests are another cause of excessive pest damage, a problem that may accelerate with the current increase in global trade. Exotic pests are organisms that have escaped the predators and pathogens that keep them in check in their homeland. At the same time, our native species may lack the traits that confer resistance and therefore be highly susceptible to attack. For example, the pitch canker disease (see page 6) is caused by an exotic fungus that has found an extremely susceptible host in our native Monterey Pine. Luckily, a significant percentage (around 15%) of the pines have genetic resistance to the pitch canker disease. The fact that this resistance existed in the population in the absence of the pathogen is a mystery but it clearly demonstrates the importance of maintaining genetic diversity in forest populations. A diverse gene pool increases the odds of a population adapting successfully to new, potentially threatening, conditions in the environment.

When a pest problem does occur, it’s important to approach it in a thoughtful, knowledgeable manner. Integrated Pest Management (IPM) was developed as such an approach.

The first step in IPM is continuous monitoring of your forestland. You need to know what is normal and detect problems as early as possible. This includes identifying stressful conditions and mitigating them, encouraging natural control, and maintaining the health of the forest.

If a pest problem is detected, identification is necessary. There are books available as well as knowledgeable experts eager to help you identify or confirm a pest problem and offer advice.

Pest treatment can be expensive, and in some cases include the use of toxic chemicals, so a thorough evaluation is important before taking action. This evaluation involves looking at the potential damage and all alternative treatments in the context of your objectives for your forestland. This takes into account your tolerance level for the damage, the economic and environmental consequences of both the problem and various treatment options, as well as other variables. Often, the “no action” alternative is found to be the best, most appropriate action.

When treatment is considered necessary, the least toxic, least disruptive, long-term alternative should be followed with the goal being not to eradicate the pests but to keep damage at a tolerable level.

—for more information on IPM and pest control, contact your local UC Cooperative Extension Advisor or CDF Forest Pest Specialist.