Principles of Pest Control


A pest is anything that:

Types of Pests

Types of pests include:

Most organisms are not pests. A species may be a pest in some situations and not in others. An organism should not be considered a pest until it is proven to be one.

Pest Identification

Accurate identification is the first step in an effective pest management program. Never attempt a pest control program until you are sure of what the pest is. The more you know about the pest and the factors that influence its development and spread, the easier, more cost-effective, and more successful your pest control will be. Correct identification of a pest allows you to determine basic information about it, including its life cycle and the time that it is most susceptible to being controlled.

You must be familiar with the pests you are likely to encounter. To be able to identify and control pests, you need to know:

Pest Control

Any time you are considering whether pest control is necessary, remember:

Pest Control Goals

Whenever you try to control a pest, you will want to achieve one of these three goals, or some combination of them:

Prevention may be a goal when the pest's presence or abundance can be predicted in advance.

Suppression is a common goal in many pest situations. The intent is to reduce the number of pests to a level where the harm they are causing is acceptable.

Eradication is a rare goal in outdoor pest situations, because it is difficult to achieve. Usually the goal is prevention and/or suppression. In indoor areas, eradication is a more common goal. Enclosed environments usually are smaller, less complex, and more easily controlled than outdoor areas. In many enclosed areas, such as dwellings; schools; office buildings; and health care, food processing, and food preparation facilities, certain pests cannot or will not be tolerated.

Threshold Levels

Thresholds are the levels of pest populations at which you should take pest control action if you want to prevent the pests in an area from causing unacceptable injury or harm. Thresholds may be based on esthetic, health, or economic considerations. These levels, which are known as "action thresholds," have been determined for many pests.

A threshold often is set at the level where the economic losses caused by pest damage, if the pest population continued to grow, would be greater than the cost of controlling the pests. These types of action thresholds sometimes are called "economic thresholds."

In some pest control situations, the threshold level is zero: even a single pest in such a situation is unreasonably harmful. For example, the presence of any rodents in food processing facilities forces action. In homes, people generally take action to control some pests, such as rodents or roaches, even if only one or a few have been seen.

Pest Monitoring

In most pest control situations, the area to be protected should be monitored (checked or scouted) often. Regular monitoring can answer several important questions:

Monitoring of insect, insect-like, mollusk, and vertebrate pests usually is done by trapping or by scouting. Monitoring of weed pests usually is done by visual inspection. Monitoring for microbial pests is done by looking for the injury or damage they cause.

Monitoring also can include checking environmental conditions in the area that is being managed. Temperature and moisture levels, especially humidity, are often important clues in predicting when a pest outbreak will occur or will hit threshold levels.

Monitoring is not necessary in situations where a pest is continually present and the threshold is zero. For example, there is zero tolerance for the presence of bacteria in operating rooms and other sterile areas of health care facilities. In these situations, routine pest control measures are taken to prevent pests from entering an area and to eradicate any pests that may be present.

Avoiding Harmful Effects

Pest control involves more than simply identifying a pest and using a control tactic. The treatment site, whether it is an outdoor area or inside a structure, usually contains other living organisms (such as people, animals, and plants) and nonliving surroundings (such as air, water, structures, objects, and surfaces). All of these could be affected by the pest control measures you choose. Unless you consider the possible effects on the entire system within which the pest exists, your pest control effort could cause harm or lead to continued or new pest problems. Rely on your own good judgment and, when pesticides are part of the strategy, on the pesticide labeling.

Most treatment sites are disrupted to some degree by pest control strategies. The actions of every type of organism or component sharing the site usually affect the actions and well-being of many others. When the balance is disrupted, certain organisms may be destroyed or reduced in number, and others -- sometimes the pests -- may dominate.

Pest Control Failures

Sometimes you may find that even though you applied a pesticide, the pest has not been controlled. You should review the situation to try to determine what went wrong. There are several possible reasons for the failure of chemical pest control.

Pest Resistance

Pesticides fail to control some pests because the pests are resistant to the pesticides. Consider this when planning pest control programs that rely on the use of pesticides. Rarely does any pesticide kill all the target pests. Each time a pesticide is used, it selectively kills the most susceptible pests. Some pests avoid the pesticide. Others withstand its effects. Pests that are not destroyed may pass along to their offspring the trait that allowed them to survive.

When one pesticide is used repeatedly in the same place, against the same pest, the surviving pest population may be more resistant to the pesticide than the original population was. The opportunity for resistance is greater when a pesticide is used over a wide geographic area or when a pesticide is applied repeatedly to a rather small area where pest populations are isolated. A pesticide that leaves a residue that gradually loses its effectiveness over time will help select out resistance. Rotating pesticides may help reduce the development of pest resistance.

Other Reasons for Failure

Not every pesticide failure is caused by pest resistance. Make sure that you have used the correct pesticide and the correct dosage and that you have applied the pesticide correctly. Sometimes a pesticide application fails to control a pest because the pest was not identified correctly and the wrong pesticide was chosen. Other applications fail because the pesticide was not applied at an appropriate time -- the pest may not have been in the area during the application or it may have been in a life cycle stage or location where it was not susceptible to the pesticide. Also remember that the pests that are present may be part of a new infestation that developed after the chemical was applied.

Philip G. Koehler, University of Florida
Robert A. Belmont, Florida Pest Control Association

This file is part of the UF/IFAS Basic Pesticide Training manual (SM-59) which is intended to provide intermediate training to pest control operators. The manual was adapted from a larger manual, Applying Pesticides Properly, which was developed by Ohio State University in cooperation with the Cooperative Extension Service, U.S. Department of Agriculture, and the Office of Pesticide Programs, U.S. Environmental Protection Agency.

Published: March, 1998