Category 100: General Farming APPENDIX – Principles of Pest Management

Principles of Pest Management

The Decision Making Process

You must make a series of decisions to effectively plan and carry out a pest management program. Perhaps the least effective approach is to rely solely on immediate responses to problems as they arise; at that point, you usually must take direct action, with the use of pesticides often being the only option. We outline the principal elements of your decision-making process below.

Detection and Monitoring

We cannot overemphasize how important it is that you monitor for and detect pest infestations or conditions that lead to pest problems before a problem develops. If you don’t, control will likely be more costly, less effective, and perhaps too late to prevent damage.

To detect pests early, scout crops frequently, be familiar with the common pests in your area, and know the crop’s growth characteristics well enough to recognize abnormalities (e.g., disease symptoms).


You must identify an organism to determine whether it might be a pest and, if so, to decide whether and how to control it. You usually need to identify a plant disease based on symptoms rather than on the actual pathogen. A poor identification can lead to an unnecessary release of a pesticide into the environment and a waste of money.


Identification is only one tool. Once you have identified a pest, you can get information regarding its biology. Knowing the pest’s life cycle, and how it relates to environmental conditions, is essential in determining if and when a problem might occur and when control measures would be most effective. It makes sense to direct control efforts against the most vulnerable stages of a pest’s life cycle.

Economic Significance

Almost any level of infestation warrants control for some pests. For others, control is warranted only if you believe they will cause economic damage. Economic damage is the amount of injury that justifies the cost of control. It is different from biological damage, which frequently occurs without causing economic loss. Simply put, you gain nothing if the cost of control is greater than the dollar loss caused by the pest.

It is not easy to predict whether economic damage will occur. You need to consider the pest population; your geographic location and environmental conditions; the variety, growth stage, and value of the crop; and the cost of control.

The population density at which a pest will cause economic damage is the economic injury level (EIL). Obviously, you want to maintain pests below this level. The economic threshold (ET), also called the treatment or action threshold, is the population density at which you should apply control measures to prevent the pest from reaching the EIL. Note that the ET is usually not the level at which you first notice the pest damage.

Selection of Methods

If you conclude that control is necessary, the next step is to decide how to manage the pest. To make the best decision, become familiar with all available methods and evaluate the benefits and risks of each. The methods chosen must be effective, practical, economical, of minimal hazard to people and environmentally sound.


It is extremely important to evaluate the results of a management program. Tell your customer what to watch for and that some control methods do not yield immediate results. If a treatment did not control the problem alternative methods or different chemicals may be needed, the inspection may have been inadequate, or the treatment may not have been thorough enough. Record the evaluations for future reference; records can save you from repeating a past mistake or remind
you of a successful strategy you used in the past.

Methods of Pest Management

We will not discuss, in depth, the various methods of pest management; we will deal with them more fully in later appendices. Our intent here is to give you an overview of the alternatives available and to present some characteristics and
examples of each.


If a pest is completely or nearly absent from a site, do what you can to keep it out. It is often easier to prevent a pest from becoming established than to have to deal with it on a continual basis if it does. Steps that you can take to prevent pests from infesting a site include:

  • Using only certified seed so as not to inadvertently plant weed seeds along with your crop,
  • Purchasing healthy livestock, and
  • Making sure that any soil (which may contain nematodes or soil fungi) is cleaned off of application equipment before it enters the site.

Sanitation and Exclusion

Sanitation is a key to rodent and bird control. Sweep up spilled grain and keep garbage cans or other refuse containers tightly closed to eliminate possible food sources. Likewise, proper manure management will help reduce fly problems. Rodent-proofing grain storage areas is a way of excluding a pest from a site.

Resistant Varieties

Resistant crop varieties have inherent defenses against pests. The degree of resistance to a given pest can range from slight to nearly complete. Note that a resistant variety is resistant to only one or a few pests, never all pests. Resistant does not mean immune. While a pest may cause some damage to a resistant plant (though less than to a fully susceptible one), it cannot damage a plant that is immune to it.

Tolerant varieties produce well despite being susceptible to a pest. Beware, however, that pest populations will increase during the season and may pose even more of a problem the next year.

Mechanical Control

Tillage and cultivation are both effective in controlling germinating weed seedlings. Tillage can also help control some insects and plant pathogens by burying them, turning under crop debris that can serve as a habitat, or exposing soil organisms to desiccating conditions on the surface of a field. Rodent traps are another example of mechanical control.

Cultural Control

Cultural control includes practices designed to optimize growing conditions for the crop and/or create unfavorable conditions for the pest. Basically, anything that helps the crop itself will also help the crop fend off or successfully compete with pests. Proper plant density, fertilization, irrigation, and site preparation all help a plant to grow well. As with most organisms, plants are less able to withstand pests and diseases if they are under physiological stress (e.g., do not receive enough

Other crop management practices, such as crop rotation and the timing of planting and harvesting, can help avoid pest problems. Pest infestations can become devastating if a susceptible crop is grown year after year on the same land. Rotating to other crops may partly solve the problem by depriving the pest of a food source.

Biological Control

Biological control focuses on maximizing the effects of the natural enemies of pests. Thousands of species of insects, mites, nematodes, and pathogens feed on or parasitize pests. You can capitalize on this natural benefit by preserving appropriate habitats in areas surrounding your fields and, when using chemical control, using pesticides that have as little impact as possible on beneficial species. Keep in mind that for biological control to be effective, there needs to be a sufficient pest population for the natural enemies to prey upon. As with pesticides, therefore, we cannot expect biological agents to eradicate a pest.

Chemical Control

Pesticides are often used in combination with the other pest management techniques we have already discussed and should be the last alternative in most management programs. They act quickly and there are typically a number of effective products available for almost any pest situation. When an infestation is severe and damage is obvious or imminent, pesticides can provide the quickest and most effective solution.

There are also disadvantages to pesticide use. The primary concern is toxicity. Each pesticide poses at least some risk to the person using the pesticide and people who enter a site after it is treated. Pest populations may also develop resistance to pesticides, making control more difficult. Finally, pesticides usually provide only temporary solutions; a change in other management practices (e.g., crop rotation) may be necessary to prevent future problems.

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