Cultural tactics are typically inexpensive and easily implemented preventative measures that are designed to avoid pest problems altogether or minimize pest injury.

• A cultural control may be as simple as keeping plants healthy and stress-free (e.g. irrigation during drought, etc.). Many plants are predisposed to pests when stressed.
• Other commonly used cultural controls include crop rotation and removal of infested plant material to reduce the chance of future pest problems.
• Examples of cultural controls used to manage common scab on potato, caused by the bacterium, Streptomyces scabies:
  • Rotation—common scab is a soilborne disease and rotating potatoes to another field or garden plot may solve the problem.
  • Amend soil with organic matter—common scab is more severe in light, sandy soils that dry rapidly. The addition of decomposed organic matter can improve the water-holding capacity of the soil.
  • Maintain adequate soil moisture, when practical, from 4 to 6 weeks after planting, to reduce tuber infection by the bacterium.
  • Check soil pH and adjust to 5.0 to 5.5. This pH inhibits development of common scab, while still favoring good potato production.
  • Purchase certified disease-free tubers, to avoid introducing the common scab bacterium into soil.

Physical tactics —examples of physical controls include cultivating weeds, plowing under infested crop debris to kill pathogens and using row covers to exclude insects from crops.

Resistance—when resistant varieties are available they are a first line of defense against pests.

• Plants may be naturally disease-resistant to a certain pest or many pests, or be bred or genetically modified for pest resistance. For example:
  • Certain species of trees commonly used in the home landscape are prone to pest problems, whereas other species are relatively pest-resistant and trouble-free.
  • Certain tomato varieties have resistance to the fungal vascular diseases, Fusarium and Verticillium wilt.
  • Resistant plants may be produced by genetic modification (transgenics). Examples of this are the Bt-transformed crops, which have been used in commercial production since 1996. These plants were genetically modified with genetic sequences from other organisms to produce proteins that are toxic to certain insects.

Monitoring and Scouting—growers should monitor or scout plants closely for signs of pests and use thresholds or forecasts, when available, to determine when control tactics are warranted.

• Researchers have developed economic thresholds for certain agricultural pests. This direct assessment method is mostly applicable to pests that can be counted, such as insects or nematodes. An example of this are the thresholds developed for soybean aphid. Methods for assessing populations of these aphids in soybean fields have also been developed to rapidly determine whether or not aphid populations have reached the economic threshold (i.e. an insecticide application will be of benefit).
• Indirect assessment methods, such as the use of sentinel crops or forecasting models, are useful for some plant pests. For example, sentinel plots were used to detect Asian soybean rust in the United States in 2005. Sentinel plots serve as an early warning system that alerts extension specialists and growers that a pest is present and control tactics may be warranted.
• Additionally, forecasting models are useful for certain pests that are carried by air currents and/or whose development is greatly influenced by moisture, temperature, atmospheric conditions, etc.
  • Forecasting models have been developed for certain pests/crops and are generally used by commercial growers.
  • Link to the North America Plant Disease Forecast Center.
• Disease severity and/or incidence are also useful for certain pests/crops when evaluating whether a control tactic will be beneficial. For example, the number of leaf spots on plants may be used to determine whether or not a fungicide application will be of benefit.
• Complex modeling systems have been developed for high value and/or large scale production crops. These computer-driven modeling systems analyze many parameters, such as temperature, moisture, plant varietal characteristics, yield data, effect of weather on pest populations and pesticide efficacy, cost of control tactics, etc.

Biological tactics employ naturally antagonistic organisms to control pests.

• Examples of biological controls include predatory or parasitic insects that kill pests.
  • Introduction of beneficial microbes into the soil to reduce populations of pathogenic microbes is a example of a biological control.
  • Promoting the naturally-occurring biodiversity of microbes, insect populations, etc. may also be considered a biological control. This type of tactic would be classified as preemptive or preventative. The addition of organic matter the soil is one example of a method to promote a biologically diverse microbial soil population, which may suppress pests.

Chemical controls—In the absence of adequate cultural tactics, resistant varieties, etc. or when other management tactics prove inadequate, chemical controls may be necessary. However, when chemical controls are deemed necessary, they are used in conjunction with as much information about the agricultural complex of the host, pest and environment, as is available, and used in a manner to minimize associated risks. Therefore, a chemical is applied only when it has been determined to be warranted (e.g. for agricultural crops when the application of a chemical control will result in an economic benefit).

• For example, in 2004, the fungal disease, Asian soybean rust, appeared in the United States for the first time. Since no resistant soybean varieties or other methods were available for acceptable levels of control of this potentially devastating soybean disease, the use of fungicides was the only control measure available. However, research information on both this disease and other rust diseases yielded important information about its biology, movement, environmental conditions favorable for disease development, and its development on soybean during different soybean developmental stages. All of this information was used to develop decision-making keys for management of Asian soybean rust. Growers were informed of:
  • The disease incidence level in the field, above which a fungicide treatment would be of no economic benefit.
  • The developmental stages of the soybean at which fungicide treatment would be of no benefit.
  • Application equipment and methods for optimizing fungicide applications for control of Asian soybean rust.
  • Additionally, a preliminary forecasting system was developed to alert growers and other stakeholders to intensify scouting efforts or to aid in decision-making regarding fungicide applications.
• Chemicals are classified as high risk or low risk (i.e. less potential to for negative health and environmental effects). The trend in registration of new chemicals by EPA has been toward registration of low risk, rather than high risk chemicals. Pesticides that are non-toxic or less toxic (soaps, oils, desiccants) are preferable to more toxic chemicals in terms of movement along the IPM continuum.
• Certain chemicals (e.g. ones that are generally not broadly toxic, but toxic in a very targeted manner) are at risk of development of resistance. This means that the pest population for which the chemical is targeted may lose their vulnerability to the chemical. The result is that the chemical is no longer effective and becomes useless. Chemicals prone to resistance development are typically lower risk (i.e. less potential to for negative health and environmental effects), since their toxic effect is targeted very specifically to certain characteristics of certain organisms, rather than broadly toxic to a large range of organisms. Use of a resistant-prone pesticide requires careful consideration and proper use to avoid development of resistance in the pest population.
• Another distinction to note is biorational pesticide versus conventional pesticide.
  • According to the EPA, biorational pesticides pose minimal risk to the environment, degrade quickly, leave minimal residue, are safe to handle, and relatively small quantities are required for effective control. Examples of biorational pesticides include growth regulators, oils, soaps and living microbes.
  • An example of biorational pesticide use: Through funds from a Strategic Agricultural Initiative Grant to Tennessee State University, researchers demonstrated control of the fungal disease, powdery mildew, on nursery crops using biorational controls (the product,  Armicarb [biocarbonate salt] and brandname household soaps (Palmolive, Ajax and Equate). A weekly application of each of the biorational control products controlled powdery mildew as well as conventional fungicides commonly used by the nursery industry. Read more about this research project.

Regulatory tactics, such as the emergency federal order to restrict movement of nursery stock from portions of California, Oregon and Washington, are of increasing relevance due to the increase in the global trade of plants, wood products, and other potentially pest-infested products.

E. Bush, last updated 12/19/05

Virginia Cooperative Extension - Virginia Agriculture & Experiment Station