Forest Health > Insects and Diseases publication
Principles of Control
SPRAY! Unfortunately, this is the most common response of laymen desiring control of an insect or disease damaging their trees. It is true that pesticide applications may be an acceptable and effective control in certain situations. Yet, it is important to realize that pesticide application is only one of an array of control methods available for preventing or suppressing insect and disease activity in trees.
In many cases involving insects or diseases in trees, the use of a pesticide (fungicide, insecticide, miticide) can't be justified economically, legally or biologically. In fact, for many tree pest problems pesticides just don't work. Thus, the desired result is often better achieved through the application of one or more alternative control methods.
Today, pest management specialists, such as entomologists and pathologists, expound the virtues of INTEGRATED PEST MANAGEMENT (IPM). This term is actually a rephrasing of what was previously considered to be a common sense approach to the control of insect and disease pests. IPM does not promote any one control method above another, or to the exclusion of all other methods. Instead, IPM advocates the employment of those control methods which are most effective, efficient, and economical, as well as biologically, ecologically, and sociologically sound. One pest management problem may require one control method. Another may require a totally different approach. Others may be best handled by a combination of methods.
introduction to some general principles and methods of pest control:
Behavioral Method
Behavioral control generally employs synthetic chemicals, which are similar to natural chemicals utilized by insects in their interactions with trees (insect pheromones and host tree odors), to disrupt behavior on which insects normally depend to successfully mate or locate food or habitat. Repellants, confusion or inhibition chemicals prevent or minimize infestation of susceptible trees. Attractants are often used to lure insects to glue or poison traps. Pheromone-baited traps are currently employed as useful survey and detection tools for insects such as the gypsy moth and the Nantucket pine tip moth. Research may soon provide a method for using natural chemicals, inhibitory to pine bark beetles, to protect southern pines.
Biological Method
Biological control is the use of beneficial or harmless organisms to control or suppress a pest organism. Biological control has two aspects: natural and classical. NATURAL BIOLOGICAL CONTROL is deceptively important in the day-to-day suppression of insects and diseases that would otherwise cause serious damage to trees. Most pests native to North America have an abundance of natural enemies that serve a vital role in keeping pest populations at innocuous levels. Biological control agents or natural enemies include mammals, birds, insects, mites, spiders, amphibians, reptiles, fungi, bacteria, nematodes and viruses. These agents function as predators, parasites, pathogens, antagonists, and/or competitors of pest organisms. In contrast, CLASSICAL BIOLOGICAL CONTROL involves the introduction of natural enemies into specific areas to control a pest which has previously been introduced inadvertently, and is a problem because it is not controlled by native biological or environmental factors.
Typically, imported natural enemies are from the area of origin of the target pest. An important development in the biological control of insects entails the mass production and application of parasitic microorganisms (bacteria, viruses, nematodes) which attack only one or a few related insect species. These microorganisms are often very effective control agents and their apparent toxicity to man is minimal or none. Bacillus thuringiensis, a bacterium, is widely used around yards and in commercial settings in control a number of caterpillars that feed on trees and other crops. The use of a competitive fungus to suppress annosum root rot activity in thinned pine plantations is an excellent example of biological control of a tree disease.
Genetic Method
The most familiar use of genetics for control of insects and diseases is the breeding and utilization of varieties (genotypes) of host tree species which are genetically less susceptible or more resistant to problem insects or diseases. For example, commercial forest industries currently cooperate with federal and state government agencies in the South to select, breed, and utilize pines which are resistant to fusiform rust. Another approach to genetic control of harmful pests is the introduction of genetically weak (avirulent) pest strains or varieties into pest populations which are normally damaging or aggressive (virulent). The assumption is that the results of interbreeding will eventually be a pest population that is less damaging than the original. This approach is showing promise in research efforts aimed at controlling the infamous chestnut blight fungus.
Regulatory Method
The fundamental objectives of regulatory pest control include preventing entry and establishment of foreign plant and animal pests, and the eradication, containment, or suppression of pests established in limited areas. These objectives are accomplished by a variety of means including (1) CERTIFICATION that plant materials being moved from state to state or country to country are pest free, (2) INSPECTION of nurseries and plant materials being transported to detect, identify, and control harmful pests before they are spread, (3) SURVEYS to detect and delineate infestations or infections of harmful pests which may have inadvertently been introduced into an area, and (4) the establishment and enforcement of QUARANTINES where necessary to prevent movement of dangerous pests. In Florida, the legal authority for the implementation of regulatory plant pest control calls within the jurisdiction of the Department of Agriculture and Consumer Services, Division of Plant Industry, headquartered in Gainesville.
Cultural Method
Cultural methods of pest control are many and diverse but are particularly applicable and effective in many situations. Generally, cultural control methods are practices which are good for trees and bad for harmful pests. Common practices include:
- SANITATION and HOST ERADICATION which involve removal and/or destruction of host material (leaves, branches, trees) infested with insects or exhibiting symptoms of diseases. This practice reduces the threat of spread and/or intensification of the problem.
- FERTILIZATION, or keeping trees well fed, often enables them to ward off a variety of pest problems.
- IRRIGATION, natural or mechanical, is important. Moisture deficiencies can render trees susceptible to a variety of insects and diseases. Note: overwatering can be just as serious as underwatering.
- ALTERNATIVE HOST ERADICATION means removal and/or destruction of alternate host plants not desired by the landowner, but necessary for the successful development of certain insects and diseases (especially applicable to various rust diseases caused by certain fungi).
- AVOIDANCE means prevention of insect and disease problems through practices such as planting nonsusceptible species and preventing injuries to existing trees.
- PROPER SITE SELECTION means planting trees in locations to which they are well adapted to avoid unnecessary stress, or planting trees on sites that are not conducive to pest activity.
- TIMBER STAND IMPROVEMENT involves aspects of other practices, but includes thinning forest stands to promote tree vigor and removing undesirable, pest infested or diseased trees.
- PROPER TIMING of forest and shade tree practices means planting, thinning, pruning and harvesting of trees at times when associated pest problems are less likely to cause serious damage.
- Use of CLEAN PLANTING STOCK, seeds and seedlings free of harmful pests, is a key element in preventing insect and disease problems from developing.
Physical and Mechanical Methods
Physical and mechanical controls are the oldest of all control methods. They differ from cultural methods in that they are employed directly against pests and are not a part of regular or preventive cultural practices per se. Physical and mechanical methods are particularly applicable to insect pests, and are employed to destroy pests outright, disrupt normal biological habits, or modify the environment to discourage pest activity. Some tools employed as physical or mechanical control include adhesives, sound, screens, or other barriers, traps, light, heat and refrigeration. Handpicking, brushing, crushing, or washing insect pests from infested trees are also physical or mechanical controls.
Pesticidal Method
Pesticides are chemicals specifically designed to kill or harm pests. Today, several hundred pesticides are available and are designed to address a wide variety of pest problems. However, each pesticide is applicable, either biologically or legally, to a limited number of pest organisms and sites. No one pesticide is applicable for all situations. Pesticides are poisons, and by their very nature require judicious and skillful use. In the hands of knowledgeable users, pesticides can be an important control method. All pesticide containers must have labels. READ THE LABEL!
Other sources of information
- Local Division of Forestry County Forester
- Local Cooperative Extension Office — county extension agent
- Pest Control Operators — private firms that will provide a service to directly control a problem as well as provide technical advice
- Leaflets — both the Division of Forestry and the Cooperative Extension Service provide concise publications that address a single pest or group of pests, and pesticide recommendations are usually listed and discussed where applicable.
Conclusion
All of these methods of pest control involve the concept of prevention. If all other words, concepts, and definitions are forgotten, remember PREVENTION. Many insects and disease problems affecting trees can easily be prevented. Unfortunately, they are not. Clearly, some pest problems are unavoidable. Trees that are properly cared for, however, are far less likely to fall victim to harmful pests than those which are neglected or abused.
BACK Bulletin No. 196-A | Printed October, 1983 | Contact the Forest Health Section |
