Each of those sub-objectives can also have sub-objectives, and so on, in a hierarchy that can consist of several layers of objectives.įor example, suppose that our general objective (goal) is to reduce the losses caused by potato late blight in a particular field. The most general objective, in order to be realized, will have several sub-objectives that first must be successfully accomplished. Each individual task, no matter how skillfully executed or how successful its outcome, will not advance progress toward the final objective unless it has a coherent relationship with all of the other necessary tasks. Any endeavor that requires a series of connected tasks for its completion also requires some kind of overall plan. The important point to remember is that countless human undertakings, be they military operations, political campaigns, football games, or any other kind of organized effort, have failed, despite flawless tactics, for lack of a sound strategy. What is a "strategy" at one level of focus could be called a "tactic" at another level of focus. Like the goals and objectives that they are intended to achieve, strategies and tactics tend to occur in hierarchies. The dictionary definitions for the two terms are similar, but generally speaking, an overall plan for reaching a particular objective is called a strategy, while the specific means for implementing a given strategy are called tactics. The problem is generally one of semantics rather than of fundamental disagreement over the important means of disease control. Strategies versus TacticsĪsk a handful of pest management experts to name the major plant disease control strategies, and you are sure to find disagreement. We need some means of assessing quantitatively the effects of various control measures, singly and in combination, on the progress of disease.įinally, the traditional principles of plant disease control tend to emphasize tactics without fitting them into an adequate overall strategy.ĭoes this mean that we should abandon the traditional principles? Of course not! We merely have to fit them into an appropriate overall strategy based on epidemiological principles. They also fail to show how the different disease control measures interact in their effects on disease dynamics. (See: Disease Progress.) Furthermore, considering that different diseases differ in their dynamics, they do not indicate the relative effectiveness of the various tactics for the control of a particular disease. Instead of plant disease control, we need to think in terms of plant disease management.Ī second shortcoming is that the traditional principles of plant disease control do not take into consideration the dynamics of plant disease, that is, the changes in the incidence and severity of disease in time and space. Indeed, we need not eliminate a disease we merely need to reduce its progress and keep disease development below an acceptable level. Plant disease "control" in this sense is not practical, and in most cases is not even possible. First of all, these principles are stated in absolute terms (e.g., "exclude", "prevent", and "eliminate") that imply a goal of zero disease. While these principles are as valid today as they were in 1929, in the context of modern concepts of plant disease management, they have some critical shortcomings. Therapy-cure plants that are already infected.Resistance-utilize cultivars that are resistant to or tolerant of infection. Protection-prevent infection by means of a toxicant or some other barrier to infection.Eradication-eliminate, destroy, or inactivate the inoculum.Exclusion-prevent the introduction of inoculum.Avoidance-prevent disease by selecting a time of the year or a site where there is no inoculum or where the environment is not favorable for infection.Traditional Principles of Plant Disease Control These "traditional principles", as they have come to be known, were outlined by a committee of the US National Academy of Sciences, 1968. Whetzel in 1929 and modified somewhat by various authors over the years, has been widely adopted and taught to generations of plant pathology students around the world. One such set of principles, first articulated by H. Following our discovery of the causes of plant diseases in the early nineteenth century, our growing understanding of the interactions of pathogen and host has enabled us to develop a wide array of measures for the control of specific plant diseases.įrom this accumulated knowledge base, we can distill some general principles of plant disease control that can help us address the management of new problems on whatever crop in any environment. Since the beginning of agriculture, generations of farmers have been evolving practices for combating the various plagues suffered by our crops.
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