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All plant diseases result from a three-way interaction between the host, the pathogen and the environment. An epidemic develops if all three of these factors are favourable to disease development. Therefore, disease can be controlled by manipulating one or more of these factors so that conditions are unsuitable for replication, survival or infection by the pathogen.

The pathogen can be manipulated by excluding or reducing inoculum available to infect plants. If a particular pathogen is not present in an area then attempts can be made to prevent its introduction. Quarantine regulations govern the introduction of plant material from high-risk areas. Seed certification schemes also reduce the risk of introducing a new pathogen, and propagating material can be treated to kill any inoculum that is present, before it is introduced to a new area. If a pathogen is already present in an area, efforts to eliminate or reduce the amount of inoculum present are the only option. Elimination of an existing pathogen is usually not successful, but there are a variety of methods, such as crop rotation, chemical and physical treatment and trapping, that can effectively reduce the amount of inoculum available. The nature of the pathogen can have a significant impact on the management of its disease. Link to Disease Development.

Link to Fungal Biology - Fungicides

The host can be manipulated by increasing its resistance to disease. This can involve breeding or selecting plants for genetic resistance to a specific disease, or by applying chemicals, such as fungicides, that prevent or halt infections in the plant.

The environment can be modified so that it is suitable for plant growth but not for disease development. For example, improving soil drainage, changing the time of sowing, reducing the density of plants in a crop or changing irrigation practices can all produce conditions unfavourable to particular diseases, while maintaining conditions suitable for the growth of the plant.

Any decrease in the amount of initial inoculum, the rate of disease increase of the time available for development, will cause a decrease in the amount of disease. Therefore, management strategies look at reducing one or more of these factors in order to reduce the amount of disease. The initial amount of inoculum can be controlled by quarantine practises and preventative treatments. The time available for disease development can be reduced in some kinds of crops by harvesting before the disease has developed to epidemic proportions. The rate of disease increase can be reduced by mixing plants that are not all susceptible to the same strain of pathogen, by applying preventative chemical treatments, and by changing the environments the host and pathogen are exposed to, for example, by changing planting dates, crop density or irrigation practices.

Integrated pest management uses all suitable techniques that complement each other with the aim of keeping pest populations below the threshold at which economic damage occurs. This approach also aims to avoid the problem of pests developing resistance to widely used insecticides. In integrated pest management, resistant crop varieties might be used in conjunction with chemical treatment, crop rotation and manipulation of the environment. Multiple approaches to disease management are particularly useful when the disease cycle is not fully understood.


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