Chapter 12

Plant Disease Management for Organic Crops

(book excerpts)

All species of plants, wild and cultivated a like, are susceptible to disease. The occurrence and prevalence of plant diseases vary from season to season, depending on the presence of the pathogen, environmental conditions, and the crops and varieties grown. Some plant varieties are particularly subject to outbreaks of diseases; others are more resistant to them. Plant diseases create challenging problems in commercial agriculture and pose real economic threats to organic farming systems. Plant pathogens are constantly changing and mutating, resulting in new strains and new challenges to growers. Also, given the local, regional, and international movement of seed, plant material, and farming equipment, new and introduced pathogens periodically enter the organic farming system to cause new disease problems. Disease management is complicated by the presence of multiple types of pathogens. For any one crop the grower must deal with a variety of fungi, bacteria, viruses, and nematodes. If a plant pathogen is present, the severity of the disease it causes will be determined by the level of infestation, by environmental conditions, and the susceptibility of the crop. Organic farmers rely primarily on preventive, cultural, and integrated methods of disease management and to some extent biological and chemical control measures too. It is unlikely that all diseases can be avoided by utilizing any one of these management strategies alone. However, the damage of many plant diseases can be greatly reduced by the integration of these practices. 

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