Part 1, Section 11: Organic Crop Production
Organic Crop Production
Pest Management in Organic Systems
Diseases
Disease Management for organic field crop production centers on several tools of plant disease management, including host resistance, exclusion, crop rotation, cultivation, and plant disease diagnosis. 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 tools. The sections below provide more information regarding these management options.
Host Resistance
Many plant diseases can be effectively managed be selecting varieties that are naturally resistant to specific disease causing organisms. Host resistance can be either partial or complete. Varieties with complete resistance are completely immune to attack by a specific pathogen or a “race” of the pathogen population. In contrast, varieties partial resistance may still develop symptoms of the disease, but the disease will progress more slowly than in susceptible plants. The use of host resistance can be highly effective in reducing disease pressure. Knowing the pathogen or race of pathogen you wish to control is necessary to ensure that host resistance is targeted to the most important disease issues. Contact your seed dealer or Penn State Cooperative Extension for more information about resistant varieties.
Exclusion
Exclusion is the practice of keeping materials and objects that may be contaminated with a pathogen out of the production system. Some diseases are spread through seed, so it is important to purchase seed from a reputable source. Although some seeds are designated as “pathogen-free seed,” it is impossible to be certain that a seed lot is entirely free of all pathogens. Other considerations include cleaning tools and equipment to avoid spreading diseased tissue and pathogens between fields, especially if you know of problems in one field (e.g., white mold of bean or late blight of potato or tomato).
Crop Rotation
A large number of the pathogens that cause disease in field crops survive in association with crop residues left on the soil surface. A diverse crop rotation can contribute to the reduction of pathogens through lack of susceptible hosts in the field and allow for crop residue harboring pathogens to decompose. During the decomposition of the crop residues, the disease-causing organisms will be forced to compete with other organisms for limited resources (for example, food, water, and space). The pathogen population will also decline as it is attacked by naturally occurring pathogens of that organism. Rotation to a non-host crop for 2 to 3 years is desirable.
Cultivation
Tillage can also be used to hasten the decomposition of crop residues and decline of a pathogen population. In this case, the goal is to bury crop residues or place them in contact with the soil so that they are quickly colonized by organisms involved with residue decomposition and exclusion of the disease-causing organisms. However, many fields in Pennsylvania are not suitable for tillage because of soil erosion concerns, and producers should carefully evaluate the potential risk of erosion on their farm.
Plant Disease Diagnostics
The first step in disease management is proper diagnosis of the pathogen and disease. As soon as certain symptoms become a problem in the field, it is important to determine the pathogen and disease in a timely manner to help reduce spread and potential impact. Once identified, imformation about the disease can then be used to best control the disease and impact on yield and quality. Infected plant samples can be sent to the Plant Disease Clinic, 220 Buckout Lab, University Park, PA 16802 for proper diagnosis.