Diseases
Organic Crop Production
Pest Management in Organic Systems
Diseases
Disease management for organic field crop production should focus on several aspects of plant disease management, including host resistance, site selection, 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 practices. The sections below provide more information regarding these management options.
Host Resistance
Many plant diseases can be effectively managed by 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 with partial resistance may still develop symptoms of the disease, but the disease will progress slowly and have less of an impact when compared to 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 office for more information about resistant varieties.
Site Selection
Soil and environmental conditions can play a key role in disease development. Prior to planting a crop, it is important to understand what soil or environmental conditions may exist that can exacerbate disease development. Issues such as compacted soils or poor soil drainage can lead to root diseases in seedlings and mature plants. Low-lying areas or soil located next to a forest or river can have extended periods of dew or fog, which is a key factor in the development of many foliar diseases of crops. Optimum fertility and soil pH will also help ensure plant health and the ability to defend against pathogens.
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 soybean or Phytophthora root rot).
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 (i.e., food, water, and space). The pathogen population will also decline as it is attacked by naturally occurring pathogens of that organism. Rotation to a nonhost crop for 2 to 3 years is desirable.Proper weed control is also important since weeds can act as alternative hosts to some crop diseases.
Cultivation
Tillage can also be used to hasten the decomposition of crop residues and encourage the decline of a pathogen population. In this case, the goal is to bury crop residue or place the residue in contact with the soil so that they are quickly colonized by organisms involved with residue decomposition. These soil microbes will compete with the disease-causing organisms, reducing their populations. 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
An important 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 causal agent in a timely matter to help reduce spread and potential impact. Once identified, information about the disease can then be used to determine the best control measures and reduce the impact on yield and quality. Infected plant samples can be sent to the Plant Disease Clinic, 220 Buckhout Lab, University Park, PA 16802 for proper diagnosis.
Applying Control Methods
Many products are available that help prevent fungal and bacterial diseases from developing. Products may include sulfur, lime, copper, or combinations of two or more. It is important that the product you use is certified for use on organic operations. For a list of products, go to www.omri.org/simple-opl-search/results/fungicide.
