Some soilborne pathogens can have a devastating effect on the economic viability of crops. Thankfully, soil health systems have been shown to help suppress plant pathogens. Below are some facts about soilborne pathogens and how soil conditions affect them.
- Soilborne pathogens cause seedling, vascular, and root rot diseases. Typical diseases result in visible lesions, rots, and wilts. Plant pathogens include fungi, oomycetes, nematodes, and viruses.
- Soilborne pathogens are specific to certain crop species and are generally rare in natural, unmanaged systems.
- Pathogens are not uniformly distributed through the soil profile and exist in microhabitats. This means the existence of a pathogen in soil does not necessarily mean plant disease will occur. However, higher loadings of pathogens in soil increase the likelihood of infected plants.
- Soilborne plant diseases are most severe when conditions are poor (e.g., inadequate drainage, poor soil structure, low organic matter, high compaction). Their presence is not only influenced by inherent soil properties, but also by climate and agricultural management.
- Pathogen survival in soil is tied to their ability to form vegetative structures that can survive for long periods. When environmental conditions are suitable, and a pathogen compatible host is present, vegetative structures germinate and penetrate below ground plant organs. After the death of the plant from disease or agronomic termination, “resting” pathogens contained in plant residues are returned to the soil surface.
How Soil Health Management Practices May Help
- Soil health management practices help alleviate poor conditions, therefore in general are perceived to reduce soilborne plant diseases.
- Additions of composted materials hold promise for suppressing plant pathogens (~50% success rate); however, mechanisms for successful suppression remain unknown.
- Conservation tillage leaves residue on the surface which breaks down at a slower rate than if incorporated during tillage events. This can allow pathogens to survive in the residues for extended periods. However, most problems identified with conservation tillage were observed in monoculture systems. Increases in plant disease are generally not found in reduced tillage systems with diverse cropping rotations and/or the use of cover crops.
- Crop rotations can break up the host-pathogen cycle. Any crop species that is not a host to the same pathogens can be useful in reducing pathogen loading in soils. However, some pathogens can survive for multiple years in the soil prior to infecting a host plant.
- The use of cover crops can help suppress pathogens. For example, crops in the brassica plant family (broccoli, turnip, radish, canola, rapeseed, and mustards) produce compounds that break down into volatile toxins that can suppress soilborne pathogens.
In terms of soil health management studies, disease suppression is commonly measured as disease reduction in the crop based on the implementation of soil health management practices. However, no soil health management practice consistently suppresses disease.
Pathogens are generally contained in low concentrations in soil, making direct quantification difficult. Recent advances in genomics provide finer details of pathogen loading and activity in soil. The incorporation of genomic techniques aims to predict disease rates based on genomic measurements of pathogens in soil.