The Disease Triangle

With the weather we have been having in our area, plant disease is a major concern for all producers. We have a high risk of aschocyta developing in peas. Sclerotinia stem rot is a disease that can devastate canola. Leaf disease can be a major factor when looking a cereal production. With all these diseases, it is critical that the disease triangle is understood. All elements of the disease triangle must be present for any disease to develop. Know what the factors are for your farm. The first component of the disease triangle is that you must have a susceptible host. This means that the plant that could be infected by the disease must be in the right stage and be the right plant. Not all diseases affect all plants. Some diseases only affect plants at certain stages. Some plants are only susceptible to specific diseases when they are in a stressed state like having waterlogged roots or having poor fertility. Growers must understand what it takes to help the plant develop resistance to a disease. Developing plants that are not susceptible to disease through plant breeding or proper management is the goal of many agronomists. If this cannot be done, the use of fungicides becomes the only option. They are costly and not the first choice of producers. The second component of the disease triangle is there has to be a conducive environment for the disease to develop. This means that there has to be the right amount of moisture, the right temperatures, the right soil conditions or the right humidity for a disease to develop. If these factors are not present, the disease will not develop. The conducive environment is part of the disease triangle that producers must understand and watch. If the conditions are right, this means that corrective action should be taken. If environmental conditions are not right, that means that applying control measures could be a waste of time and money. The third component of the disease triangle is that the pathogen must be present. There are practices that can avoid disease pressure. Clean seed, proper crop rotation and weed control are all factors that a producer can control and will reduce or eliminate the presence of a pathogen in the field. These are the free control measures and must be looked at by all producers. With most of the diseases that we deal with in this area, there are ways that we can reduce or eliminate the presence of pathogens in our fields. Producers must plan so that the pathogen is not present in excess levels in their fields. The disease triangle is something that all producers should understand. By understanding that the pathogen must be present, that the environment must be conducive to disease development and that having a host for the disease are all essential in the development of the disease, a strategy for disease control on the farm can be developed. Setting this strategy up for your farm is a must. Talk to your agronomist about what you can do to develop your strategy.


By Dave Cubbon, P Ag