Systemic Acquired Resistance - What is it?

You may be hearing more and more about plant protection products known as SAR inducers or plant activators. What does this mean?

SAR, or systemic acquired resistance, products actually trigger or enhance the plant's natural defenses against infection. Although they may be labeled for control of plant disease, they do not have any direct activity on the fungus, bacteria, or other pathogen.

Plants have a natural resistance mechanism that is activated once an infection is initiated. You could think of it as an immune response like humans would have to an infection. This response can also be initiated by certain chemicals - by treating a plant with an SAR inducer, we are able to initiate the resistance response prior to an infection. Think of the response we have to a vaccination. We build up immunity without being exposed to the live pathogen. Of course, vaccinations are specific to a particular virus, while SAR is a broad-spectrum response. These chemicals use the plant's own biological pathways to prepare it for a stronger response against disease.

SAR products are used differently than fungicides or bactericides. They need to be applied before an infection occurs, as it takes time after treatment for the plant response to be activated to the point of effectiveness. They do not act directly on the pathogen, so they are used as part of a disease control program. Cultural practices (and fungicides or bactericides where possible) are still needed to prevent the pathogen population from building up.

SAR products do not offer control of all plant diseases. Research continues to uncover their most effective uses and how to use them in a pest management system. As these products come into use, it will be important to read and understand the labels and follow recommendations for optimizing their effectiveness.