Resistance management

Pesticide resistance

Pesticide Resistance is the ability of a pest to develop a tolerance to a pesticide. Pests (weeds, insects, mites, diseases, etc.) that become resistant to a pesticide will not be affected by the pesticide. When pests are resistant, it is more difficult to control the pest. Pesticide resistance develops when pesticides are used too often and when the same pesticide or similar pesticides are used over and over again. ​

Resistance management is an important concept for agricultural producers to understand and practice. Preventing or delaying resistance results in pesticides remaining useful for a longer period of time. It will also help to prevent crop loss due to pesticide failure.

How resistance develops

Resistance usually develops by genetic mutation and selection. Types of mutations can include: a change in processes in the pest that make the pesticide harmless, a change in the place where the pesticide enters the pest so it cannot enter, or a change in the behavior of the pest so that it avoids the pesticide. Resistant pests are selected when the pests reproduce. For example, in any pest population there may be some pests that will not be killed by the pesticide. When the pests that survive breed, some of their young will inherit the pesticide resistance. These pests will not be affected the next time the pesticide is used. If the same pesticide, or pesticides with the same mode of action are applied repeatedly, pests that are resistant will continue to increase. With each generation, the pest population becomes more difficult to control with the same pesticide. 

Managing resistance

Reduce the development of pesticide resistance by:

• Only using pesticides when necessary
• Alternating pesticides in different resistance management groups
• Using tank mixtures or pre-mixes of pesticides in different resistance management groups
• Monitoring to make sure pesticides are applied at the most effective time
• Using the recommended application rate. Avoid using low rates with marginal pest control.
• Getting complete coverage so all plant parts receive the proper pesticide dose
• Using selective pesticides that break down quickly
• If the pesticide doesn’t work, do not re-treat with a pesticide in the same group
• Do not rely only on pesticides.  Practice Integrated Pest Management (IPM) using other control methods such as:
  • Pest tolerant or resistant plant varieties
  • Cultural or mechanical controls
  • Biological controls
• Crop production Guides provide information on IPM for specific crops and pests.

Pesticide resistance management groups

Pesticides have been grouped according to how they work (site of action). Reduce the development of pesticide resistance by alternating pesticides from the different groups. The resistance management group is printed on the front panel of most pesticide labels, as shown in the example below. Canadian pesticide labels can be found on the PMRA website.