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The Importance of Resistance Management by Paul Pilon

September 28, 2010

Growers commonly use pesticides to control various insect and disease organisms that commonly attack or feed on their crops. Chemical pesticides are divided into various classes depending on the type of pest they are effective at controlling. For example, fungicides are used to control plant pathogens, insecticides are used to control insect pests, and miticides are effective at controlling various types of mites. Unfortunately, many pests are capable of developing resistance to many of the pesticides growers use to control them.

Pesticides are usually most effective at controlling a pest when it is applied to a particular life cycle, or stage of development, of an insect or disease. The application of these products to non-responsive life stages results in less overall control of the targeted pest or disease. The greatest level of control is obtained when growers pick pesticides which are appropriate for controlling the desired pest, and apply them to the life stages which will yield the greatest results. 

The method pesticides control or act against the living systems of the pest is called the mode of action. Each pesticide is classified by its mode of action and products that share a common mode of action belong to the same chemical class (sometimes referred to as chemical family). Once a pest develops resistance to a specific pesticide, it is usually resistant to all of the products within that chemical class.

Overtime, growers should not rely on a single pesticide to control a particular pest or disease. Understanding which chemical class, or family, each product is from will help growers to pick alternate chemicals which have different modes of action, belong to different chemical classes, and have a greater likelihood of providing an improved level of control of the targeted pest.

Today’s growers need to be concerned about pests building up resistance to the chemicals being applied to control them. Pest biology, the intensity of past and present pesticide applications, and commercial production practices, are all contributing factors leading to resistant insect and disease organisms. 

The first step to reducing potential pest resistance is to reduce the reliance on synthetic pesticides. When and where possible, growers should try to use non-chemical methods of controlling pests such as implementing cultural, mechanical, physical and biological management options.

For managing resistance, the best chemicals are those that work quickly after application, and quickly disappear from the crop area, reducing the length of time pests are exposed to these products. Pesticides that are long lasting, or degrade slowly over time, often only kill the most susceptible portion of the pest population and leave behind the resistant pests, which reproduce and produce an even more resistant pest population.

Growers use several approaches to determine when to rotate the pesticides being applied. Long term rotations consist of using one product throughout at least the duration of one pest generation before rotating. With overlapping pest populations containing all life stages present, many growers use the same pesticide for a least two generations prior to rotating.  Other growers practice rotating chemicals with each application. When rotating pesticides, it is important to rotate to chemicals found in different chemical classes, or having different modes of action then the one previously applied.

Considering the potential of pest populations to build resistance to pesticides is an important aspect of controlling insects and diseases. Growers should follow good plant health and sanitation practices, use effective pesticides at their labeled rates, apply pest control products to the appropriate life stages they effectively control, rotate between products with differing modes of action, only apply these products when necessary, and minimize the number of applications being applied to each crop. 

Failure to practice good resistance management strategies will result in inadequate levels of control, increased use of pesticides and cost, and may adversely affect the value and marketability of the crops being produced.

Additional information regarding resistance management and tables containing pesticide mode of actions can be obtained from the following websites. For insecticide resistance and mode of action: www.irac-online.org and for fungicide resistance and mode of action: www.frac.info/frac/index.htm.

Paul Pilon
Perennial Solutions Consulting
paul@perennial-solutions.com

 

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