Pest Management

Return to the Guide to Commercial Potato Production on the Canadian Prairies.

Apply only pesticides, which are registered for use in Canada and where there is a defined maximum residue limit (MRL) in the country of export. Countries, such as the United States, will not accept food with pesticide residues that are not approved by the Environmental Protection Agency. Consult with the potato processor or packer for a list of approved pesticides.

Pesticide Resistance Management

Selective breeding is an important tool in agriculture. Through selection of important traits, breeders have been able to produce the diversity of high yielding, high quality crops used in food production. Unfortunately, another form of selective breeding is detrimental. Through repeated application of pesticides, producers are inadvertently selecting resistant “breeds” of insects, weeds and diseases

How Resistance Developments

All natural populations have a wide variety of genetic traits. Within a population, there may be a few individuals that are naturally resistant to a particular pesticide. Pesticide resistance develops when a pest population is constantly being selected through repeated use of pesticides with a similar mode of action. The few surviving individuals multiply and eventually replace the susceptible population. The rate of increase of the resistant individuals within the population depends on the frequency of application and the reproductive potential of the pest in question.

Once resistance is established, pesticides within that chemical group are no longer effective. Weed resistance to herbicides is becoming more prevalent on the prairies and may affect weed management in potatoes. Populations of wild oats and green foxtail are known to be resistant to Group 1 herbicides (Poast Ultra, Select, Hoegrass 284). The Colorado potato beetle is notorious for its ability to have resistant populations selected, sometimes within two years after the introduction of a chemical with a new mode of action. Populations of the Colorado potato beetle in eastern Canada and most of the United States are resistant to many chemicals (Carbamates, Organophosphates, Organochlorines and Pyrethroids), forcing producers to rely on new chemical groups. Within the last several years, populations of the beetle resistant to most conventional insecticides have surfaced in Manitoba. To date, no insecticide resistance has been detected in Saskatchewan and Alberta.

The first signs of resistance are incomplete control of the pest after pesticide application. With weeds, this often appears as a healthy weed patch within a field where most weeds have been well controlled. However, before assuming resistance, other factors that could be responsible for pesticide failure must first be ruled out. Such factors include improper application (clogged nozzles, drift etc.), unfavorable weather (rain following application, wind, drought, etc.), and emergence of new pests (egg hatches, weed germination, etc.). If you suspect resistance, then you are strongly encouraged to contact your provincial potato extension officer.

Managing to prevent resistance to pesticides.

Prevention is the key strategy in resistance management. Once resistance has established, there is no “cure”. If available, alternative pesticides must be used. The development of pesticide resistance can be delayed by rotating between different groups (classes or families) of the pesticide, as each group tends to have a different mode of action. Pests or their offspring that survive an application would be killed by a pesticide from a different group in the following application. The rotation between pesticide groups could occur within the same or following season Pesticide resistance management through rotation of pesticide groups is only possible in situations where totally resistant populations are not yet present. Adequate record keeping of pesticide use is critical when rotating pesticides over years to minimize resistance development. Continued dependence on chemicals as the sole method of pest control is a sure recipe for the development of pesticide resistance. Agronomic practices can play an important role in managing pests and the development of pesticide resistance. For instance, a cereal crop planted after potato harvest to protect soil from erosion may also aid in controlling weeds. Crop residues shade weeds that require light to germinate and physically impede growth of young seedlings. Additionally, rye is known to contain allel chemicals that inhibit weed germination and growth. To manage Colorado potato beetle, plant the potato crop at least 650 feet (200 m) from last year’s crop. A significant number of beetles will over-winter in the previous field. The further the distance between the current potato crop and the source of over-wintering adults, the less chance the beetles will survive the journey to the new field. Refer to the sections on weed, insect and disease control below for more alternative pest control strategies that reduce dependence on chemical applications.

By implementing the following pesticide resistance management practices today, growers will ensure that there are more pesticides to choose from in the future.

1. Monitor your fields and apply pesticides only when necessary. Pest populations below an economic threshold can be beneficial, as they provide food for natural enemy populations and also serve to ensure genetic diversity within the population (i.e. they interbreed with resistant individuals, thereby diluting the resistance trait).
2. Employ agronomic practices that play a role in managing pest populations. For example, maintaining at least 650 feet (200 m) between the previous and present year’s potato fields will reduce the survival of over-wintering Colorado potato beetle adults.
3. Apply pesticides only to areas of the field where the pest is a problem.
4. Alternate between different groups of pesticides. Remember to take into account the pesticides you may wish to apply to control other pests later in the season. For example, if you expect to use an insecticide to control aphids later in the season, then choose an insecticide from a different family to control Colorado potato beetles early in the season. Alternate pesticide groups within and between years. Refer to your provincial crop protection manual for a listing of the different chemical groups.
5. Never repeat a treatment because adequate control was not obtained. This is the first sign that resistance is high. Always change chemical groups if repeated treatments are necessary.
6. Contact your provincial potato crop specialist if you suspect resistance is present. The sooner resistance is detected; the earlier alternatives can be implemented.