Introduction

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Additional Resources
Insect Control
For additional information on monitoring, economic thresholds and biological control of insects in field crops, as well
as information on insect management in commodities other than those covered in this guide, see the WCCP Guide to
Integrated Control of Insect Pests of Crops at http://www.westernforum.org/wccp%20guidelines.html.
Insect Management Decisions
Crop rotations, cultivar selections, and seeding dates can be chosen to reduce the risk of injury from some insects that
may be of higher risk to a crop. Management of insects with insecticides should only be considered when numbers or
damage exceed economic thresholds. To select an insecticide, verify the registered products for the insect and field crop
in the following tables. Consideration should then be given to the preharvest intervals, how the product will be applied,
restrictions, precautions and the hazard rating.
Preharvest Interval
The preharvest interval is the number of days that must pass between the last application of a pesticide and harvest.
Harvest is the cutting of the crop or removal of the produce from the plant. It includes direct-combining, cutting (swathing)
or grazing; it does not include swath-combining or baling for hay.
Field Scouting
Field scouting is the regular examination of fields to accurately assess the kind and the number of insects, plant pathogens
and weeds present and the amount of damage being done. Scouting should be done weekly during the growing
season and more frequently when infestations approach economic levels or when weather conditions favour the rapid
development of specific pests.
To properly scout for insect pests, you must know when they occur, where they live, what they look like, and how to find
and count them. The number of locations to assess in a field will depend on the field size, and any specific pests that may be
of concern. Generally a minimum of 5 sites should be sampled, however some insects may require more sites to be sampled
to accurately make management decisions.
There are several possible scouting patterns that can be used when checking fields.
These options are based on pest distribution and field configuration.
• Pattern 1: Used when pests are uniformly distributed.
º This scouting pattern typically looks like an X, Z or W, excluding field edges.
Pests that fit this pattern include aphids, bertha armyworm and diamondback
moth.
• Pattern 2: Used when pests are generally more
abundant at the edges of fields.
º Scout by walking along field edges, fence lines or
ditches. Some examples of when you would include
more focused scouting along field edges are to
estimate early-season populations of flea beetles,
Colorado potato beetles and grasshoppers.
In each area examined, use of a sweep net, if possible, is a good way to determine what potential pests and beneficial
insects may be present. This should be followed by examining some plants and the soil surface. More specific counts of a
particular type of insect or plant damage may be necessary if they are abundant during the more general scouting.
Economic Thresholds
Monitoring methods, typical symptoms, and economic thresholds or nominal thresholds for the more common crop pests
are described in the field scouting section for each commodity. The smallest number of insects (or level of injury) that
cause damage equal to the pest management costs is called the economic injury level. The economic threshold is the
density of insects (or level of injury) at which control measures should be applied to prevent an increasing population from