Cultural Control of Grasshoppers in Annual Crops

Grasshoppers are a major pest of both cultivated crops and rangeland grasses in the world's semi-arid regions. Traditionally drier areas like southern Alberta and Saskatchewan are more prone to recurring problems, but serious grasshopper infestations can occur throughout the Prairies.

Although the majority of grasshopper damage has been to pastures and cereal grains, other crops can be seriously affected. In a more diversified agricultural landscape where cereal crops are often rotated with other cultivars such as canola, lentil and peas, grasshoppers continue to cause significant economic loss. The type and extent of crop damage will depend on the type of crop, how well the crop is growing, the number of grasshoppers present, the species of grasshopper, and whether or not adequate cultural and chemical controls are used.

Of all the methods available for grasshopper control, cultural control methods are generally the least expensive. These methods involve good management strategies and the proper timing of normal operations necessary in the production of a crop. The principal cultural methods used to control grasshoppers include early seeding of crops, crop rotation, tillage and trap strips. Cultural control is a preventative approach, and will not eliminate grasshoppers.

Crops should be seeded as early as possible. Older plants that are growing vigorously can withstand more grasshopper feeding than younger plants, which are not well established. Although early seeding will not prevent crop damage entirely, it will reduce the amount of damage to crops and allow more time for the producer to obtain and apply insecticides. Early-seeded crops also mature early, and migrating grasshoppers are less likely to be attracted to them as they are to lush, young foliage.

Whenever possible, avoid seeding cereals on stubble fields heavily infested with grasshoppers. Seeding cereals on stubble fields that had large numbers of grasshoppers the previous August could also be trouble, as they may have laid eggs there. Cereals should be seeded on stubble fields only where soil moisture is adequate and where one or more applications of an insecticide over the entire field is economical.

Cultivation of the soil is a cultural practice available to producers for the reduction of grasshopper populations. Tillage controls grasshoppers primarily by eliminating the green plants on which they feed. Tillage can also be used as an emergency measure on small areas where there are suspected large numbers of eggs. The tactic is to bury the eggs and hatching grasshoppers deep enough so that the young hoppers cannot make it to the surface. The practice is of little to moderate value if used for the sole purpose of physically destroying grasshopper eggs or exposing them to desiccation, or predation by birds and other predators. Excessive tillage will reduce soil moisture levels and increase the risk of soil erosion, factors which should be considered carefully under drought conditions. Tillage is primarily recommended as a last resort in fields to control hot spots, and is most effective used in combination with trap strips.

It is advisable to complete early spring weed control to eliminate all green growth on stubble fields before the grasshoppers have hatched. If no food is available for the young grasshoppers to eat when they hatch, they will starve. Early weed control also provides additional benefits; it gives good weed control and conserves moisture at minimal cost. Control of weeds in the late summer and fall may reduce the number of eggs that adult female grasshoppers lay at the site.

Trap strips can be used to protect fields which had low to moderate infestations in the previous year, and where little green growth was present on the field either in the spring or fall prior to seeding. To make trap strips, cultivate a black guard strip 10 m wide around the outside of a field. Leave an unworked green strip of at least 10 m before resuming cultivation. Repeat the process as often as necessary to produce additional trap sites. All green vegetation must be eliminated between the trap strips. The black guard strip is enough to ensure that grasshoppers will move promptly into the trap strips to feed. However, this trap strip does not have enough vegetation to feed a large grasshopper population for more than one or two days.

Trap strip effectiveness can be improved considerably by seeding the strips to wheat, spring rye, or barley several weeks before seeding of the main crop begins. The migration of young grasshoppers from the cultivated guard strips to the trap strips may take several days. Once the migration is complete, the trap strips and a 10 m strip of any adjacent crop should be treated with an insecticide. The highest application rate recommended for the insecticide used should be applied to ensure adequate control is achieved.

Be sure to assess the effectiveness of the insecticide. If adequate control is not achieved, it may be necessary to treat the trap strip again. When grasshoppers have been eliminated from the trap strip, it should be possible to remove the trap strip without fear of displacing large numbers of grasshoppers into the adjacent crops.