Grasshoppers are a major pest of both cultivated crops and rangeland grasses in the worlds' semi-arid regions. Traditionally drier areas like southern Alberta 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 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.
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 will allow more time for the producer to obtain and apply insecticides. Also, early-seeded crops mature early, and migrating grasshoppers are less likely to be attracted to them as they are to lush young foliage.
Whenever possible, avoid seeding cereal on stubble fields heavily infested with grasshoppers. 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. Using tillage to control grasshoppers has to be considered carefully, especially under drought conditions. Tillage controls grasshoppers primarily by eliminating the green plants on which grasshoppers feed. The practice is of little value if used for the sole purpose of physically destroying grasshopper eggs or exposing them to desiccation, predation birds and other predators. Excessive tillage is harmful in that it will reduce soil moisture levels and increase the risk of soil erosion.
Fall tillage to get rid of weeds from summerfallow during late summer and early fall will discourage female grasshoppers from depositing their eggs in these fields. Grasshoppers seldom lay eggs in clean summerfallow even when it has a heavy covering of trash. Similarly, thorough field cultivation immediately after harvest will help discourage grasshoppers from laying all their eggs in the field.
It is advisable to complete early spring tillage or chemical fallow 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 tillage also provides additional benefits: it gives good weed control and conserves moisture at no extra cost.
Tillage can be used as a last resort in fields where there are defined "hot spots," that is, where the young grasshoppers are continuing to hatch in large numbers and continued chemical applications are not desirable. In this situation, the tactic is to bury the eggs and hatching grasshoppers deep enough so that the young hoppers cannot make it to the surface.
If grasshoppers are present when tillage operations begin, it is probably possible to achieve adequate control by simply eliminating all green plant materials in a field. Once grasshoppers have fed and developed to the second stage of growth (second instar) in a field, they are usually mobile enough to move to adjacent crops when their existing food supply is exhausted, In these fields, trap strips should be used to collect grasshoppers into a relatively small area where it will be possible to control the insects quickly and economically.
To make trap strips, cultivate a black guard strip 10 metres wide around the outside of a field. Leave an unworked green strip of at least 10 metres 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 or spring rye several weeks before tillage 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 metre 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.
Before cultivating the trap strips, wait three days 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 complete tillage without fear of displacing large numbers of grasshoppers into the adjacent crops.