Agriculture

Grasshoppers

Grasshopper

Grasshopper

Host Crops

Grasshoppers usually feed on forbs and grasses but, when abundant, they often will feed on vegetables and field crops, especially wheat, oats and barley. During severe outbreaks, grasshoppers tend to eat anything "green," including trees and shrubs.

Biology

Grasshoppers have one generation per year in Canada. Egg-laying usually begins in late July and continues into the fall. The egg pods are placed by the female in a cavity in the soil. Most grasshoppers overwinter as eggs in the soil. Egg hatch usually begins in late April or early May, peaks about mid-June, and is complete by late June. Hatching begins when the soil temperature has been 15ºC to 16ºC for about 200 hours.

Newly-hatched grasshoppers are about 5 mm (¼ inch) in length. These nymphs resemble the adults but have wing pads instead of wings and, therefore, cannot fly. There are usually five or six nymphal instars. Grasshopper nymphs mature in 35 to 55 days. The adults may live for four to six weeks after mating and egg-laying.

May June July August September
Egg hatching begins Feeding by nymphs starts Feeding continues, egg-laying begins Egg-laying continues, eggs begin overwintering Adults feed and die off, eggs overwinter

Scouting Techniques

Many agronomists use "foot-square" counts to rate their fields. This is simply the number of grasshopper nymphs that jump from a square foot area as you walk towards it.

To do a field survey, start at one corner of the field, walk diagonally past the centre of the field and then turn and walk straight out to one side of the field. Make at least 20 of these square foot counts in a survey. Dividing the total grasshoppers counted by two will give the approximate number of grasshoppers per square metre (sq. yd.).

Economic Thresholds

When populations exceed eight to 12 hoppers per square metre (sq. yd.), control is usually warranted. At the flowering and podding stage of lentils the threshold is 2/m2.

Control Tips

Early seeded, vigorous crops develop rapidly before the grasshopper eggs hatch. These crops can then tolerate feeding better than late seeded crops.

Hopper baits, containing an insecticide formulated on bran, are another option. Benefits include low cost, no harm to pollinators and most beneficial insects, and avoidance of insecticide drift. The bait can be spread by application equipment designed to spread granular herbicides or seeds, which is available from most agriculture retailers.

Insecticide applications are most effective and the costs are lower when they are applied after the eggs hatch and while the nymphs are still concentrated in their breeding areas.

Often, grasshopper nymphs can be sprayed in roadsides, headlands and field margins before they move into a field crop, vegetable garden or nursery. The lowest dosage given on the container label should be used when the grasshoppers are small and the vegetative cover is low.

Grasshoppers on rangelands may be effectively managed by applying certain insecticides in 30-metre swaths, alternating with 30-metre untreated swaths.

Less preferred crops, such as peas or oats, can be used as guard strips around more preferred crops.