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Grasshoppers: forecast, monitoring and management

2022 grasshopper forecast

Each year, Manitoba Agriculture forecasts the potential risk of grasshoppers to field crops. This forecast is based on counts of grasshopper populations in August 2021 conducted by entomologists, agronomists and extension specialists. It also incorporates weather data, recent trends in grasshopper populations and the presence of natural enemies. The forecast is intended to estimate the risk of pest grasshoppers, allowing farmers to adapt their management and monitoring practices.

The survey showed light to moderate grasshopper populations across much of Manitoba, with a small number of counts in the central region indicating severe or very severe risk for 2022 (Figure 1). Grasshopper populations have steadily increased over the past few years, with favourable conditions during the 2021 egg-laying period. Farmers should scout along roadsides and field edges to catch young grasshoppers early in the season.

The complete Manitoba Grasshopper Forecast for 2022 is available here.

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Figure 1: Average density of grasshoppers in Manitoba in August 2021.

Large amounts of moisture this spring may have farmers wondering about the survival of grasshopper populations. In Manitoba, all pest species of grasshoppers overwinter in the egg stage, which is very tolerant to flooding. For this reason, spring flooding will have had little impact on grasshopper survival.

Once grasshoppers hatch, persistently cool, wet weather can reduce populations by slowing their development and increasing their susceptibility to predators and pathogens.

Identification and crop preferences

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Figure 2: Two-striped grasshopper nymph.

Of the 85 species of grasshoppers in Manitoba, only four are potential pests of crops. The potential pest species are the migratory, two-striped, clear-winged and Packard grasshoppers.

  • Migratory grasshoppers feed on both grasses and broadleaf crops. Preferred crops include both wheat and barley.
  • Two-striped grasshoppers feed on both grasses and broadleaf crops. They prefer heavier-textured soils and are one of the earliest pest species to hatch.
  • Clear-winged grasshoppers feed primarily on cereal crops, rarely on broadleaf crops.
  • Packard grasshoppers will feed on both broadleaf plants and grasses. They prefer light-textured soils.

Any grasshopper that is flying prior to June is not a pest species. Grasshoppers with red, yellow, orange or black wings when flying are not pests, and any grasshoppers that make noise are not pests, as pest species are silent. For details on identifying pest species of grasshoppers, reference this factsheet from Manitoba Agriculture.

Scouting

Early season scouting is important to monitor and control pest species of grasshoppers, as this helps farmers to catch problems before damage is too great and manage populations at the more susceptible nymph stage of their life cycle. Farmers should begin scouting in late May to early June. Cool conditions this spring may slightly delay grasshopper hatching to early or mid-June.

There are several ways to scout for grasshoppers or estimate damage:

  • Metre square count: Count (or estimate) the number of grasshoppers that jump from a one-metre-square area as you walk towards it. Once you reach the area, disturb the plants with your feet to count any remaining grasshoppers Repeat at least five times, but do not continue to walk in a straight line to prevent overestimating populations. Note areas with higher populations, such as field margins or wet areas during droughts.
  • Sweep net sampling: Sweep net sampling should not be used to assess population levels, but it can be useful for determining the species and stage of grasshopper populations to optimize management.

Management

Management through use of insecticides can be useful and effective. However, a variety of other practices can be implemented to manage pest grasshoppers or mitigate risk:

  • Crop choice: Crops that can be planted early and grow rapidly before grasshoppers hatch will better withstand grasshopper feeding. Peas and oats are less preferred by grasshoppers and may be used as guard strips around crops of concern.
  • Seeding date: Plant crops as early as possible, as older plants better withstand grasshopper feeding.
  • Preservation of natural enemies: Many predators and parasitoids of grasshoppers exist. By minimizing the use of broad-spectrum insecticides when not needed, the populations of natural enemies will be maintained to keep grasshopper populations in check. For more information on the natural enemies of grasshoppers, reference the Pests and Predator’s Field Guide from Field Heroes.

When populations of grasshoppers exceed 12 per square metre, control by insecticides may be required. Young grasshoppers are much easier to control than older populations and are usually concentrated around field edges. In many cases, treating only the field margins with an insecticide is sufficient.

Table 1: Grasshopper economic thresholds as recommended by Manitoba Agriculture and the Prairie Pest Monitoring Network.


Additional Resources

Manitoba Agriculture

Grasshoppers: Identification, Monitoring and Management

Agriculture and Agri-Food Canada

Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management

Grasshopper Identification and Control Methods to Protect Crops and the Environment

Western Committee on Crop Pests: Guidelines for the Control of Insect Pests

Cereal Grains – wheat, barley, corn

Oilseeds – flax, sunflower

Prairie Pest Monitoring Network

Weekly Update Week 2 2022 – Predicted Grasshopper Development

Grasshopper Diversity and Scouting Photos

Grasshopper Lifecycle, Damage, and Scouting and Economic Thresholds