By Rebecca Hort, AAg, Extension Agrologist Intern, Regional Services, Yorkton
Grasshoppers are common insect pests of several Saskatchewan crops. They can cause damage and yield loss, so it is important to scout and control when necessary. However, not all grasshopper species are crop pests, there are 85 grasshopper species in Western Canada, with only four typically being pests to crops. It is important to know how to differentiate between pest and non-pest species.
Depending on your location and crop stage, scouting should begin when the crop is small; grasshoppers can cause damage early in the growing season. Producers should be watching for grasshopper populations beginning in June to quickly determine if action is required.
Scouting for grasshoppers can be difficult since they jump away as soon as someone walks into the field. There is a general way of scouting for grasshoppers that includes estimating amounts, or a more precise method.
When grasshoppers are seen evenly distributed throughout the field, this general scouting technique may be used:
- Walking into the field and determining an estimate of how many grasshoppers jump per square metre when you walk through. Be sure to scout multiple points in the field to gain a relative level of grasshopper population.
- Look for signs of feeding. If there’s crop damage from feeding, action may need to be taken.
Additionally, there’s a more precise method to scout for grasshopper populations:
- Measure and mark (or estimate) five 10 metre lines (50 metres in a line can be used if you are pressed for time but this won’t be as representative) on a flat road surface beside the field.
- Either in the field or in the roadside ditch, walk the 50 metres (total) disturbing the grass or crop once every metre and count the number of grasshoppers that jump up in a one-metre width.
- Once the total number of grasshoppers is collected from the 50 metres, divide it by 50 to get the average number of grasshoppers per square metre.
Grasshoppers usually move into the field and start feeding on the field edges. Therefore, it is best to start your scouting near the edge of the field. Use several random areas of the field to get an unbiased and accurate representation of the whole field.
Using a sweep net is very effective for identification. Four pendulous sweeps will give you a representative sample of nymphs per m2. This technique is much less effective for estimating adult or mature nymph numbers. Getting samples to determine the correct species of grasshopper will help you decide on potential control methods. Control for grasshoppers should be taken when they are in their third instar (the wings are present as short buds). This stage is easier to control since they are smaller, more susceptible to chemical control and not flying yet.
Below is the expected crop damage based on the amount of grasshoppers present.
- 0-2 per m² – None to very light damage
- 2 per m2 – Lentil pod and flax boll feeding economic threshold
- 2-4 per m² – Very light damage
- 4-8 per m² – Light damage
- 7-12 per m² – Action thresholds in cereals and canola
- 12-24 per m² – Severe damage
- >24 per m² – Very severe damage
For more information on scouting for grasshoppers, contact the Agriculture Knowledge Centre at 1-866-457-2377 or your local Ministry of Agriculture regional office.