Predicted grasshopper development (Jul 26, 2018; Wk 12)

Grasshopper Simulation Model Output – The grasshopper simulation model will be used to monitor grasshopper development across the prairies. Weekly temperature data collected across the prairies is incorporated into the simulation model which calculates estimates of grasshopper development stages based on biological parameters for Melanoplus sanguinipes (Migratory grasshopper).  

As of July 23, 2018, most grasshopper populations are predicted to be primarily in the fifth instar or adult stages (Fig. 1A). Development is well ahead of average population development (Fig. 1B). Normally the first appearance of adults occurs during the last week of July (central Saskatchewan).  

Figure 1. Grasshopper development (average instar) based on model simulations for the current growing season (A) and
for long term normal climate (B) (April 1 – July 23, 2018).

Grasshopper development varied across the prairies, and was predicted to be more advanced across the southern prairies (e.g., Lethbridge; Fig. 2A) than in the Peace River region (fourth and fifth instar stages; Fig. 2). 

Figure 2. Predicted grasshopper phenology at Lethbridge and Grande Prairie.
Values are based on model simulations, for April 1 – July 23, 2018.

Figure 3.  Clearwinged grasshopper stages including egg, first to fifth instar stages and adult (left to right).

Grasshopper Scouting Steps: 

● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin.

● Starting at one end in either the field or the roadside and walk toward the other end of the 50 m making some disturbance with your feet to encourage any grasshoppers to jump. 

● Grasshoppers that jump/fly through the field of view within a one meter width in front of the observer are counted. 

● A meter stick can be carried as a visual tool to give perspective for a one meter width.  However, after a few stops one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance. 

● At the end point the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure. 

● Compare counts to the following damage levels associated with pest species of grasshoppers:

0-2  per m² - None to very light damage

2-4  per m² - Very light damage

4-8  per m² - Light damage

8-12 per m² - Action threshold in cereals and canola

12-24 per m² - Severe damage 

>24 per m² - Very severe damage

* For lentils at flowering and pod stages, >2 per m² will cause yield loss.

* For flax at boll stages, >2 per m² will cause yield loss.

Biological and monitoring information related to grasshoppers in field crops is posted by Manitoba Agriculture, Saskatchewan Agriculture, Alberta Agriculture and Forestry, the BC Ministry of Agriculture and the Prairie Pest Monitoring Network.  Also refer to the grasshopper pages within the new "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide" as an English-enhanced or French-enhanced version.