Wednesday, 1 August 2018

Predicted grasshopper development (Aug 02, 2018; Wk 13)

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).  

Grasshopper populations were predicted to be in the adult stage (Fig. 1A). Development during this growing season is well ahead of average (Fig. 1B).  Development is predicted to be more advanced across the southern prairies than in the Peace River region. 

Figure 1.  Grasshopper development (percent of population) based on model output for the current
growing season (A) and for long term normal climate data (B).

This week, adults are predicted to be appearing across the Peace River region (Fig. 2C). 

Figure 2. Predicted grasshopper phenology at Saskatoon (A), Lethbridge (B), and Grande Prairie (C);
based on model output for the current growing season (April 1 – July 30, 2018).

Oviposition is ahead, and is predicted to occur across most of the southern prairies (Fig. 3).
Figure 3.  Predicted grasshopper phenology at Saskatoon (A), Lethbridge (B), and Grande Prairie (C);
based on model simulations for long term climate normals (April 1 – July 30).

Figure 4.  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 AgricultureSaskatchewan AgricultureAlberta 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.