Grasshoppers and the Jump to Canola

Earlier this season, reports of Diamondback moth were coming in and the amount of damage they were causing was alarming. (Figure 1.). After checking fields for this pest, yet another pest problem has emerged!

Grasshoppers have moved in from nearby maturing wheat fields and shrub-steppe and are amassing in large numbers, especially in canola fields that are still green, as some still are in Douglas County, WA. According to the Canola Council of Canada, the action threshold for grasshoppers is 8 to 12 per square meter. There were 27 grasshoppers on the hood and windshield of my vehicle (roughly 1 square meter) with adults jumping and flying all around (Figure 2).

The grasshopper species present were the Twostriped, (Melanoplus bivittatus (Say)), and migratory, Melanoplus sanguinipes (Fabricius), both common species in the western U.S.

Grasshoppers are generalist feeders and will attack an array of plants. They may become more abundant in years when conditions are hot and dry.  A reduction in natural vegetation can oftentimes make cultivated crops, such as canola, more appealing. Both nymphs and adults can cause significant feeding damage, especially when feeding occurs on the developing or ripening pods.

Monitoring and getting an accurate count of grasshoppers can be difficult as they are prone to jumping and flying when disturbed. Therefore, the Canola Council of Canada has developed the following monitoring protocol taken from the Prairie Pest Monitoring Network.

1. Measure off 50 meters (164 feet) on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin.
2. Starting at one end, either in the field or the roadside, walk toward the other end of the 50 meters, making some disturbance with your feet to encourage any grasshoppers to jump.
3. Grasshoppers that jump/fly through the field of view within a one-meter (3.28 feet) 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.)
4. At the endpoint, the total number of grasshoppers is divided by 50 to give an average per square meter.
5. 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

Grasshoppers will likely be most abundant along field borders and it is recommended to try and treat them when they are 3^rd or 4^th instars (yet to have mature wings) and thus are not flying from field to field. If an insecticide application is warranted, products containing BIFENTHRIN (such as Discipline 2ec), CHLORANTRANILIPROLE (such as Coragen Insect Control), CYANTRANILIPROLE (such as Exirel Insect Control), DELTAMETHRIN (such as Delta Gold 1.5EC), LAMBDA-CYHALOTHRIN (such as Lamdastar) and ZETA-CYPERMETHRIN (such as Mustang Maxx) are all registered for canola. For a complete list consult the PNW Insect Management Guide or  Pesticide Information Center OnLine (PICOL) Database.

Note: ALWAYS CONSULT THE INSECTICIDE LABEL BEFORE APPLYING ANY INSECTICIDE.

When spraying insecticides, always be mindful of pollinators and other beneficial insects. (See I Need to Spray for Insect Pests, But I Am Concerned About All the Bees) For additional insect management information, visit the WSU Wheat & Small Grains Insect Resources webpage.