While most canola producers in western Canada are still keeping an eye out for wireworms and cutworms, there are more reasons to scout on the horizon. Those reasons? Cabbage seedpod weevils and lygus bugs.
For each species, there are a series of factors that might influence the susceptibility of a given canola crop to infestation. For example, canola adjacent to alfalfa might see greater numbers of lygus bugs, while fields that saw high fall populations of adult cabbage seedpod weevil are likely to see them again. Seeding date also plays a role.
The Role of Seeding Dates
“We notice a very interesting pattern with regards to seeding date on seedpod weevils and lygus bugs,” says Hector Carcamo, entomologist with Agriculture and Agri-Food Canada. “If farmers plant their canola early…cabbage seedpod weevils tend to accumulate in those fields and quite likely that they’ll surpass the economic threshold.”
For lygus bugs, Carcamo says the opposite pattern is true, with early seeded fields likely to see reduced risk.
When to Start Scouting
Producers should begin scouting for cabbage seedpod weevils from the bud stage through flowering. Once the crop is roughly 90% in flower, it’s time to keep an eye out for lygus bugs as well.
— Shelley Barkley (@Megarhyssa) June 8, 2016
Tips for Scouting Lygus Bugs
When scouting for lygus bugs, Carcamo suggests:
- Taking sweeps in areas that are representative of the stand. Unlike scouting for cabbage seedpod weevil, it’s okay to sample along the edges of fields.
- Making sure you’re not counting aphids in your net. It’s pretty easy to get the two mixed up, but think of lygus bug nymphs as “runners” and aphids as “joggers.” And if you see a cornicle (or, “tail pipe”), you’re looking at an aphid.
- Only counting the lygus that are big enough to damage the crop. “You actually can see these wing pads that are beginning to form, and if you are not able to see those shoulder pads or wing pads, then you should not be including it in the threshold count.”
- Remembering that there is an “army of natural enemies” to consider when making that decision on whether or not to implement control strategies.
According to Carcamo, thresholds for lygus bugs are relatively specific to regions, and work is being done to determine thresholds for higher rainfall areas. In many of these regions, the crop may be able to tolerate lygus bug populations that exceed the thresholds used today.