Numbers of diamondback moths have increased in Western Canada over the past couple of weeks, in part due to the dry weather and strong winds. In some areas where the canola is still in late bloom, they are causing a fair amount of damage.
Héctor Cárcamo, entomologist with Agriculture and Agri-Food Canada, says the key to remember with diamondback moths is they usually aren’t a pest they’re feeding on the foliage.
“You can have a lot of holes on canola foliage and they will usually tolerate that level of damage. It’s when they finish feeding on the foliage, and they start feeding on the pods, that they really begin to effect your crop,” he explains in this Canola School episode.
The economic thresholds for diamondback moth larvae at this stage are nominal, which means they’re largely based on experience and not necessarily validated scientifically, says Cárcamo.
“When the larvae are feeding on the foliage and perhaps even some of the flowers there may be not any yield penalties. The problem is when there are no more leaves on the plants, and they start to feed on the pods. I think that is the key sign to be looking for when you are going to be making a decision about controlling them,” suggests Cárcamo. “Even if you have large numbers but you don’t see damage on the pods, then there’s probably not going to be an issue.”
To learn more about thresholds, damage, and why these insects are showing up, check out our latest Canola School episode: