Swede midge: What to look for

July 16, 2014 - Issue 15

July 29, 2015 - Issue 19

Swede midge larvae feeding at the bud can stop stem elongation and leave pods in a cluster. Source: Owen Olfert

Swede midge larvae feeding at the bud can stop stem elongation and leave pods in a cluster. Source: Owen Olfert


Swede midge larvae inside floret. Source: Julie Soroka, AAFC

Swede midge larvae inside floret. Source: Julie Soroka, AAFC

Swede midge females lay their eggs in canola apical meristems (top growing points). Larvae hatching from those eggs feed within the meristems. Plant damage depends on the canola growth stage at which feeding occurs. The younger the canola plant, the greater the damage.

Damage typically includes one or more of the following:

—Distorted and twisted young shoots, and stunted growth if damage is very early.
—Misshapen individual buds in a bud cluster.
—Normal expansion of the primary raceme, but individual flowers are abnormal or only the flower stem and a small dried flower remnant remains.
—The primary raceme may be normal, but secondary branches may be stunted if infestation occurs later in flowering.
—Pods may form in a cluster because the growing point is damaged and stem elongation cannot occur. Sometimes secondary branches will look fine, and compensate to some extent.

At the rosette stage, the main growing point and secondary buds are contained within the apical meristem. If this meristem is severely damaged, dead tissue will have a brown corky appearance. These plants have little chance of recovery and if they do, will produce short side tillers with little pod set. This is the growth stage most susceptible to injury from swede midge.

If the primary apical meristem is damaged after bolting has started, the plant can develop strong side branches that can partially compensate for damage to the main raceme.

More detail on swede midge management.

Canola Watch