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Watch for Swede Midge in 2014

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

Swede midge caused some yield loss in northeast Saskatchewan in 2013, and caused heavy yield losses in the major Ontario canola growing region. Swede midge’s flexible biology could make it well adapted to the Prairies, like wheat midge is today.

Unfortunately, although there are insecticides registered for swede midge, there are no viable recommendations for control. There are no established economic thresholds or proven best timing for foliar sprays. So for 2014, the key message is to learn to identify swede midge damage so we can get a handle on the territory expansion of the pest.

Growers finding this insect should contact their provincial entomologist or CCC agronomist for additional information as it becomes available.

What to look for:

Swede midge females lay their eggs in canola apical meristems (growing points) — they’re after maximum nitrogen. 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. (See the photo above.)
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. (See the fourth photo above.) 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.

A small proportion of the swede midge population might overwinter in the soil for more than one season, emerge and migrate to nearby canola. Although swede midges are not strong fliers, they can be moved on wind currents. Unlike wheat midge adults, swede midge adults are active during the day, the same time as are pollinators.

Murray Hartman emphasizes the importance of early identification. Look for larvae inside florets, and for blackening and scarring of floret tissue typical of larval damage. Waiting until after flowering, when evidence of larvae is gone, can lead to some confusion as midge damage that creates the cluster effect to the growing point can look similar to Group 2 herbicide damage.

Source:  Alberta Canola Producers Commission


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