Swede Midge

Swede Midge has been identified on a Meota area field, marking the first time it has been confirmed west of Prince Albert. Swede Midge started as a problem in Ontario in 2000, and with levels gradually building up over the years, led to the complete decimation of canola fields. Growers in Ontario blame Swede Midge as a key factor in their decision to switch to other crops. In Saskatchewan we haven’t seen the problem to that extent, with the first traps catching adult Midge in 2007 in Yorkton, Nipawin, and Melfort. Even with the adults being captured, it took until 2012 for damage from Midge to be observed, primarily in the Nipawin and Carrot River areas.

 

Life cycle

Swede Midge is an aggressive pest with the potential for more than three generations per year in Saskatchewan. In the spring, the adults emerge from cocoons in the soil. The males are alive for only one day during which time they mate, while the females are alive for up to four days; however, they’ll be relatively inactive if temperatures are below 20˚C. During these four days the females lay hundreds of eggs in the canola plant in clusters of 2-50 eggs. They typically prefer to be as near to the growth point as possible, but any actively growing vegetative tissue will suffice. The larvae hatch from these eggs within three days and then start actively feeding on the canola plant. The larvae live and feed for up to 21 days until they mature into pupae and drop to the soil surface to cocoon. The next generation usually emerges about two weeks later. If conditions are dry then cocoons will be deeper in the soil. Since moist conditions are preferred, in drier times the pupae will stay in cocoons in the soil for up to two years. Cocoons need high humidity but are typically found in the top centimetre of the soil.  In total this life cycle can take 21 to 44 days per generation, with the first generation usually emerging in late May – mid June, the 2nd in mid July to early August, and a 3rd generation from late August to early September. This multi-generation ability makes them different then their cousin, wheat midge, which has only one generation per year and can therefore be more effectively controlled with management and insecticide use.

 

Infection & symptoms

Only the larvae feed on the canola plant, but they are unselective with their appetite and will therefore eat whatever part of the plant they hatch on. This versatility also allows them to feast upon the various stages of crop development depending upon what stage the crop is when they they emerge.  In general, the younger the plant at the time of infection, the greater the degree of damage and yield loss that will occur, and if infestation occurs prior to bolting 100% yield loss is not uncommon. Conversely, if infection occurs after flowering is mostly completed, yield will not be affected.   The larvae damage the plant by breaking down plant cell walls and changing the physiology of the plant. Additionally, this damage makes the plant quite susceptible to secondary bacterial infections and rots typically set in particularly if weather conditions are moist.

 

Common damage symptoms are as follows:

  • Early infestation
    • Twisted or distorted young shoots
    • Swollen stalks
    • Stunted plant growth
    • Brown corky appearance to damaged tissue
    • Short side tillers
    • Lack of development of bolting racemes
  • Infestation at flowering
    • Misshapen buds, fused flowers, buds that remain closed, swollen flowers, or abnormal flower stem development
    • Stunted secondary branches
  • Infestation past flowering
    • Pods may be clustered
    • Branchy or broom like pod malformation.

 

The presence of Swede Midge can be detected through the use of pheromone traps which trap the adults that are flying into a field. As the larvae are extremely small, symptoms of damage are more observable than the larvae themselves.

 

Management

Both Coragen and Matador/Silencer are registered for the control of Swede Midge. However, Swede midge is not an ideal pest to eradicate with insecticide since there are multiple generations and since the larvae are usually inside the plant or flowers and pupae are in the soil. Spray timing is also an issue since adults are active during the day and effective spraying at this time would have a negative impact on pollinators and other beneficial insects. Control is therefore better managed through cultural methods such as crop rotation and a keeping a minimum distance of 1km from other canola fields. As early infestations can decimate the crop, late-seeding should be avoided. Heavier seeding rates can also be beneficial for reducing crop risk.

 

Swede Midge is considered to be fairly weak fliers and can be blown down wind. It will take awhile for populations to build up in a field and damage will typically be more concentrated around the field edges. If it’s a wet year Swede Midge will be more prevalent.

 

Once found on your farm it is unlikely Swede Midge will ever be eradicated. However, through the use of cultural controls you can reduce the likelihood of devastating crop loss.

 

References

Canola Council of Canada: “New Swede Midge Locations”

www.canolawatch.org/tag/insects-swedemidge/

 

Grain News: “Swede Midge: A potential ‘Perfect Storm’”

www.grainews.ca/2014/06/04/swedemidge-a-potential-perfect-storm/

 

OMAFRA: “The Swede Midge – A Pest of Crucifer Crops” www.omafra.gov.on.ca/english/crops/facts/08-007.htm

 

SaskCanola: “Assessing the Impact of Swede Midge on Canola”

  1. saskcanola.com/quadrant/…/report-Hallett-swedemidge-short.pdf

 

Saskatchewan Ministry of Agriculture: “Swede Midge: A New Pest in Canola”

www.agriculture.gov.sk.ca/agv1405-pg4

 

Real Agriculture: “Getting to Know Swede Midge”

http://www.realagriculture.com/2013/10/canola-school-getting-to-know-swede-midge/

 

The Western Producer: “Farmers Urged to Guard Against Swede Midge”

http://www.producer.com/2013/01/farmers-urged-to-guard-against-swede-midge/