Thursday, 21 June 2018

Wheat midge (Jun 21, 2018; Wk 07)

Wheat Midge (Sitodiplosis mosellana– Recent dry conditions near Saskatoon have resulted in slower wheat midge development (compared to last week’s model output).  Predictions for 2018 (Fig. 1) are similar to long term average values (Fig. 2). 

Figure 1.  Predicted wheat midge phenology at Saskatoon SK.
Values are based on model simulations for April 1 – June 18, 2018.

Figure 2.  Predicted wheat midge phenology at Saskatoon SK.
Values are based on model simulations for Long Term Climate Normals.

When monitoring wheat fields, pay attention to the synchrony between flying midge and anthesis.  

In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. On warm (at least 15ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (photographed by AAFC-Beav-S. Dufton & A. Jorgensen below). Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.

REMEMBER that in-field counts of wheat midge per head remain the basis of economic threshold decision.  Also remember that the parasitoid, Macroglenes penetrans (photographed by AAFC-Beav-S. Dufton below), is actively searching for wheat midge at the same time.  Preserve this parasitoid whenever possible and remember your insecticide control options for wheat midge also kill these beneficial insects which help reduce midge populations.

Economic Thresholds for Wheat Midge:

a) To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage.

b) For yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled.

Inspect the developing kernels for the presence of larvae and the larval damage. 

The 2018 wheat midge forecast map was circulated in January and is posted below for reference.  Note that areas highlighted orange or red in the map below included surveyed fields with comparatively higher densities of wheat midge cocoons last fall.

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture or Alberta Agriculture & Forestry).  A review of wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011.  Additionally, more information can be found by accessing the pages from the new "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide".  View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.