Alfalfa weevil (May 31, 2018; Wk 04)

Alfalfa Weevil (Hypera postica) – The AAW model runs for Swift Current SK indicate that oviposition is well underway in southern Saskatchewan (Fig. 1).  Larvae should be primarily second and third instars. Fourth instar larvae may be occurring as well. 

Figure 1.  Predicted alfalfa weevil phenology at Swift Current SK. 
Values are based on model simulations (April 1-May 28, 2018 and projected to June 21, 2018).

Degree-day maps of base 9°C are produced using the Harcourt/North Dakota models (Soroka et al. 2015).  Models predicting the development of Alfalfa weevil (Hypera postica) across the prairies are updated weekly to help growers time their in-field scouting for second-instar larvae. Compare the following predicted development stages and degree-day values from Soroka (2015) to the map below (Fig. 2).  

Figure 2.  Predicted development of alfalfa weevil as of May 30, 2018.

The larval stage of this weevil feeds on alfalfa leaves in a manner that characterizes the pest as a “skeletonizer”.  The green larva featuring a dorsal, white line down the length of its body has a dark brown head capsule and will grow to 9mm long.  

Use the photo below as a visual reference to identify alfalfa weevil larvae.  Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.

Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon).  Additional information can be accessed by reviewing the Alfalfa Weevil Page extracted from the "Field crop and forage pests and their natural enemies in western Canada - Identification and management field guide" (Philip et al. 2015).  The guide is available in both a free English-enhanced or French-enhanced version.