Alfalfa weevil (June 13, 2019; Wk 10)

Alfalfa Weevil (Hypera postica) – 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 (AAW) across the prairies are updated weekly to help growers time their in-field scouting for second-instar larvae. 

This past week warmer temperatures in southern MB advanced alfalfa weevil development. Weevils are predicted to be primarily in the second (53%) and third instars (22%) across most of southern areas in MB and SK (Fig. 1).

Figure 1. Predicted average instar stage of alfalfa weevil (Hypera postica)  acrossthe Canadian prairies as of June 11, 2019.

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.  

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.