Friday 24 May 2019

Alfalfa weevil (May 23, 2019; Wk 07)

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. 

Model output indicates that alfalfa weevil hatch has begun and first instar alfalfa weevils should be present across most of AB (Fig. 1). Model runs for Brooks AB (Fig. 2) and Swift Current SK (Fig. 3) were projected to June 15, 2019.  Second instar larvae will begin to occur late next week in fields near Brooks and 3-5 days later in the Swift Current region. 


Figure 1.  Predicted percent of grasshopper (Melanoplus sanguinipes) population at first instar stage across
the Canadian prairies (as of May 21, 2019). 


Figure 2. Projected predicted status of alfalfa weevil populations near Brooks AB to June 15, 2019,
using long term average temperatures.


Figure 3.  Projected predicted status of alfalfa weevil populations near Swift Current SK to June 15, 2019,
using long term average temperatures.

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.