Thursday, 2 June 2016

Weekly Update (June 1, 2016; Wk 05) - Alfalfa weevil

Alfalfa Weevil (Hypera postica) – 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).

Degree-day maps of base 9°C are now being produced by Soroka, Olfert, and Giffen (2016) using the Harcourt/North Dakota models.  The aim or the modelling is to predict the development of Alfalfa weevil (Hypera postica) across the prairies and to help growers time their in-field scouting as second-instar larvae are predicted to occur.  Compare the following predicted development stages and degree-day values copied below (Soroka 2015) to the map below.

This week, alfalfa growers situated within ANY shade of purple should prioritize scouting for second instar larvae and compare it to the action threshold for alfalfa weevil which varies according to end use and crop stage.  

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