Friday, August 11, 2017

Wheat Stem Sawfly Causing Problems in Polk County Wheat Fields

Prepared by Phillip Glogoza, Jochum Wiersma and Ian McRae

As wheat harvest moves northward, we are detecting infestations of Wheat Stem Sawfly in fields in Polk County. Recent storms and strong winds have helped bring these problems to front and center.
  
Farmers have noticed lodged stems, particularly on field margins, where in some cases plants are 100% lodged for 50+ feet from the edge inward. In those cases, the cut stems could be grabbed and picked up in a bundle (Figure 3) and the stubble below was all cut (Figure 4). As we  inspected the interior of these fields, the percent lodging, declined, but there was still evidence of Wheat Stem Sawfly damage.

Infestations have been found in the areas around Crookston and westward toward East Grand Forks. We urge farmers to pay attention to lodged areas of fields to determine if sawfly are a contributing cause of the problem. While driving the combine, lodged stems should be visible from the cab (Figures 1 and 2). 

Infested stems are plugged on the end by the larva for protection from the environment while overwintering (Figure 5). 

Cut stems, if sliced open, reveal the feeding damage and frass left behind by the sawfly larva (Figure 6).



These locations need to be noted so rotation and tillage can be performed to try and break the infestation cycle.


Figure 3. Wheat stem sawfly cut stems were so extensive, the cut stems could be picked up as a bundle on the edge of this wheat field west of Crookston, MN



    


The Following summaries are for the review of Wheat stem sawfly injury, biology, identification, and management: