2021 Southern Alberta Wheat sawfly map - credit Alberta Agriculture

By Dori Modney

Wheat stem sawfly poses real risk in Southern Alberta this year

Feb 17, 2022 | 3:38 PM

LETHBRIDGE, AB. — Increasing populations of wheat stem sawfly in various parts of Southern Alberta last year are expected to have a greater impact in the coming growing season.

The pests, and increased damage, were noted in a fall 2021 survey conducted by Alberta Agriculture, Farming Smarter and the Chinook Applied Research Association, particularly in counties that border the U.S,

Survey mapping was based on cut stem counts, in the fall after harvest, with damage ratings for 84 fields in 19 municipalities. Given the random nature of the survey, it’s possible individual fields could have higher wheat stem sawfly populations that indicated on the survey map.

2021 Southern Alberta Wheat Sawfly map – credit Alberta Agriculture

However, the map gives an indication of the number of reproductive adult sawflies that will emerge in late June and through early July, as winter conditions have minimal impact on populations.

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According to the survey report:

“Female sawflies lay eggs inside grass and grassy crop stems; the eggs hatch and tunnel inside stems until the crop starts to dry down near harvest. As the crop starts to ripen the sawfly larva migrates to the stem base a”nd cuts a notch most of the way through the stem, wind and/or wet weather cause the cut stems to break and the heads to fall to the ground. Feeding damage from the tunneling can result in hidden yield losses of 10 to 15% in each stem affected. Further yield losses can occur from lodging at harvest.”

Information provided by Alberta Agriculture, Farming Smarter and the Chinook Applied Research Association, producers need to be aware of risks to their fields, as sawfly population hot spots could still exist in areas of lower risk.

The survey report indicates that cutting levels greater than 10% to 15% in last year’s crop, indicates producers need to consider planting non-host broad-leaf crops or oats to reduce sawfly losses. When populations are low, sawfly can still have a very strong edge effect where they migrate into the current year crop from the previous year stubble.

As for reducing sawfly populations, a parasitic wasp, Bracon cephi, has been shown to have significant impact on sawfly populations. Using solid stem wheat varieties and increasing parasitism are the major factors to lowering sawfly populations in Alberta.

As the sawfly feeds not only on wheat but, rye, triticale and some varieties of barley, Alberta Agriculture has posted information on the insects’ life cycle, what to look for in a damage assessment and various management strategies on the Alberta Agriculture website.