Wheat stem sawfly – Survey and maps

Results from recent and past pest survey work across Alberta.

Explore pages in:

This is not a forecast. It is a summary of the wheat stem sawfly situation in Alberta in fall 2023.


The wheat stem sawfly survey is an after-harvest survey completed in the fall of 2023. The population map is based on 87 fields in 20 municipalities across southern Alberta.

The continuing dry conditions of the 2023 growing season are aiding the growth of sawfly population in area, and in population. The cutting damage percentage in the areas known for sawfly increased, while cutting damage is being seen in areas where sawfly has not been an issue for many years.

Overall, sawfly is a real risk in 2024. The random nature of the survey means that individual fields may still have higher wheat stem sawfly populations than are indicated in the survey map. Producers are well aware of sawfly in their fields during harvest. Cutting levels of 10 to 15 per cent or higher in the previous crop year indicate the need to consider planting non-host broad-leaf crops or oats to reduce sawfly losses.


The wheat stem sawfly map is based on cut stem counts conducted in the fall after harvest. In each field, the number of stems cut by wheat stem sawfly and the number of uncut stems are counted in one meter of stubble in 4 locations along the headland. The percentage of cut stems is then determined by totalling the number cut stems and then uncut stems.

Survey findings

Field locations denoted by a black dot had zero sawfly found in the survey.

The percent of stems cut by sawfly gives an indication of the number of reproductive adult sawflies that will emerge in late June through early July. Winter conditions have very little impact on sawfly populations and a high proportion of wheat stems cut in the fall will produce adults.

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 and 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.

Find more information about the wheat stem sawfly life cycle

It is possible that population hot spots still exist in areas of lower risk, producers need to be aware of the potential risks in their own fields. Cutting levels of 10 to 15% or higher in the previous crop year indicate the need to consider planting non-host broad-leaf crops or oats to reduce sawfly losses. When populations are low it is typical to have small localized populations of sawfly that affect only one field or even just a portion of one field. At lower populations, wheat stem sawfly also tends to have a very strong edge effect where they migrate into the current year crop from the previous year stubble.

Parasitism can reduce populations and reduce the level of cutting. A parasitic wasp, Bracon cephi, has been shown to have significant impact on sawfly populations. The use of solid stem wheat varieties and the increase in parasitism are the major factors that lower sawfly populations in Alberta.


The 2023 wheat stem sawfly survey was carried out by the Alberta Agriculture and Irrigation, Plant and Bee Health Surveillance Section staff. Thank you Jon Williams, Agriculture and Agri-Food Canada, for building the map.

Population maps


Wheat stem sawfly – Overview

Economic thresholds for insects attacking cereals and corn

Back to Overview