Overview

The sawfly survey conducted in fall 2021 clearly shows an increasing population in various parts of southern Alberta. Increased levels of sawfly damage was found in those counties bordering the 49 parallel. Damage was less severe as surveyors move west from the Saskatchewan border but never the less cutting was found across this region. The drought conditions of 2021 contributed to the population success of this insect.

Methodology

The wheat stem sawfly map is based on cut stem counts conducted in the fall after harvest of 2021 and the damage ratings are based on 84 fields in 19 municipalities. In each field, the number of wheat stem sawfly cut and the number of uncut stems are determined in a one meter of stubble in four locations.

Survey findings

Overall, the sawfly is a real risk in 2022. 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.

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 higher than 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.

Acknowledgements

The 2021 wheat stem sawfly survey was carried out by the Alberta Agriculture, Forestry and Rural Economic Development with support from Farming Smarter and Chinook Applied Research Association – thank you for your contribution. Thank you David Giffen, Agriculture and Agri-Food Canada, for building the map.

Historical population maps

Resources

Wheat stem sawfly - Overview

Economic thresholds for insects attacking cereals and corn

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