Thursday, 31 January 2013 08:23

Small, but still increased risk of sawflies in southeast Alberta

Written by  Alberta Agriculture
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The area at risk of economically significant sawfly populations in 2013 will be limited to only a few areas. The 2012 field margin survey shows low populations in most of the area surveyed including the traditional sawfly areas in the Special Areas.


The damage ratings are based on 71 fields in 17 municipalities. One field was found with elevated but still low sawfly infestation in the M.D. of Acadia. The most significant populations are in Forty Mile County in southern Alberta.
Overall this is the lowest level of sawfly concern since the outbreak began over 13 years ago.
This continues the downward trend of sawfly populations that is the result of the use of solid stem wheat and naturally occurring parasitoids. Individual fields may still have higher wheat stem sawfly populations than indicated in the survey map.
The Wheat Stem Sawfly Map is based on cut stem counts conducted after the 2012 harvest. 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 little impact on sawfly populations and a high proportion of wheat stems cut in the fall will produce adults. Producers in areas with moderate to high levels of cutting should consider using solid stem wheat as a control strategy.
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. Feeding damage from the tunneling can result in hidden yield losses of 10 to 15 per cent. Further yield losses can occur from lodging at harvest. For more information about the life cycle can be found at wheat stem sawfly life cycle.
It is possible population hot spots still exist in areas of lower risk. Individual producers need to be aware of the potential risks in their own fields. Cutting levels higher than 10 to 15 per cent in the previous crop indicate the need to consider seeding solid stem wheat to reduce sawfly losses.
It is important farmers evaluate their individual situations in making their variety choices.
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.
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 in lower sawfly populations in Alberta.

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