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Scout for Spruce Sawfly (6/10/21)

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In previous years, yellowheaded spruce sawfly larvae have been observed at about 830 Growing Degree Days (base temp 40F).  With the recent very hot temperatures, that temperature threshold was met.  The larvae feed on first- and second-year needles of all spruce species and can be very destructive.  Sometimes whole needles are eaten; in other cases, the needles are damaged to the point where the ends dry out and turn a pink/brown color (see photos).  Most of the damage has been seen in central and western North Dakota.

Larvae feed for 30-40 days and are most susceptible to insecticides for the first two weeks of their development.  Carbaryl and acephate are both labeled for sawfly control.  For a small infestation, simply picking the larvae off the tree by hand and destroying them may be easier, and is equally effective.  A strong jet of water may also help reduced sawfly populations on trees.

When using insecticides, be sure to read, understand and follow all label directions.

Larvae of the yellowheaded spruce sawfly.  Notice that the tip of the needle in the lower right of the photo has been completely chewed off, reducing the needle to half its original length.  Photo taken near Minnewaukan, ND These needles were damaged by the yellowheaded spruce sawfly larvae.  The insects damaged these needles but did not consume them completely, resulting in brown/pink, dried-out needles.  Photo taken in Richardton, ND
Photo Credit:
Scott Knoke - 1 and Joe Zeleznik - 2(right)

 

Joe Zeleznik

NDSU Extension Forestry Specialist