Watch Your Spruce!

spruce defoliation

Defoliation by yellow-headed spruce sawfly larvae noticeably increased in central Minnesota last year and is predicted to buildup this year. This pest consumes the needles of white, blue, black and Norway spruce, and it its damage is most severe on open grown trees less than 10 feet in height. Eggs are inserted into slits sawed at the edges of new needles by female adult sawflies when new spruce shoots are expanding. This occurs about the time when lilacs are in full bloom.

The olive green and black striped larvae hatch in 7 to 14 days, are present from late May to late June, consume current year needles first, and then move back on the branch and eat older needles. Since this pest drops to the ground and overwinters in the duff below their defoliated spruce they can buildup and kill younger spruce by repeated defoliation over a few years. Control should center on visual inspection to locate the larvae, hand removal, or application of a labeled insecticide such as acephate, carbaryl, diazinon, or malathion.