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Spruce Sawfly Larvae Observed (06/27/19)

Yellow-headed spruce sawflies were seen this week in the Devils Lake area.

Yellow-headed spruce sawflies were seen this week in the Devils Lake area. They are primarily a pest of Colorado blue spruce, where the larvae feed on expanding needles. 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). This symptom can be subtle at first, but an experienced eye will pick up on it quickly. These insects prefer trees that are under (about) 20 feet in height. Spruce sawflies are usually found in the central and western parts of the state.

Over the last several years, the larvae have consistently been observed at about 830 Growing Degree Days (base temp 40°F). They feed for 30-40 days total and should be susceptible to insecticides for a least 2 more weeks. 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.

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Joe Zeleznik

NDSU Extension Forestry Specialist

 

Lezlee Johnson

North Dakota Forest Service

Forest Health Manager

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