SPRUCE SPIDER MITES

Spider mites are a common pest of all spruce species in Alberta.  Adult insects may produce several generations per season, especially in hot and dry conditions.  While the adults are nearly impossible to see, they spin a fine webbing on the underside of the branches, which collects dirt and debris, and gives the needles a dirty, washed-out appearance.

Mites feed on the sap of needles, causing them to turn yellowish-green. Eventually, the needles turn brown and drop off the tree. The innermost branches are the most obviously affected, but spider mites will feed on needles to the tips of the branches.

Severe attacks are common during periods of drought, sometimes killing stressed trees.

During normal weather patterns, predator mites do a good job of controlling spider mites, and chemical sprays are not often warranted, except as a rescue measure on a badly infested tree.  In a hot and dry year, however, insecticidal spraying may be necessary to get high populations of insects under control.