Last summer I visited several farms that reported having spruce trees with brown needles and the needles were falling off the trees.
This past week I received a call from one of those landowners who was following up from last year’s visit. Therefore, I thought I would talk about the culprit: the spruce spider mite.
When I made those farm visits last year, the spruce spider mites had already done their damage and left the landowner with little to do except hope the trees would not die. However, now is the time to scout for this tiny insect on needled trees, because there is something you could do now to prevent extensive permanent damage.
Spruce spider mites feed on needled evergreens and are most active during the spring. The damage appears as stippling, as the mites feed on chlorophyll in the leaves with their piercing mouthparts. Then in early to mid-summer the heavily attacked foliage will turn brown and needles begin to drop. Unlike a broad leaf tree, which will often grow new leaves after insects defoliate the tree, when the needles drop off the branch, new needles will not appear there.
This insect most commonly attacks spruce, but other species such as juniper, pine, Douglas fir, Frasier fir, and larch can be attacked as well. To scout for these tiny insects, vigorously shake the tree branch while holding a piece of white paper under the branch. Spider mites are so small that if they are shaken off on to the paper, there will be “moving dots” on the paper. Smash the dots, and those making greenish streaks are usually spruce spider mites that are feeding on the foliage; those making yellow-orange streaks are usually predaceous mites that are feeding on the spider mites.
If you notice the greenish streaks, and a lot of them without many of the predaceous mites, then it is time to take action. One approach on smaller trees is to spray the tree with a strong stream of water to knock them off the needles. The other option is to spray the tree with an insecticidal soap or a miticide.
When spraying the tree, concentrate the spray on the underside of the foliage, then repeat the application in five to seven days. If you had problems with spruce spider mites in the past, continue to scout for insects into early summer. Spruce spider mites will go dormant in the heat of the summer, but will become active again in the fall as air temperatures decrease, so scout again in the fall and take action as needed.
If you have questions about this insect, feel free to call me at the University of Illinois Extension office in Arthur at 217-543-3755.
For more information on University of Illinois Extension programming in Coles, Cumberland, Douglas, Moultrie and Shelby counties, visit our website at http://web.extension.illinois.edu/ccdms/index.html or call us at 217-345-7034.