Spruce Spider Mites Diagnostic Guide
Spruce spider mites, Oligonychus ununguis, are important pests of evergreens and present unique management challenges. This pest is most active in the cool spring and fall when it feeds on the needles of conifers causing a bronze or rust coloration to the needles, and potential leaf drop. Their populations build up quickly and by the time damage is visible in the summer, it may be too late for a treatment.
Trees at Risk
Colorado spruce, Norway spruce, white spruce, pine, arborvitae, cedars, Douglas fir, hemlock, junipers, and larch.
Colorado Blue Spruce
Signs of Damage
- Spider mites will first cause yellow spots on the needles.
- Heavy infestations can often cause a rust coloration.
- Damaged needles may drop prematurely, and twig and branch dieback may occur.
- Fine webbing can often be seen on needles.
- Spider mite adults (0.5mm oval shaped) can be seen with a hand lens.
- Shake a branch over a white piece of paper to see mites.
- Adults are dark green to black with salmon-colored legs and spines.
- Brown eggs are found in bud scales and at the base of needles.
- Eggs hatch in early spring and young mites begin feeding on old foliage. Spruce spider mites will not feed on the current year’s growth until after it hardens during the summer.
- Spruce spider mites are more active in the cool seasons of the spring and fall when the daytime temperatures are 60-700 F.
- Activity eases in summer with the arrival of 900 F weather and resumes with cooler weather in fall.
- When temperatures cool to 60-70 F during the day, feeding resumes and continues through late fall. Female adults lay eggs on the bark of small branches until a hard frost occurs.
- The eggs overwinter on the bark and needles.
- Several generations per year.
Spruce spider mites present unique management challenges. Populations build quickly and by the time damage is visible in the summer, it may be too late for a treatment. Monitoring is important for successful management of this pest. If a spruce spider mite problem was noted the previous fall, soil applications of Lepitect™ in the early spring are very successful.
Soil Application using Lepitect
Dosage: 0.2 - 0.4 oz/in DBH Timing: Treat at egg hatch (mid- April to early May). Otherwise, monitor and treat if populations begin to build in mid to late May. Re-Treatment: A second application 30 days later will provide additional control if larvae are still feeding.
Early spring Lepitect™ applications will provide excellent control of spruce spider mites. If mite populations are high, a second application may be required in late summer. Proper identification and treatment timing are important when managing mites. Using the prescribed miticides is very effective at controlling mites; using imidicloprid, however, can create mite flare-ups and should be avoided.
A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org