Second of two messages
I received two responses from extension staff, neither of which appear to match what I am seeing. The photgraph I provided was of excellent quality, so I am puzzled by the responses. Please see the attached photos. One is the photo I attached to my earlier inquiry. The other is a reference images from Utah State Horticultural department of European Elm Scale. It seems that I have a mild infestation of European Elm Scale. Thank you for your prompt responses.
We regret that you received a response with the incorrect name for the soft scale on your tree. Even so, congratulations on locating images which are a better match to the insects in your image.
As it turns out, both Calico Scale and European Elm Scale are uncommon pests of zelkova in Oregon. They are different species of soft scales that, when not managed, gradually weaken the infested tree(s).
Fortunately, management for both these soft scales is the same: Treat the scale as well as identify and, if possible, correct other adverse conditions. (Among the additive stresses to consider are a poor planting site; originally planted too deep; and circling roots.)
During recent years in the northwest, trees have been exposed to cumulative effects of higher than normal temperatures and less than normal rainfall. Even many of our native trees are failing. The bottom line is that stressed trees are easy victims of various pests.
Most landscape trees need supplemental deep irrigation (to about 8 inches) at least monthly during the dry months. Watering the surrounding lawn is not enough.
Management for European Elm Scale is as suggested in the publication you located:
- Manage trees to improve or maintain health.
- Monitor scale populations on host plants.
- Apply an insecticide (carbamate; horticultural oil; insecticidal soap; organophosphate; pyrethroid) to coincide with scale crawler activity. [The most environmentally sensitive of these are horticultural oil and insecticidal soap.]
- Apply a systemic neonicotinoid in spring after leaves have expanded. [Researchers urge caution with this group of pesticides because of the implications for damage to bees.]In addition, consider hiring a Certified Arborist for an onsite evaluation of the tree’s condition and treatment. Such persons must pass an exam and acquire continuing education. You can use your zipcode to search for a nearby Certified Arborist at http://www.treesaregood.org/findanarborist/arboristsearch.