European Elm Scale has become a bigger problem in Calgary in the last 6 or 7 years. Symptoms are not obvious unless the infestation level is high. Prevention is tough when untreated trees are nearby as the insects move fairly easily. As with most insects and disease, a healthy tree is less likely to be affected.
If you suspect your Elm has scale we recommend contacting a professional Arborist to discuss treatment options. Usually a combination of dormant season pruning and chemical controls applied by qualified professional is the best option. Elms in Calgary should only be pruned between October 1st and March 31st by law to prevent the spread of Dutch Elm Disease.