Would you please tell me the name of the disease on the spruce tree shown in the attached picture and how to treat it?
El Paso County Colorado trees and shrubs
This is cooley spruce gall.
- Cooley spruce galls are common and conspicuous on blue spruce. However, they do little or no harm to the tree.
- The galls are produced by aphid-like insects, Cooley spruce gall adelgids.
- Cooley spruce gall adelgids require two hosts to complete their normal life cycle: spruce and Douglas-fir.
- Once the galls begin to form, insecticides usually are ineffective because the insects are protected within the galls.
- The best times to spray are in the spring before new growth starts or in the fall when overwintering stages of the insect have returned to the tree.
Cooley spruce galls are commonly found on the new growth of spruce trees. These galls are produced by insects called Cooley spruce gall adelgids (woolly aphids). Galls appear early in the season as 2- to 4-inch cucumber-shaped growths. The galls are light green during late spring and early summer but dry out and become brown starting in mid-July. The galls often are mistaken for seed cones.
Cooley spruce galls are conspicuous and frequently cause considerable concern to homeowners. However, the galls usually do not cause any serious harm to the tree.
We don't recommend the application of insecticides for this problem, but you are free to do so if you would like. There is information on the following fact sheet on how to treat for this insect and what the most effective products are. If you have a large tree and/or you are not experienced with the application of insecticides, I would suggest contracting with a licensed arborist if you choose to treat the tree.
Let me know if you have any additional questions.