When is the best time to trim Elm, Ash and Apple trees? Should they be sprayed for insects before or after trimming?
Arapahoe County Colorado trees and shrubs
Elm and ash trees should be trimmed March through about October. The optimal time would be in March before the trees have leafed out. Pruning when there are no leaves makes it easier to identify where to make the cuts.
For apple trees late March is the best time to prune. This would be before the bacteria that cause fireblight are active. Fireblight is a significant bacterial disease of apple trees along the Front Range and giving the pruning cuts sufficient time to "heal" before fireblight is active in the area would be a good preventative measure.
In terms of insect sprays, it is important to know what you would be spraying for. There are many insects that could potentially attack the three types of trees you mention and knowing what you are trying to prevent is important because both the timing and types of sprays vary.
If you have seen evidence of insects, would you know what they are or the symptoms your trees are showing? This would help us narrow down the treatments and I could make some suggestions for you. You can reply to this email if you have any further information to send.
Lastly, most insects don't attack healthy trees. Keeping your trees vigorously growing would be a great preventative measure that would go a long way to keep insects at bay. See the links below for suggestions on maintaining the health of your trees: