Elm trees are very fragile when it comes to pruning. Once an elm is pruned it is left helpless to prevent pests (such as elm bark beetles) and diseases (such as Dutch elm disease) from attacking and spreading into its delicate wood. Help your elm tree avoid pests and disease by using proper pruning techniques.
Elm trees attract a bug known as the elm bark beetle from mid-April through late-July. As a result, pruning an elm tree during these months is discouraged–and many states have ordinances against it. Elms should also never be pruned in the fall due to their susceptibility to fungi. The ideal time of year for pruning an elm tree is early spring. This allows the tree plenty of time to recover.
Avoid excessive injury to the tree by always cutting near the branch collar. The branch collar is located near where the branch is attached to the trunk or main limb. To cut off the branch, make a small undercut 1 inch away from the collar. Next, cleanly cut the branch from the top. Finally, cleanly cut the branch the rest of the way just outside of the branch collar. Never top cut an elm tree, as it can lead to scalding, infestations and lower property values.
If you must cut the branches during the summer or fall, wound care is vital for the overall protection of the tree. After removing the limb, paint the injury with a fungicide to avoid the tree contracting any fungus while the wound heals. Next, paint the tree with a mixture of half latex paint and half water to protect the injury of scalding. Finally, clear away any brush from under the tree to prevent wintering bugs from climbing the tree and damaging it.