JoAnne Skelly: Prune evergreen trees in late fall
September 25, 2017
With more than 100 trees on our property, there's always pruning to be done. I've been waiting all year to do much-needed pruning or tree removal on our pines and spruces. I had meant to prune last year in late fall, but never was able to get to it. Winter brought all the flooding and prevented me from pruning then. Now, I'm waiting for a couple of hard freezes so I can clean up, limb up or cut down various evergreen trees.
While many publications across the country promote pruning evergreen trees during active growing seasons, why do I say wait until late fall or winter? Bark and wood-boring beetles are why. These are common tree-killing pests throughout Nevada and the West and are active in spring and summer. Since pruning is controlled wounding of a tree, pruning evergreens during those seasons sends out signals (chemical pheromones) the trees are in distress. The beetles then attack, laying eggs in bark crevices. When the larvae hatch, they bore through the bark into the live wood of the tree and feed, which interferes with water and nutrients flow up and down the tree. This weakens the tree and eventually may kill it. Beetles are rarely active after a few good freezes, so it's much safer to prune evergreens in late fall or early winter.
Evergreen trees usually need little pruning, so why prune at all? Some of our trees are almost 50 years old. There are a lot of dead branches that need to be removed. In some cases, tree limbs are blocking the driveway or the reach of the sprinklers. There are a couple of trees I want to remove altogether, because they were planted too close together all those years ago. By eliminating those that abut each other, I can give the remaining tree a better chance to thrive. In some areas of the yard, I want to remove the lower limbs of the tree to open up views or to make mowing easier.
Good sharp saws and loppers are a must for clean pruning cuts. To avoid potential spread of diseases, I disinfect my pruning tools with rubbing alcohol between trees. I never paint cuts because it doesn't do the tree any good and can actually harm a tree. Be safe; hire a certified arborist for big jobs.
Here is a link to a good pruning guide: https://pubs.ext.vt.edu/ 430/430-455/430-455.html.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.