Pruning Wounds: Paint or No Paint?

By Phil Berwick
Living Tree Care

Once upon a time, when a branch was pruned off, the wound was covered with a ‘tree paint’. ‘Tree paints’ at that time were petroleum based and could inhibit callous growth formation from sealing over the wound.

A government research forester in the 70’s, Dr. Alex Shigo set out to show the detriments of tree paint. Using a handful of species, very thick tree paint was slathered over sensitive cambium tissue at the edge of the cuts, and his findings became gospel. This ‘finding’ has actually been more detrimental than beneficial to the urban forest. For to this day, with tree paint seldom if ever used, open wounds on certain species pruned during the growing season, attracts insects that can also spread disease.

Several of these insect vectors (carriers) have spores of vascular tree diseases on their bodies. So when a line clearance operation comes through an area, where for instance Oak Wilt is prevalent, trimming done during spring and summer leaves an oak vulnerable to becoming infected. This was also the plight of the American Elm. Whenever elms were trimmed during growing season months, they became ‘open season’ for Dutch elm disease.

Whenever possible, in our vicinity, especially oaks or elms, should be pruned during dormancy. But deadwood can be pruned off safely anytime, as long as the pruning cut does not venture past the branch ‘collar’ into live tissue. When that happens tree paint should be applied.

During the mid 70’s if we had descended from a tree, and missed painting a ‘shiner’, a pruning wound the size of a quarter, we had to ascend back up into the Elm and paint it. This was extreme, but realizing we were killing the American Elms by trimming them in the summer, we ceased spring and summer pruning. Now arboriculture has gone to another extreme by not painting wounds at all.

I have attempted to get utility companies to get their line trimming contractors to paint the wound of these certain hardwoods, or at least to not do line clearance trimming during the growing season on certain trees. It has been to no avail because it would slow down their pruning process.

Dr. Shigo had other findings regarding compartmentalizing of wounds in trees that were truly beneficial. I personally like to get my tree paint and other tree care health products at OK Hatchery in Kirkwood.

For more information contact Wendell Phillips Berwick, President/ Living Tree Care, livingtree@earthlink.net, 314-961-8733 (tree).