1 - The pitch produced by a pine tree when it is injured is its own natural pruning sealer.

Yard and Garden March 11, 2017

Q.

The fierce winds we have experienced recently have broken several 3 inch branches on our pine trees. What shall I use to cover the breaks to prevent diseases from attacking the trees?

- A. A.

A.

I am sorry to hear that your trees were damaged, but I have good news for you. Pine trees can solve the problem themselves. Pines produce pitch (resin) to seal wounds and to reduce water loss from injuries. Pitch is a to a pine tree what a scab is for us, a protective covering of a wound. The pitch is not the sap of the tree because its primary purpose is not to carry nutrients within the tree, rather it is to close wounds and prevent the loss of sap.

If the branch broke away from the trunk and left a ragged wound, you should prune the stub closer to the trunk of the tree, leaving a clean (smooth) wound. The pitch will then close your pruning wound and you will not need to apply any wound sealer. Follow good pruning practices, leaving any branch collar, but not leaving a stub extending from the trunk. Please see Guide H-156: Tree Pruning Techniques.

If the branch broke in such a manner that it ripped the bark down the trunk some tree specialists may recommend only cleaning the wound to create a smooth edge to the wound. Others will recommend applying a wound dressing to the wound since it is larger because of the ripping of the bark. Once again, in the case of the pine tree the natural pitch should be sufficient to close even the ripped opening through the bark.

The pine trees, and other conifers that produce pitch, are able to care for themselves. It becomes more of a debate among tree professionals when the tree is not a conifer that produces pitch and when the wound is large and does not have the natural protection provided by the pitch. In the case of these trees, some will recommend using no wound dressing and some feel that some wound dressing substance is helpful. Remember that many commercial wound dressing materials have a petroleum base that can damage the young cells that the tree produces to naturally close the wound and actually inhibit wound closure. Wound dressing materials that are black or otherwise a dark color will absorb sunlight and become hot enough to inhibit natural wound closure as well. For these reasons, I think it best to use a water-based, light colored paint to use as a wound dressing if you feel that you must paint it. Latex paint will breathe and reduce the moisture in the wound area. Fungal spores will be deposited on the wound before you can apply a wound dressing, so creating a drier environment in the wound will help reduce diseases. A light colored paint will reflect heat rather than accumulating heat and will not inhibit wound closure.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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