Issue: August 10th, 1998

Damaged bark on golden delicious apple

I live in Taos on the mesa. I planted a golden delicious apple tree last fall. This summer I have noticed serious damage to the bark like something is destroying it, but I have not seen an insect infestation. It is continuing to put out new growth, but I am concerned about the damage to the outer layer of bark.

I need to ask a few questions: (1) Do you see teeth marks in the bark to indicate that a larger animal, rabbit or such, is chewing? (2) Have you tried any insecticides? (3) On which side of the trunk (geographic direction - N, S, E, W) does the injury appear?

I ask these questions because they may help identify the problem. Without your answers, however, I will guess that the damage is on the south to southwest side of the trunk or the side that was to the south in the nursery before you planted them. Trees in New Mexico, especially newly planted trees and trees waiting in the nursery, are subject to a form of winter injury we call "southwest injury" because it occurs on the south to southwest side of the trunk. This injury develops because the bark exposed to the sunlight in the winter warms during the day, then freezes again each night. This alternate freezing and thawing kills the layer of tissue just under the bark. Then, as summer progresses, the bark begins to die and peel or flake off, so the symptoms may not appear until several months after the damage is done.

If no clear signs of animal or insect damage are present, I would suspect this southwest injury. The injured bark will be slow to repair, but in time new bark may grow over the injured area. To limit these problems, you might try painting the trunk of the tree with a cheap, water-based, white latex paint late next fall. This will reflect the heat during the day and reduce the temperature fluctuations.

I suggest that you also contact a local Extension Service person to take a look at the trees. Seeing them, they can do a better job of diagnosis. They also have resources, including me, to help them with the diagnosis.

Ash borers

There are little tan things sticking out from the bark of my ash tree. At first I thought they were little thorns, but when I touched them they were papery and hollow. There was a hole beneath them. What is this and should I worry?

You have described the pupal cases of either the ash and lilac borer or the clear wing borer. These are two moths that attack ash trees. The caterpillar stage of the moth is a borer, and what you see is the remainder of the "cocoon" which is left behind as the moth matures and leaves the tree to reproduce and cause more problems.

Should you be concerned? According to Dr. Mike English, NMSU Extension Entomologist, if the tree is healthy and you see less than one pupal case per foot, don't panic but begin to consider treatment. Now that the moths are emerging to reproduce is the time to apply a protective spray to the trunk and major branches of the tree if you observe three or more pupae per linear foot of trunk. Choose a product that is labeled for protecting ash or other shade trees from borers. The product will create a protective barrier that prevents the caterpillar from boring into the tree from its egg site in the crevices of the bark. Be sure to read and follow the label directions.

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.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!