The Master Gardener: Extra water can protect pines

Do you remember the bogeyman? I’m talking about the shadowy menace from childhood that lurked anywhere dark and scary. By investigating, we learned there was really nothing to fear; it was only scary because it was unknown.

There is a bogeyman in our landscapes. It has more substance than the childhood monster because it can actually kill trees, but almost as damaging is our ignorance and the decisions we make without knowing the facts. The bogeyman in this case is a group of wood-boring insects called pine bark beetles.

Bark beetles most often attack ponderosa pines in our area, but they can hit any pine. They tunnel under the bark and lay eggs. When the larvae hatch, they feed on the sap-conducting tissue of the tree while they mature. As adults they emerge, mate and fly to the same, or a different tree, where the process begins again.

When many beetles attack one tree, the larvae can eat so much that the sap stops moving and the tree starves to death. Repeated annual attacks can so weaken the tree that it dies, or succumbs to another pest. Bark beetles also carry the spores of a disease called blue stain fungus that plugs the vascular tissue over a period of years, and that too can kill the tree.

Bark beetles attack pines stressed by drought, fire, disease or mechanical damage. That means we can prevent attacks by keeping our pines healthy. Giving them extra water during drought periods can keep them beetle-free, or help them repel boring insects by literally pushing them out with pitch. Firewood often carries beetles with it, so don’t stack it next to live trees; do cover stacks with tarps to keep insects contained.

Unfortunately, there are some “urban loggers” out there who tell homeowners that their pines have bark beetles and need to be removed immediately. They might offer to do the job for a special price because they’re “already in the neighborhood.” If this happens to you, don’t assume that they are right; ask them to show you the evidence.

Evidence might include boring frass, which looks like discolored sawdust, on the ground or stuck in the bark. Pitch tubes, small patches of sap mixed with sawdust on the bark that are usually red or white, but not the normal amber color, might give a hint to infestation as well. Also, all the needles will turn yellow in one area of the tree, the top, middle or bottom depending on the species of beetle.

If you don’t see those signs, it is better to seek a second opinion from a certified arborist than to pay hundreds of dollars to remove a tree that may be just fine. Even if there are beetles, many homeowners are getting positive results with tree injections. This can be costly, but less expensive than removal. If you have questions, call the Master Gardener Plant Clinic or a certified arborist, but above all get more information before making any decisions. Don’t let the bogeyman win.