Published: August 28, 2009 01:58 am      

Pine trees checking out for the summer

Around every corner of Oklahoma City there seems to be a pine tree that is completely dead or close to it. So what is responsible for all of these brown, crunchy trees? It can be narrowed down to two options in most cases. Unfortunately, the cure for both of the potential problems involves a chainsaw and a chipper.

The first potential problem is the weather. There have been several seasons of wet weather, leaving Oklahoma’s clay soil soggy and saturated. Pine trees do not prefer to have wet feet, meaning that they like for their roots to dry out occasionally. Having the soil saturated for an extended period of time could cause the tree an added amount of stress and lead to root loss.

Unfortunately, there is not much that can be done to alleviate stress brought on by weather conditions. It is important to consider what type of soil an area has when selecting a tree to plant. Sandy soils will drain more quickly than heavy clay soils. So you may want to look outside the pine family if your soils are of the clay type and you are planning to plant a new tree. This may save some heartache in the future.

The second problem that many pines are succumbing to is pine wilt. Pine wilt is caused primarily by a nematode. Nematodes are microscopic worm-like organisms. Nematodes that live in the soil may be more familiar, but this particular nematode makes its home inside the vascular system of the tree — the “pipes” that carry nutrients and water throughout the plant. You may remember back to biology class when you had to learn about the xylem and the phloem; these parts make up the tree’s vascular system. The nematodes are so happy once they are introduced into this environment that their population begins to grow exponentially and the vascular system is blocked. And there is no amount of Drano that will unclog these “pipes” and save the tree.

A pine infected with these nematodes will turn brown rather rapidly, usually during a two- to four-week period. But it may seem that the tree declines overnight if you don’t catch the death in process. I have heard many sad stories about a person going on vacation leaving a perfectly healthy pine tree behind and coming home to a dead-as-a-doornail tree.

There is no cure for this problem either. There is a preventative treatment that was studied by the University of Nebraska. This product, which is injected into the tree, was found to be only 63 percent effective, and there must be no chance that the tree has had any nematode pressure already. The treatments can be costly and are ongoing.

When examining a sample from a dying pine, it can be difficult to properly diagnose between these two lethal fates that the tree might be facing. There is a test that can be run by the diagnostics lab on the campus of Oklahoma State University. However, just because the sample comes back negative for the nematodes may not mean that there are no nematodes in the entire tree.

But you can rest assured that regardless if the problem is weather related or from the nematode, there is no magic spray that will turn the tree from brown to green. Pine trees rarely, if ever, pull out of a brown-ward spiral.

One thing that a concerned homeowner can do is to remove a dead pine, including the stump, as soon as possible.

The nematodes that cause the wilt are spread by an insect called a pine sawyer beetle. This is a boring beetle; not boring as in uninteresting, but boring as in it will chew out tunnels through the tree to raise a new “beetle family.” But this beetle cannot invade a live pine tree — the sap is too much of an issue. That is why it will look for a dead pine tree (one already infested with nematodes) to rear its young. The immature beetles will pick up a few of the nematodes and then go feed on a healthy pine tree, and that is how the saga continues from one tree to the next. Eliminating dead pine trees from the landscape will remove the “housing options” for the beetle and it should move onto browner pastures to make a home.



SAMANTHA SNYDER is an horticulture educator for the Oklahoma County OSU Cooperative Extension Service.