Is it pine wilt? |

Is it pine wilt?

Richard Snell
Barton County Extension Agent

The recent drought and heat has been extremely tough on our trees. I have already noticed that many evergreens, including spruce and arborvitae, have succumbed to the dry conditions. I have also seen some pines beginning to turn color and die. The question is, are these pines dying from pine wilt or the drought?

Put a good article in the paper about a particular problem and suddenly everyone thinks they have it. Such is the case with pine wilt. Now everyone thinks their cedar, blue spruce or arborvitae has it. First, only pine trees get pine wilt, none of the others.

Some of the pine mortality this year, especially those of white and Austrian pines, has erroneously been blamed on the pinewood nematode. We rarely detect the nematode in pine species other than Scots or Scotch (same tree) pine, and even when we do find it in let’s say an Austrian pine, it is debatable whether it was the primary cause of the disease.

Certainly, pine wilt has been epidemic on Scots pine the last several years and has resulted in extensive mortality of this species in the eastern half of the state. The past five years we have become increasingly aware of it as we have lost a number of trees to pine wilt in Barton County. Most have been out in the country where there are windbreaks or multiple pine plantings.

There could be several explanations, including the fact that the nematode is not uniformly distributed in a dead tree and that we are missing it in sampling. However, I believe that some of these pines are simply dying because of drought.

Another possible and likely cause is diplodia tip blight or other needle disease. This disease has been around for years and has killed trees after they have had it for several consecutive years. This develops into Sphaeropsis canker and branch die-back.

In most cases, trees aren’t dead but do have needle scorch from the heat or just some browning from the tip blight disease. Assuming that branch die-back has not occurred yet, you can spray for tip blight in the spring with a fungicide.

In the end, it is probably a moot point whether the pine died of drought or the pine wilt. In both cases the tree should be removed as quickly as possible after October 1 to prevent a buildup of the pinewood nematode and the insect vector. Nevertheless some of the pine mortality might be avoided by periodic irrigation of trees during dry periods.

In summary, make sure a tree is actually dead before cutting it down. If you have sap flowing or green bark tissue, it’s not dead, only sick. Keep sending the pine wilt samples in if in doubt, but in some respects it’s a bit overdone.

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