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Pine Woes?

April 25, 2001

Recent warming has many enjoying gardening and the fresh outdoors. After clean-up and pruning chores are done, we often find ourselves waiting for danger of frost to lessen to start planting. I suggest that you take this time to inspect your pines. Two common disease problems should be addressed now, but be aware that they can be confused with other problems.

Sphaeropsis blight was discussed in the last issue. By now, you should have removed dead branches, dead branch tips, and fallen needles and pine cones. Be sure to keep those trees from drought stress. Another pine disease obvious now is pine wilt. It causes an entire, mature tree to die within a season. You may have noticed a favorite Scotch or Austrian pine turning pale green and then brown in a matter of months, and for no apparent reason: This is typical of pine wilt. The disease is caused by a nematode (microscopic round worm) introduced into the tree by the feeding of infested Sawyer beetles. The nematode remains in the wood, not in the roots as with field crops. It would be wonderful to stop this disease by controlling the beetle or injecting a miracle cure into the vascular system, but nothing is effective. We must remove pines as soon as they die to prevent spread of the pathogen to healthy trees. If you want to be sure these nematodes are present, sample the tree as you remove it, send the sample to the clinic with the ap-propriate fee, but get rid of the tree while you wait for results. This test is relatively quick (24 hours). Keep-ing the tree in the landscape lets the vector spread the nematode pathogen. Details can be found in Report on Plant Disease no. 1104, available in Extension offices or at http://www.ag.uiuc.edu/~vista/horticul.htm.

White pines are not affected by pine wilt; so if they are dying, itís something else. They have suffered in Illinois for many years due to hot, exposed, clay sites. Root rot may be involved with their decline: This is not an infectious disease but a problem of site and environmental stress.

If needles exhibit brown spots or brown tips, especially near the bottom of the tree, Dothistroma blight or brown spot diseases may be present. These are last yearís infection. New needles should be protected from infection this spring. Watch for information about these diseases in the next issue.

Many pines along roadways have been showing browning of needles, usually only on the side facing the road. Such injury is usually attributed to salt injury from salty mist blowing on the foliage. New growth should have a healthy green color.

Some insect problems can cause pine injury too, so look for evidence of insect feeding, tunneling, or insects themselves in affected tissues.


Author: Nancy Pataky

 

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