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Oak Problems

September 20, 2000

This article is one of those reverse-role articles. We have been seeing many oak problems in central Illinois, and I would like some feedback from you concerning occurrence of the problem in your areas. I will gladly summarize reports received and print a summary in the next newsletter. I am not referring to oak wilt, Verticillium wilt, iron chlorosis, oak leaf skeletonizing, or bacterial scorch. This problem seems to be something different.

The problem we are seeing is on oaks in the red oak group. The symptoms include bronzing and necrosis of the foliage, poor stem growth the last several years, a progressive decline over several years, and scattered dieback in the crown. The leaf symptoms are not always the same. They sometimes resemble an oak wilt pattern but are far less uniform. You might see a half-leaf symptom, and you might also see an edge burn or scattered blotches of necrosis. Wood does not show vascular discoloration. Cankers are not abundant on the wood. It is possible that a few trees have bacterial scorch, but symptoms donít always start on older leaves as they do with that disease. The pattern is scattered in the entire tree, not limited to one area that annually increases in size, as we see with bacterial scorch. We have tested a few samples (through AGDIA, Inc.), and they have been negative for Xylella fastidiosa, the causal pathogen of bacterial scorch.

I have been blaming root stress, possibly drought followed by flooding, but I do not have enough in-formation to make this claim with much conviction. Often the trees that are affected are 30- to 50-year-old trees that have been on the site relatively undisturbed. The trunks are not visibly injured, and lawn herbicides are not a consistent factor. One local arborist said that obscure scale was present on one of his sam-ples but not on several others.

This problem is not related to the leaf skeletonizer problem we discussed in issue no. 5 of this newsletter. You can tell me if you are seeing that problem (probably on your white oaks), but what I really want to hear about is this red-oak group problem. Give me the facts as succinctly as possible at npataky@uiuc.edu, or drop me a line at Plant Clinic, 1401 W. St. Maryís Rd., Urbana, IL 61802. Respond by Tuesday, September 26, if you want your information included in the summary in the next newsletter. Thank you for any help you have to offer. While you are at it, please comment on what we could do next year to make the newsletter more helpful to you.


Author: Nancy Pataky

 

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