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Disease Update

July 7, 1999

There has been a steady stream of various plant diseases at the Plant Clinic this summer. One of the more common diseases of ornamentals in the last two weeks includes oak leaf blister, discussed in issue No. 4 of this newsletter. We are seeing this on many oaks, usually with just scattered puckered lesions on the leaves, and not harming overall tree growth. Oak wilt (issue No. 7) continues to rear its ugly head in a slow but steady stream of samples. Donít forget to send oak wilt samples on ice if at all possible; this process will likely save you resampling time and energy. We have seen a dieback of spruce branch tips that is not associated with any pathogen. It is not caused by Cytospora canker or any needle cast that we can find. It has occurred particularly on dwarf Alberta spruce and may be an environmental, site, or root stress problem. Dutch elm disease (issue No. 8) has been very common this year from both municipalities and homeowners. Many bedding plants have been found to be infected with Rhizoctonia root and stem rot (issue No. 8).

Author: Nancy Pataky


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