Nancy Taylor of the C. Wayne Ellet Plant and Pest Diagnostic Clinic reported that parts of or entire landscape plants are dying from various types of wilt diseases (e.g. Dutch elm disease (Ophiostoma ulmi ( formerly Ceratocystis ulmi)) and Verticillium wilt (Verticillium albo-atrum and V. dahliae)). Invariably, there will be clientele that will want to know which wilt disease or want to verify that it was a wilt disease that killed their plants. Nancy is happy to identify the cause (for a fee), but to be able to isolate the culprit she must receive an appropriate sample taken from the proper part of the plant.
Even though the most obvious outward symptom of a potential wilt infection is the browned, dangling dead leaves at the tips of branches, this is not the best place from which to collect a sample for analysis. Typically, the "clog" that produces the wilt of the leaves is found several to many feet lower in the plant. A sample consisting of just the branch tips with the leaves attached usually does not contain the disease causing organism. Thus, nothing can be isolated from this tissue to help in identifying the culprit. This could lead to a false negative result for one of the wilt causing pathogens.
An appropriate sample for analysis should be taken from deeper in the plant. Nancy recommends sending a sample composed of branches that are minimally 1/2" or bigger in diameter and about 10 - 12" in length. A sample should be represented by 10 - 12 of these sections from a branch that has recently developed the wilt symptoms. Sending the tips of branches with the wilted leaves along with the above described branch sample does not hurt, but it is the larger diameter sticks that really count. For more information about proper sampling and CWEPPDC, visit the clinic's web site at: http://ppdc.osu.edu/submit-sample/landscape/woody-plants .