Question

bad cotinus.jpg   QUESTION: I have a problem with distorted stems. The shoots become flattened and thickened at the end, and sort of swirl rather than grow straight. This problem affects cotinus and pyracanthus. The cross section of a cut stem shows the pith as very dark. There do not seem to be any pests on the plants. Powdery mildew? Aster yellows? Thanks VERY much for any information!

ANSWER: a.
Flattened stems can be caused by several agents, including mycoplasmas or phytoplasmas.  These entities are submicroscopic and would need to be examined in a lab with appropriate equipment.  Many of these agents are insect vectored. Virtually impossible to accurately diagnose based strictly on symptoms.

The discolored hollow stem in your photo can be the result of an insect present in the pith.  Many can eat the pith and may be boring types of insects- that may enter the stem at various places.

Regards
Steve

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distorted growth   QUESTION: Thanks so much, was afraid that was the case. I am terrified of these diseases because there is really no treatment, and the plants are mature in the landscape. I would  like to take the next step and take samples to a lab. Our county ag folks probably won't want to deal with this and I am willing to pay for the service. How do I find a lab?
Thanks again, most helpful.
p.s. attaching a photo of the flattened pyracanthus stem, just in case it is helpful

Answer
a:

Most states have a plant disease/plant health diagnostic lab that is affiliated with the land grant university in that particular state.  Your county Extension office should be able to supply that information to you.  Another route to take to find out is contact the Plant Pathology or Entomology department on that land grant university campus.  The clinic is usually run by these personnel.  Keep in mind that there may be a nominal charge/fee for some services.  Also, I suspect that your management options (if desired)for this (if it is caused by a biotic agent such as a phytoplasma etc.) will probably be limited to such things such as (1) selective pruning of affected tissues or (2) plant removal.

Regards

Steve