Hello Anastasia,

Thanks for posting your question about your hydrangea plantings. This is indeed an interesting challenge. You mention virus as an affecting pathogen possibility. Perhaps. Annabelle hydrangeas in our area are usually fairly-free of biotic problems like viruses, fungal issues, or insects, so your photos are challenging. We fully understand your concern about the potential for losing beautiful hydrangea plantings.

Let me list various possibilities, after covering what we see in your photos.

The “muting” of the flower panicles, and the leaf growth distortions, are obvious. One would not know at first glance that these are hydrangea flowers. In the photos there is the appearance of inter-veinal chlorosis (lack of chlorophyll processes leaving yellow leaf tissue) in adjacent leaves including some inter veinal necrosis (tissue death). There is some “fibrous material” in one of the photos between leaflets that can be webbing. While there is some intermediate leaf “puckering”. The older leaves do not seem as much affected.

We don’t know much about your practices for irrigation, fertilization, chemical treatments nearby such as herbicides, or the nearby environment which will change one’s guess. Or the history thereof. From a photo of this type of plant problem only guesses are possible.

The symptoms which appear in your photos could be from virus infection, from mite feeding (more specifically eriophyid mites, which require a microscope for identification, a phytoplasma infection (similar condition to aster yellows), from a nutrient deficiency, or from recent herbicide drift.

The definitive information we could find on viruses on hydrangeas did not present the same as your photos. Eriophyid mites on hydrangeas seem to be rare. Nutrient deficiency or herbicide damage would likely show more broadly distributed symptoms.

You have no doubt looked at links like this one

https://www.tnstate.edu/extension/documents/Foliar%20diseases%20of%20Hydrangea%20FBG%20022916%20G1.pdf

Nevertheless, at this instant we are partial to the eriophyid mite explanation, because the distortions are consistent with those seen on other type of plant species, and because of the appearance of webbing in the photo. But this is a photographic guess at this time. Photos only go a short ways into diagnosis and unfortunately the Boulder County sample clinic is closed this summer. This is to our chagrin as well as yours.

It is important to perform the correct identification because treatment for eriophyid mites differs from viruses, from phytoplasma, and similarly for the others.

Good samples are required for proper diagnosis. Please see:

https://extension.colostate.edu/docs/pubs/garden/07246.pdf

We strongly recommend that you submit a real fresh plant sample personally to the Jefferson County Fairgrounds for immediate diagnosis. There is a form to complete with your practice information and history of the plant bed, and a modest fee to be paid. Please call ahead for the latest COVID instructions and office hours. The following web page lists the directions, the forms, and the phone number.

https://jeffco.extension.colostate.edu/horticulture/clinic/

You will receive an excellent diagnosis and sage management advice from Jefferson County.

Sincerely,

Boulder County Diagnostics Team