Hydrangea Lime Light deformed flowers

Asked October 1, 2018, 11:04 PM EDT

Hello U of M extension, My name is Liz. I have a landscape design and maintenance business. I'm asking a question for a client who lives in the Plymouth MN area. We've noticed some differences in flowering on 10 Lime Light hydrangeas, in the yard. They bloomed late this year(Sept instead of July/Aug), and many of the flowers are small and deformed. Have also noticed some leafy areas where they should not be, and something that looks like witches brooms. The deformities are varied from plant to plant. The hydrangeas were planted in 2013. I prune about 1/3 back, each April and have used a garden 10-20-10 fertilizer. They are in part sun and have a drip irrigation system. Bark mulch, no fabric or barriers underneath. Have also noticed a bit more dead wood, each spring, and sometimes the roots come up to the soil surface. Have added about an inch or two of dirt when this happens. I've been advised to hold off pruning next spring and use a slow-release fertilizer instead. I believe there is more to it than just a lack of nutrients. Have also been told there isn't enough sun for them to flower. But this logic doesn't explain why the one shrub, in the sunniest part of the yard, is also having some deformed flowers. Did some research and am wondering if Aster Yellows, via leafhoppers, might be the cause of the deformities? The images online looked very similar to my photos. I haven't seen this on hydrangeas before; only on echinacea. Does anyone know if this is happening to other hydrangeas, here in MN? Thank you for your time, Liz P.

Dakota County Minnesota

7 Responses

Thank you for the question. I agree that a virus could be the problem and there are several known to infect hydrangea. The only way to know for sure is to submit a sample to the plant disease lab. Look here to learn how to do this: https://pdc.umn.edu/

As you probably know, there isn't a cure for this disease so I don't know if you want to spend the money on a definitive diagnosis. Infected plants should be removed and discarded. This Tennessee State publication has a good section on hydrangea viruses: http://www.tnstate.edu/extension/documents/Foliar%20diseases%20of%20Hydrangea%20FBG%20022916%20G1.pdf

I don't know if this has cropped up elsewhere in MN so I've asked an Extension plant pathologist for input and will forward to you when I hear back.

Thanks Anita, for your quick response. I'm looked through the article and didn't see any mention of Aster Yellows. I'm wondering if you can find out if anyone at the U has information on that specific disease. It would be good to know if this might be happening elsewhere in Minnesota. Thank you for your help!

Thanks for redirecting me! When I looked at the photos, I immediately thought "Virus"! Then, I failed to pay attention to the last part of your email-so sorry! I will amend my question to the pathologist to include aster yellows occurrences in the state.

No problem! Aster Yellows is a vectored virus so we are on the same page there☺

Thanks so much!

The following is the response from the Extension plant pathologist. I think the main point of her message is that viruses and aster yellows are both potential infections of hydrangea and you are not seeing anything terribly unusual.

"There are several viruses that are known to infect hydrangeas and aster yellows has been identified in hydrangea as well. Both virus in hydrangea and aster yellows occur in Minnesota. In order to determine which pathogen is causing the problem, she would need to submit a sample to the UMN Plant Disease Clinic (https://pdc.umn.edu). I agree that this is unlikely due to poor soil nutrition or low light. Malformed flowers and unusual growth can occur with both virus and AY infections. The recommendation for management of both diseases is the same, remove the infected plants and compost all plant material. Purchase a healthy plant from a reputable nursery as a replacement. As a result she will have to decide if it is worth the cost of the diagnosis to know what the problem is before she removes the plants.

Thank you for your response and information. Much appreciated! One further question: is it ok to leave the hydrangeas alone, for now, and see what kind of flowers they have, next summer?

Since we haven't done a sample to confirm which kind of virus, we are wondering if is ok to leave them alone, or will it spread further?

If it is Aster Yellows, that would be an insect-transmitted disease that affects plants individually, and would show up again, in those same plant areas, next season--but not necessarily spread unless there were more insects, next year?

The original master gardener who responded to you is unavailable at this time. If a plant has aster yellow it is best to dig out and dispose of. Aster yellow spreads plant to plant through insects and thus will likely infect other succeptable plants if the shrubs are left.