Rotting blooms on Dahlias

Asked September 19, 2017, 2:55 PM EDT

My dahlias have been blooming profusely all summer. They still have a lot of blossoms, but in the last few weeks the blossoms are rotting on the stem and not opening. Also the leaves have a whitish film and are somewhat shriveled. These are in pots that I over wintered in the basement. What might be causing these problems?

Ramsey County Minnesota dahlias plant health

1 Response

Thank you for the question. It's possible that the cooler, darker, wetter days we had prior to the last week have caused the buds to rot. Another possibility are thrips, tiny insects that burrow into the bud and leaves of many different plants and use their piercing, sucking mouth parts to feed and cause damage or death. You will have to look closely for them. Here are publications with more information: https://edis.ifas.ufl.edu/pdffiles/IN/IN105800.pdf
The whitish film could be several things. Examine your plants carefully and ask yourself the following:
Is the white film removable?
Is there any fuzzy or cottony texture in the white parts?
Is there any fine webbing visible, especially on the underside of the leaves?
And most important, do you see anything moving when you examine the leaves closely - tiny black, white, or red insects?

If possible, respond to the questions and include photos of the problems you are seeing and we will try to narrow down the diagnosis.
Thank you for contacting Extension.