Brown spots on oak leaf hydrangea leaves - Ask Extension
What are these brown spots on my oak leaf hydrangea leaves and what can I do about them? I did a spray with copper fungicide a couple days ago, but n...
Knowledgebase
Brown spots on oak leaf hydrangea leaves #872226
Asked June 08, 2024, 8:02 PM EDT
What are these brown spots on my oak leaf hydrangea leaves and what can I do about them? I did a spray with copper fungicide a couple days ago, but not sure if that is the answer.
Multnomah County Oregon
Expert Response
Thank you for your question. These spots appearance is consistent with the leaf spots described here: https://pnwhandbooks.org/plantdisease/host-disease/hydrangea-leaf-spots
Some are bacterial infections (Pseudomonas syringae); some are fungal (Phoma and alternaria). You would need a lab test to distinguish. If cultural controls are ineffective, then a copper fungicide may work. You probably applied it after the infection had already occurred, so it was ineffective. This type of fungicide is preventative, not curative.
I hope this helps. Good luck!
Some are bacterial infections (Pseudomonas syringae); some are fungal (Phoma and alternaria). You would need a lab test to distinguish. If cultural controls are ineffective, then a copper fungicide may work. You probably applied it after the infection had already occurred, so it was ineffective. This type of fungicide is preventative, not curative.
I hope this helps. Good luck!
