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Bee balms mildew #878256
Asked July 22, 2024, 12:56 PM EDT
Hennepin County Minnesota
Expert Response
Thanks for your question.
In answering your question, I’ll assume you are talking about powdery mildew. This is a large group of fungi that infects diverse plants, including bee balm. Rarely does an infection cause significant damage to a plant. Fungicides are only used as a last resort. See the following for some general information:
https://www.melindamyers.com/articles/powdery-mildew-on-bee-balm
https://www.extension.iastate.edu/news/yard-and-garden-bee-balm
As described in the above sites, non-fungicide procedures are the starting points for the management of powdery mildew on Bee Balm:
1). Ensure good air circulation: Space plants properly to allow for good airflow.
2). Water at the base of the bee balm: Avoid overhead watering to keep the foliage dry.
3). Remove infected parts: Prune and dispose of infected leaves and stems.
4). Use resistant varieties: Plant varieties of Bee Balm that are resistant to powdery mildew.
5). Apply fungicides: Use appropriate fungicides as a last resort if cultural practices are not effective.
If you do employ a fungicide, remember that it DOES NOT KILL THE FUNGI!! If you have a plant show the distinctive white covering of powdery mildew and you apply a fungicide, the whiteness will NOT disappear. Fungicides are used to prevent the germination of fungal spores and to prevent the spread of an existing infection. To put it another way, once you see an infection of bee balm, it is probably too late for fungicide application. When you said that your use of different sprays was not successful, my guess is that you applied them at the wrong time. Powdery mildew spores germinate rather early in a growing season. Apply fungicides to healthy green tissue early in this growing season, before bud break, or when white powdery mildew colonies first appear on leaves, buds, or shoots. For trees, spray early in spring when new foliage is emerging from buds. Be sure that the fungicide clearly states on its product label that it is effective against powdery mildew. As a Master Gardener of the University of Minnesota, I cannot endorse any specific commercial product. Nevertheless, see the following for some specific information:
https://ipm.ucanr.edu/home-and-landscape/powdery-mildew-on-ornamentals/pest-notes/ - gsc.tab=0
Good luck. Please get back to us with any additional, related questions. Thank you for using our forum.