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Plant Diseases/white coating on leaves


I have 2 bees balms that have a white coating on its leaves. It does not rub off and now I think there is starting to be the same coating on a neighboring lilac and Joe Pye weed. Is this a fungal infection? What should I do? These are all new plants in a new rain garden.It has been pretty dry this year but I have been watering.

Dear Madeline,  Your bee balms have a condition known as powdery mildew, and yes it is a fungal infection.  Powdery mildew can develop during long stretches of damp weather, from watering the leaves of the plant and not just at the base, and sometimes it can occur simply by high humidity.  To treat this, you will need to spray the plant with horticultural oil which can be found at gardening centers.  Try to spray in the morning on a day that will be sunny, but try to avoid spraying any bees.  If your plant is flowering, you could remove the blooms before starting to avoid spraying any bees.  Spray the plant thoroughly until the plant is dripping.  After a few hours, the mildew will dry and begin to flake off.  You may need to spray the plant more than once a few days apart.  The cooler weather is beginning, and that makes this condition harder to cure, but try to do it on a warm day to get the best results.  You should spray the other nearby plants at the same time.  I hope this information helps you, but be sure to write back if I may assist you further.  Good luck, Melissa

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Melissa Johnston


Plant diseases, landscaping, tropical plants, roses, herbs, plant care, grafting, horticulture, plant identification, anything about plants I can likely answer.


35 years experience in various plant businesses, 1984 Certified Texas Master Gardener.

Master Gardener Association of Texas charter member

none as of yet, but I have a plant q&a book I am in process of submitting.

Magna cum laude graduate of Texas A&M, 1978

Awards and Honors
Plant growing awards, highest grade for Texas Master Gardener graduates.

Past/Present Clients
Past member of and was very highly rated. Owned landscape company in the past, Almost Paradise, and was very successful despite little equipment, no help, and no advertising. Lived well for two years until 9/11.

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