Is this rust? - Ask Extension
Hello, I believe I have rust in my garden but I’m unsure. This is a lemon balm plant. The way I’ve been treating it is just pulling the affected p...
Knowledgebase
Is this rust? #905757
Asked June 14, 2025, 9:30 AM EDT
Hello, I believe I have rust in my garden but I’m unsure. This is a lemon balm plant. The way I’ve been treating it is just pulling the affected plants out. You just helped me identify that I have a four lined bug issue. But I’ve also thought I have rust. I hope these photos are sufficient.
Kent County Michigan
Expert Response
Hello Jessica,
Thank you for contacting Ask Extension.
About your lemon balm (Melissa officinalis), what conditions are you seeing that leads you to believe your plants have rust? I'm not seeing any of those symptoms, but that doesn't mean that there still could be rust symptoms on the underside of the leaves.
Rusts are somewhat easy to identify by their reddish-brown spores found on the underside of leaves. You may notice white or yellow spots on the top of the leaves at first, but the rust spores will develop underneath. Lemon balm can get rust if the conditions are favorable, but it is not one of the more common problems of lemon balm. The following article contains great information on rust disease.
The following is an excerpt about the diseases of lemon balm:
DISEASES. Mint rust, a fungus that generates small orange, yellow, or brown pustules on the undersides of lemon balm leaves, can be fought using a heat treatment in which the roots are immersed in hot water, cooled, and then replanted. To prevent mint rust in the first place, keep plants thinned for adequate air circulation within the plant, and remove dead stems.
Septoria Leaf Spot, a fungus that occurs in rainy climates, creates leaf loss for lemon balm plants. You can identify leaf spot by the circular spots with dark centers that appear on older leaves of plants. Remove infected leaves but avoid handling infected plants when they are wet to minimize the spread of the fungus.
Verticillium Wilt is a soil borne fungus that causes plants to wilt without warning. Infected leaves will begin to curl and quickly turn yellow and fall. If you notice verticillium wilt in your garden remove infected plants immediately and burn or dispose off the plant matter.
See https://stonepierpress.org/lemon-balm for complete article.
This is an excellent resource about rust disease:
https://extension.umn.edu/plant-diseases/rust-flower-garden#causes-of-rust-1169461
I'm sorry it has taken me a while to get back with you, but I want to be as specific as possible. The following articles contain information on lemon balm care and management.
-https://www.inaturalist.org/taxa/59901-Melissa-officinalis
-https://www.herbsociety.org/file_download/inline/d7d790e9-c19e-4a40-93b0-8f4b45a644f1
-https://extension.uga.edu/content/dam/extension-county-offices/columbia-county/anr/HerbsinSouthernGardens.pdf#:~:text=Rust%20 (See page 7)
If you would like to have your plant diagnosed for rust, you can take a sample to your county extension office:
Kent County
775 Ball Ave. N.E. Grand Rapids, MI 49503
I hope you find this information helpful, but please don't hesitae to contact us again if you have questions or need more information.
Have a great weekend!
Thank you for contacting Ask Extension.
About your lemon balm (Melissa officinalis), what conditions are you seeing that leads you to believe your plants have rust? I'm not seeing any of those symptoms, but that doesn't mean that there still could be rust symptoms on the underside of the leaves.
Rusts are somewhat easy to identify by their reddish-brown spores found on the underside of leaves. You may notice white or yellow spots on the top of the leaves at first, but the rust spores will develop underneath. Lemon balm can get rust if the conditions are favorable, but it is not one of the more common problems of lemon balm. The following article contains great information on rust disease.
The following is an excerpt about the diseases of lemon balm:
DISEASES. Mint rust, a fungus that generates small orange, yellow, or brown pustules on the undersides of lemon balm leaves, can be fought using a heat treatment in which the roots are immersed in hot water, cooled, and then replanted. To prevent mint rust in the first place, keep plants thinned for adequate air circulation within the plant, and remove dead stems.
Septoria Leaf Spot, a fungus that occurs in rainy climates, creates leaf loss for lemon balm plants. You can identify leaf spot by the circular spots with dark centers that appear on older leaves of plants. Remove infected leaves but avoid handling infected plants when they are wet to minimize the spread of the fungus.
Verticillium Wilt is a soil borne fungus that causes plants to wilt without warning. Infected leaves will begin to curl and quickly turn yellow and fall. If you notice verticillium wilt in your garden remove infected plants immediately and burn or dispose off the plant matter.
See https://stonepierpress.org/lemon-balm for complete article.
This is an excellent resource about rust disease:
https://extension.umn.edu/plant-diseases/rust-flower-garden#causes-of-rust-1169461
I'm sorry it has taken me a while to get back with you, but I want to be as specific as possible. The following articles contain information on lemon balm care and management.
-https://www.inaturalist.org/taxa/59901-Melissa-officinalis
-https://www.herbsociety.org/file_download/inline/d7d790e9-c19e-4a40-93b0-8f4b45a644f1
-https://extension.uga.edu/content/dam/extension-county-offices/columbia-county/anr/HerbsinSouthernGardens.pdf#:~:text=Rust%20 (See page 7)
If you would like to have your plant diagnosed for rust, you can take a sample to your county extension office:
Kent County
775 Ball Ave. N.E. Grand Rapids, MI 49503
Email: <personal data hidden>
Phone: <personal data hidden>
Please call first to see what day they do diagnostics.I hope you find this information helpful, but please don't hesitae to contact us again if you have questions or need more information.
Have a great weekend!
