Small Dark Dots Underneath Leaves Of Snapdragons - Knowledgebase Question

Kirkland, WA
Question by hawaii
September 19, 2002
Here in Washington State it is easy for Snapdragons to make it through the winter and grow well the following spring/summer.

My question/concern is the small black dots that are appearing on the underneath the leaves that cause thinning. What is this? It doesn't look like aphids because it's dark and I don't see anything moving.

Should they be treated with something come spring, or now, in the fall? I've got some really good colors and would like to keep them as healthy as possible. Also, could this be spread to other plants?

Any help you could give me would be appreciated.

Thank you.

Answer from NGA
September 19, 2002


What you describe sounds like the fungal disease called rust. Snapdragons are quite susceptible - especially at this time of year in the Pacific Northwest. Hollyhocks suffer the same fate. Rather than trying to treat the problem with fungicides, simply cut away the foliage of your snapdragons. If the winter weather is mild, new shoots will develop from the roots in spring and you'll have healthy new plants. Rust spores can splash onto other plants, so remove the foliage as soon as you notice the tell-tale spots on plant leaves, and you'll avoid the spread to adjacent plants.

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