Black Spots on Sunflower Stems - What is it?

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iwn48 Burke, VA Jun 05, 2013

My giant sunflowers have some black spots on the stems - is this a fungus or something I should worry about?
If so, how do you get rid of it? Thanks.

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Diana_K Contra Costa County, CA(Zone 9b) Jun 05, 2013

Picture might be a bit blurry.

I see one spot, and maybe a dark area where the leaf joins the stem. Is that a problem area?
Are there more than these 2 black spots on the plant? I would try scraping off the one that is on the petiole. That is the specialized stem that holds one leaf.

Black things might be:
A bug called Scale. Many species. Hand removal when you just see the one is fine. If there are all over the plant it takes more work to get them under control. I do not see more, at this time, though.

Fungus or bacteria. There are several plant diseases that show up as black spots, but usually not just one or two spots. Often the conditions that favor the disease to spread allow many spots to form, pretty much all at the same time. So I would expect dozens or more of the same size spots all over the part that the disease likes.

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iwn48 Burke, VA Jun 08, 2013

Hi - There are black powdery spots in several places and then they eat a whole in the plant? Any ideas and what can I do about it. I have attached another photo on the
giant sunflower stems. Thanks. I have rows of sunflowers and don't want to loose them to something.

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Diana_K Contra Costa County, CA(Zone 9b) Jun 08, 2013

That looks like damage from a boring pest. The trick to controlling these is to spray when the adults are active, laying eggs. Once the larvae have burrowed into the stem there is not much you can do.

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