What is the black residue on the leaves of my gardenia shrub? It comes off when I wipe it. How do I treat it?
Thank you in advance!
Most likely sooty mold which is secondary to honeydew excreted by one or several insects.
On a gardenia, I'd suspect mealybugs, aphids, whitefly and/or scale.
Once you find the critters,you should treat them.
Thank you Jean001. I will inspect the foliage for bugs. Hopefully the blooms will not be affected.
In the South, it's often said, "if you have gardenias, you WILL have whitefly."
I have found Bayer's systemic insecticide effective in treating whiteflies on Gardenias (pricey though)
Is it the same as Bayer all-in-one? I recently purchased it for roses.
Yes to the Bayer all-in-one.
Sooty Mold, yes...
The all-in-one products contain fungicides, insecticides, and fertilizers and/or miticides....and are not the same product as the Bayer's systemic pest control for shrubs. I'd advise against using the former, unless you actually have all of the above problems.
Once you've identified the pest, let us know! Or...if you aren't sure what it might be post an image or give us a good description so that we can ID it for you.
Once you can get control of the critter, the sooty mold will go away on its own.
Thank you all for your recommendations and advice!