My first guess would be black sooty mold. I'm gardening in Charleston, too, and I sometimes see scale on the leaves of castiron plant cause serious black sooty mold. If you don't observe any scale or other insects on the cast iron, check the plants directly above. The honeydew these sucking insects drop can really make a messy culture for the BSM.

Cast Iron is pretty darn tough so you have several options. If the insects are on the cast iron leaves, you can spray them with some horticultural oil on them afer remooving most of the BSM w/ a jet of soapy water. Wait until the temps aren't expected to drop below 40 dgrees for a few days before the oil treatment to avoid damaging the plants. Another option, especially if it is a major infestation, is to cut all or most of the leaves off and wait until spring for them to put out new foliage. Then spray again in March-April with hort oil to get any of the insects that survived the winter. Cast Iron plant's roots/rhizomes are tough enough to survive a major pruning. If the source of the honeydew is from another infected plant, spray the CIP w/ a jet of soapy water to remove the BSM and the other plant w/ the same oil treatment as explained above.

Best of luck,

Bob

Thanks Bob,

Well I went out and looked and it seems that the BSM is all over everything under this tree. Ivy, azaleas, grass everything. I just noticed it first on the CIP.

The tree isnt anything spectacular..I think it is kinda a trash tree that I can cut down, which I was planning too anyways. A smaller tree under the live oak canopy.

I will go and try to wash off the BSM.
thanks so much!!

Alison

If it is black sooty mold (and it sounds like it since it seems to be on everything in the vicinity), washing it off won't do anything to solve the problem. You need to figure out what insect is the culprit and where it's hanging out. There are several different kinds of scale insects that affect oak...but so do aphids and other honey-dew producing critters.

BSM will never go away until you get the insect under control. If you do that, then it will quite rapidly begin to flake away on its own, though water sprays can help.

I did see some little white bugs on the leaves of the Cast iron..what can those be??
I am such a garden newbie..

Most likely scale, though I'm not sure which one. The horticultural oil treatments will likely get rid of them. They have probably 'hardened off' for the winter making it tough to get rid of them until Spring. When the temps. increase in late March- April, the young 'crawlers' will be on the move. This is the stage when they are most vulnerable to the oil spray. Another treatment with the oil in the Fall, before they've hardened off, would be wise. As rhizo 1 stated, you must eliminate the insects that are dropping the honeydew to prevent future black sooty mold.