Looks like sooty mold, which is just that - a mold that grows on the excrement ('honeydew') of various sucking insects, such as aphids, scale or mealybugs. Although the mold itself is unattractive, it is really harmless unless it covers the foliage to the point where it restricts photosynthesis. Your real problem is not the sooty mold but what is causing its formation. You want to examine for the insect pests that are producing the honeydew. Note that they do not necessarily have to be on the plant itself but could be present on any overhanging plant material.

Agree with gardengal. Alphonse Karr seems to have this problem frequently. Spraying every couple of weeks for a while with something like Safer brand insecticidal soap should fix this.

My Alphonso had the same problem when I bought it and a year after planting. I tried copper spray without any success . I decided to just cut it off at ground level . I figured I'd either kill it or cure it. it cured it that was last year , this year its growing a lot with out the black.

tick-

Glad that worked for you, but there are less radical solutions than cutting it all to the ground. You may have used the wrong spray. However, it is true that even killing the infestation does not make the black mold disappear. This has to be cleaned off by hand or with a high-powered water spray. If you have the misfortune of another incident, try a pesticidal soap, or a spray of rubbing alcohol. It would be a shame to have to keep cutting your plant down to "cure" it.

That's what I was told to use by the bamboo farm I purchased I from. This stuff is 10 foot tall now. I am wondering though about my dwarf Buddha . We are in our drought season here in Florida . I have 10 stands of it and they are well established plants. They have pretty much dropped there leaves. Do you think they can go without water for maybe a month or two ?

In your climate, dropping leaves is not a good sign. I would keep them watered.

@ tick800, any clumper dropping it's leaves now is not good. Remember,bamboo is a grass and like any grass it needs some water occasionally to continue to survive.

The first signs that your bamboo is in distress is the curling leaves. This is the plant telling you it needs water and needs it now. The second sign is the leaf loss, and by then it may be too late, and the rhizome mass has dried out substantially and the plant no longer has energy to sustain life. If the culms turn brown they are most likely gone forever.

"For a more natural pesticide, use sprinkle coffee ground all through the clump several times a year. <--this works great for treating Asian cycad scale too!"

Unfortunately, this is just a garden myth. Used coffee grounds have a bit of a nutrient load (an N source) but there is NO scientific basis to support any effectiveness as an insecticide. They won't kill aphids or scale (or deter slugs or snails) and ants will just relocate or push the grounds out of their main traffic paths.

The Myth of Coffee Grounds.

Well I guess I and others are myth busters, because it works great here in Florida on my cycads and tropical clumping bamboos. But you know how the old saying goes, what works for one does not always work for another.

Just Google "coffee grounds tom broome" and you'll see lots of testimonial that coffee grounds work on numerous pests, especially Asian cycad scale.

http://www.cycad.org/documents/Broome-Coffee-2007.pdf