In article , Bert
wrote:

Aphids and mealy bugs will leave a honeydue deposit on the branch joint.
Ants come along and eat the honeydue and leave the black mold looking
deposits on your bamboo. This does not hurt your bamboo but it is unsightly.

I found an easy solution for the problem... On a whim, I took the power
sprayer to the grove. Knocked off most of the aphids and cleaned off a
lot of the sooty material. That seemed to tip the balance and the aphid
problem mostly cleared up after that. You can even add a little soap to
the mix and it seems to help and not hurt...

EMS