Soapy water and a high pressure jet of water. Will get rid of most of it but this will be a recurring problem. Another way to reduce it is to ensure good airflow through the boo.

My Silverstripe had this when it was located against the fence, however, when I took a division and planted it in the open it has not returned.

Insecticidal soap will help control the cause of sooty mold which is molds growing on the waste from piercing/sucking insects (homoptera). It will also help remove the mold itself when combined with a stiff spray of water.
You may need repeat applications.
Aphids seem to be more a response to poor culture conditions especially feeding high rates of nitrogen fertilizers which make for weak watery growth that they target.
Homemade insecticidal soap would be swishing ivory bar soap in water until it takes on a bit of a gray appearance.
Like any pesticide hot sun and pesticide together may be phytotoxic.

If you can plant any of the plants that attract ladybugs, they will be happy to graze through the aphids on your bamboo.