You have two common symptoms of aphids. The ants like to snack on the aphid's sticky secretions. Could be something else, but take a good look under the leaves for signs the the guys.

The dark deposits on the culm nodes are sooty mold. My Alphonse Karr also has it. Sooty mold is caused by sucking insects like aphids and scale which ants love. Systemic insecticides can control your problem but there are many other bamboos that are out there. Bambusa textilis varieties may be a better choice for you. They have similar chacteristics and are free of sooty mold. If you live near north Fl you can dig some in the spring. Rich

Thanks Bluesloth and orchidnuts for responding. Can I get
systemic insecticides at Walmart or Home Depot? Alphonse Karr is the only bamboo I have in my backyard. I mostly plant bananas and Angel trumpets, but I'm having second thoughts about the Angel trumpets because I'm worried that my neighbors' pets might get poisoned as they're planted just next to my fence line.