For the last 30 years, I've had a 10' x 20' stand of bamboo at the corner of my driveway and street, grown for its ornamental value. Metrically, it's about 18 to 19 m² in area. Phyllostachys aurea, I think. It gets plenty of sun but, while the area receives good rain, the bamboo's position between street, driveway and parking bay means it stays relatively dry. For the last several years, some to most of the culms have grown well but immediately lost all leaves on the upper fifth of their length. Above 20 feet the patch looks like a forest hit by Agent Orange. I don't use herbicide on the patch but, hmmm, do use herbicide -- labeled for killing grass -- outside of the patch as part of my effort to keep bamboo from overtaking our entire garden. Where I see a shoot emerging outside the patch, I kick it over, or machete it. Then, as a kind of coup de grace, cover the stump with a spray of herbicide. Until writing out this question, I've assumed the die-back resulted from some kind of nutritional deficiency. Which still might be the case -- please make suggestions -- but now I'm wondering if my herbicide applications might have found their way back to the mother patch, and be causing the die-back. Suggestions?
I do not believe the herbicide is the culprit here. The damage from an herbicide would not begin at the top. I think you have Bamboo Mosaic Virus. There is no cure but heavy pruning can keep it at bay. All tools must be sterilized before and after any pruning takes place. Do not cut back infected shoots then move to healthy ones without sterilization. I am attaching an article that tells you more about bamboo and its possible issues;