Q: A patch of bamboo 3′ wide and 20′ long just up and died on me this summer! I sprayed no herbicides nearby. It provided privacy between my den side windows and a neighbor’s garage. I do have hope, though: there are 3′ tall sprouts coming up under the dead stalks.
A: I think you’ve witnessed a normal bamboo phenomenon: after it blooms, it dies.
Your pictures clearly show the grassy flowers and seedheads of bamboo.
Fortunately, as you’ve observed, the whole plant doesn’t die. The underground roots immediately begin sending up shoots to replace the ones that went away.
Knowing how fast the plant grows, your privacy should be restored by the end of next summer.