I have Phyllostachys aureosulcata 'Spectabilis' that I planted in 2007 in a very large container with a built-in root trench (a two-tiered system). The growth this year was spectacular -- 17 culms, with many taking interesting deep zigs and zags. This morning, I noticed that one culm had rotted on top, about four feet from the base; it wasn't rotted at the base, but it wasn't "right," either. One other culm has failed to thrive, but it was the last to break ground and I've seen that before.

None of the other culms look bad.

Any ideas?