Bamboo Leaves Turning Brown?

I have a stand of bamboo (a Himalayan variety) that has done well for the past two years since planting them in San Francisco. A few months ago I noticed that the leaves were turning brown and the plants were looking stressed. I haven't changed what I've been doing for the past couple of years.

I believe that the plants are well watered, but not over watered. I thought that it may be frost damage, but with the spring leaves coming out, even a significant number of the small new leaves turn brown within a few days. The browning starts at the tip and works it's way back. Any ideas? Thanks.

By kel sheppey from San Francisco