Browning Leaves

[camikins]

Hi,

I've got an elm, with leaves that are browning. Not sure why - ideas? Too much sun, pest problem etc?

I'm in the pacific northwest, if useful. Normal daytime temperatures are around 20C / 70F. My soil is very porous (mostly turface) which generally works well for me with other plants. Water & feeding regiment is pretty standard, also consistent with my other bonsai, none of which are experiencing this issue.

Thanks