I have a row of Laylandii planted last year, so far they are 3-4' high.
They were over run with weeds last summer and I sprayed carefully around
them with Round Up weed killer or so I thought. Some appears to have got
on one of the trees and the top half has gone brown and looks dead.

What's the best thing to do, cut off the brown or wait for new growth
from the brown stem?

TIA.