On 20/03/2016 17:37, Chris Hogg wrote:
On Sun, 20 Mar 2016 10:59:28 +0000, Steph wrote:

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.

If it really is just the top half, then there's hope, but it's no use
waiting for the brown bit to sprout. Leylandii don't shoot from old
wood, which is why you should never cut back a Leylandii hedge into
the brown interior, as you'll likely kill it. However in this case, if
it's just the top that's gone, then cutting out the dead wood will
allow the living part lower down to grow up and fill the space. Of
course, rather than just having a single stem or trunk, you'll have
several, although one may eventually dominate. You could put a stake
in and deliberately train one of the lower stems into an upright
position, when it will become the leader and grow away.

I'd be inclined to dig it out and replant, though it does depend on how
close you planted them and how tall you want your hedge.