My mum’s leylandii are turning brown from the tips. In one hedge the effect is evenly all over - on the other you can see there has been more die back one one half and it looks flatter and kess leagy than the rest of the hedge.
Leylandii Turning Brown
Certified GKH Gardening Expert
This could be a fungal infection starting. Extreme cold can be responsible too, but this appears to be an infection starting. I would add wettable sulfur, and a little dolomitic lime to kill off anything in the soil, and recondition it to a proper balance.