Problems with brown patches on Leyland Cypress hedges seem to be increasingly frequent. Hedges which had grown happily for many years develop brown areas which can vary from a few inches across to several feet. Hedge owners are then faced with a dilemma. Can the hedge be saved or improved or must it be removed entirely.
The Royal Horticultural Society (http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=132#top ) suggests that there are two major reasons why these patches might appear – attack by aphids and fungal diseases. Damage caused by aphids develops in late spring and summer and is found more often at the base of hedges though it can develop at any height. The browning can develop long after the aphids have left the foliage. The RHS suggest that spraying can be effective if the aphid attack is caught early and that some regrowth of new green shoots is possible. As a general rule however growth of new green shoots on brown conifers stems is slow if it happens at all.
Fungal disease is also a common cause of brown patches. Over enthusiastic hedge trimming, especially at times when a hedge is stressed, may increase the likelihood of die-back. They suggest that trimming in April, June and August is safer than in autumn. They especially suggest that you don't trim in hot or dry periods or in the autumn and that you never cut into old wood but only trim the outside growth. By old wood they mean thicker stems deeper into the body of the hedge. Feeding and mulching of the hedge in late winter, in preparation for spring growth, is recommended.
With an established hedge there may be nothing significant to be done to remove the brown patches and it could be necessary to take the plants out entirely. To replace the removed plants can be a difficult matter as the roots of an old hedge will be extensive and they will have removed most of the nutrients from the ground for quite an area around. Full removal of the stumps and replacement of the surrounding soil is the most likely way to provide a decent environment for a new hedge to grow. This might need the use of a mini-digger and is likely to involve professional landscapers. As replacements you should consider tough evergreen hedges such as Laurels, Portuguese Laurels or Western Red Cedar which would grow relatively quickly. Ivy screens are an option where an instant evergreen fencing/hedging solution is needed which will stay at around 2m high. Yews may also thrive and provide excellent formal hedges long into the future. All are less likely to suffer from the problems which Leyland Cypresses are prone to.
