Tony Dickerson problem solves
QWhat’s making brown patches appear on my conifer hedge? Tom Butler, Dunmow, Essex
AThis can be due to a number of different causes. These range from pests and disease to environmental reasons and even routine operations, such as trimming it. Evergreens can be slow to show symptoms so the cause of your brown patches could’ve occured months ago. Unfortunately, most conifers won’t sprout from old wood so rectifying the damage can be a problem.
Browning at the bottom of the hedge may indicate drought stress. Many areas of southern and eastern England have had less than a third of average rainfall this year. Mulching in early spring and watering thoroughly once a week in dry spells will help but may not always be practical or affordable. Salt may be a cause along roadside hedges in colder areas. Brown patches spread throughout the hedge are most likely caused by conifer aphids, which are active from spring to autumn. Unlike most aphids, these species inject enzymes into the plant that can cause shoot death. They’re difficult to detect and you need to look inside the hedge. Shake yellowing branches onto a bit of cardboard and check for evidence of the aphids or their cast skins. Treat with a systemic insecticide. There are a couple of fungal diseases that attack conifers, too. Pestalotiopsis dieback may occasionally cause brown patches but this can be difficult to diagnose. Look for tiny, black, fruiting bodies scattered over the affected foliage.
Coryneum canker can cause branch dieback. Pruning out the affected shoots will reduce the number of spores available to set up new infections, but avoid pruning during prolonged wet weather. Remember that many conifers won’t produce new growth if they’re cut back hard into old growth.
There aren’t fungicides available to gardeners with specific recommendations. However, Bayer Fungus Fighter and Scotts Fungus Clear Ultra are labelled for the control of a number of other diseases on ornamental plants, and could, therefore, be used legally on conifers (at the owner’s risk).
After conifer aphid, the most common cause of conifer browning is trimming too hard or too late in the season. Most conifers won’t shoot from old wood and need to be trimmed lightly. The best time to do it is before the end of August, because later cutting often results in soft new growth getting caught by the cold.