A disease caused by the fungus Pestalotia, which produces browning of the foliage of conifers. Although other factors can cause the same symptoms, check for small black spots on the leaves. These are the fruiting bodies and as the spores are released they become holes or brown pits.
There is no control apart from cutting out and destroying all of the brown foliage. The problem has probably arisen due to the plant being under stress such as dryness at the roots. This could be because it has outgrown its site or the roots may not have grown out well enough from the original rootball when planted - it iS important to tease out or cut roots which are growing in a circular direction, following the contours of the pot. Recent practice is to dig a square hole when planting, particularly in hard ground, so any roots venturing out are more likely to go straight rather than do a u-turn and follow around the sides as they might in a round hole.
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