Cupressus sempervirens Pyramidalis-Italian Cypress-Brown Patches

Hi all. First post. I have 4 of these beauties. They have been in about 2 years and were 5/6ft tall when planted. Soil was fairly heavy but I dug in plenty of manure and feed. Surface was mulched and they have been regularly watered. The area they are in can get breezy as we are a bit exposed being near a railway. They are now pushing 9/10ft plus and to me seem healthy apart from these brown dry/dead patches. Mainly nearer the base but some further up too. Is this aphids or too much/little watering? I have not treated, fed or trimmed  them  since planting but hope to find some pointers from you guys for a solution. They would be expensive to replace at that height. Many thanks. Rob