We all have those neighbours who many years ago planted what they thought was a small or dwarf conifer that has turned out to be a giant. It also causes problems as they need to be pruned, cut back and controlled. If you are not a gardener this is a massive job to tackle and many people just ignore them, but unfortunately they don't go away. In some cases they get bigger and uglier and take up all the space and block all of your light.
Conifers are generally good at protecting themselves against disease through tannins in their sap. But pollution and inadequate care will impact their natural resistance and make them susceptible to otherwise harmless infections.
Coniferous trees and shrubs are great when they occupy a very special place in the garden. There are many magnificent specimens, they look great in their own right. No fuss, just sit there looking green and gorgeous.
A lot of native conifers are fine but some conifers demand careful maintenance. Many have been introduced from exotic, far-off places and they rarely find optimum conditions for healthy growth. Many become sickly; their needles discolour and drop prematurely, and foliage that once covered the trees densely often begins to look spotty.
If you have a hedge made of conifers and some are brown and dry looking and the others are green in most instances, the causes for disease can be found in improper location and inadequate care. But disease may also be caused by animal-inflicted damage or by viral and fungal infections. The truth is only poorly and dying trees get diseases so you were probably missing something earlier than the colour change.
If you have a sad looking hedge like this, you are best dealing with it and taking it out - or getting someone to do it for you as some of these diseases will spread throughout your whole garden and in some cases the whole street.
It is a big job to face, but if you have tried several ways to treat them and you have had them looking sick and brown through all four seasons, you have to take them out or nothing will survive in your garden and the fungal/rust infection will prevent anything from being healthy, living or looking nice.