I have nine beautiful mugus lining my front walk. They had been planted about ten years ago. This year, one of them (in the middle of the row) has developed brown needles that are affecting about 30% of the plant. I tried some commercial sprays and insecticidal soap but nothing seems to work. Is this some kind of resistant insect damage or a disease? I would hate to have this spread to the others, especially if it is contagious. So far, none of the other plants show anything similar. Thanks.
It could be a spider mite issue which would need a spray of a miticide to kill them. You may also be spraying the insects at the wrong time, i.e., they may have already done their damage. This one Mugo Pine may need more room to grow or the soil there could be of a different consistency or it may get a different amount of water than the others.