Looks a lot like my hallertauer and fuggle. They're in a sliver of soil next to the driveway and there's also a blue spruce nearby....in other words, not ideal soil. Mine do that for two reasons, they're stressed because they're not getting the nutrients they need (I think the spruce tree also acidifies the soil too much) and both years I've had them, they got spider mites. Have a really really close look at the stems lower down - you should see tiny green things moving quickly if you have mites. There will also be a whisper thin webbing under the leaves.
For mites, add a fair amount of manure. I read somewhere that well rotted manure will have predatory mites. I added manure this past year and while I still had mites, they weren't nearly as bad as the year before. I also added a fair amount of soil "sweetener" (to raise the pH to counteract the acidity of the spruce needles). I also fertilised them more often this year than last. This year I still had browning but it wasn't as bad as last year.
I also tried spraying the plant with a concentrated tobacco and dish soap solution last year. That did kill the mites, but not all of them. It just wasn't possible to get every nook & cranny with the spray. I boiled some pipe tobacco and strained the tobacco out. I then added a very small amount of dish soap to act as a surfactant so that the solution would spread out and cover everything instead of bead up.
