Conifer Hedge - Does Potassium Feed Prevent Die-Back?

Normally, at this time, the conifer hedge has several dead patches from the previous year, plus occasional winter damage. Not this year. Although there is slight frost damage, it's still completely free from die-back. Why?

I'm not sure. But I think feeding last year with 'Phostrogen Plant Food', a highish potassium feed (14-10-27), has much to do with it. I think the potassium has hardened the foliage, making it less attractive to insects and fungal disease.

I am still not really sure what causes die-back, even after much research. There seem to be several theories, ranging from suffocation through to disease and aphid attack. The trouble is that by the time the symptoms appear the causal agent is long gone. I currently think it's aphids, since the birds start feeding on the hedge around this time.

I applied the feed with a hosepipe applicator.

TREATING THE DIE-BACK
If you're wondering what the holes are for, they're where I dug out the last lot of die back. I have found that after cutting out the dead tissue back to the stems, re-growth occurs and the holes fill in. However, it's very important not to cut TOO far back. You want to be able to see at least a glimmer of green life.