For the past few years, the growing tips of my apple trees start out looking OK, then in early summer the new growth wrinkles and sometimes turns partially brown. The shoots usually recover by late summer and start putting on more growth that looks normal. I've never seen any significant amount of aphids or other bugs hanging out in the distressed leaves. The branches do not seem to die back at all.

In addition to the tip dieback, some of the apple trees have been exhibiting overall decline(one died) over the last couple years, and some have large dark patches on the trunks and some major limbs that have a sooty appearance. I have seen little sign of this in the smaller branches. I do not see any sunken or hollowed-out areas like I see in pictures for apple canker.

Other potentially useful info:

- small hobby orchard that was established about 5 years ago

- zone 4a in a particularly harsh part of northern New York State. It's not out of the question that some trees are getting winter damage, but some of my trees should absolutely be hardy for this area

- A couple of the trees I have (like Liberty) are listed as "resistant" to fireblight, but show the same symptoms

- The soil is sandy with relatively low organic matter and excellent drainage. Soil is very high in magnesium and low in potassium despite annual applications of potash.

- I have been applying a small amount of 10-10-10 in late May of each year in addition to the potash

- I do not water the trees at all after their planting year

Any help would be appreciated.