The leaves are curled up on all my apple trees. Some with as much as 60 % bark loss from SW disease, to newly transplanted young trees to second leaf trees on seedling rootstock. The later should have well established roots and few leaves to support. Yet leaf curl is about the same on everything. They’ve all been watered adequately, we’ve had rain, this is the norm here, and my apples bear every year.
I don’t think it’s SW disease or many of mine would be dead.
Some rootstocks can have issues with crown rot. That’s water related. SW injury is as described above.
This is from my own experience. My leaves curl because of too much heat and lack of water. Young leave will curl more than the older leaves. If there are root damage or trunk damage, then water and nutrient can’t get to the top. So leaves will still curl because it lack water or nutrient. If it’s insects damage then it shouldn’t effect the whole tree, unless you was sleeping on the job. Mildew will make the leaves curl too, but it shouldn’t effect the whole tree. At least not right away. Any disease that prevent water and nutrient uptake will make the leaves curl too. My environment is hot, so under watering is the least of my problem. So, environment my play a role too.
Observation is your biggest asset. One time the tip of my apple tree didn’t sprout out. Once it did, the leaves was very small. It curl out and soon die. upon my observation, the graft union was drying out. After cutting out the graft union for further inspection, not only it was drying out some part of it was like sandy. I suspect borers kill the graft union and preventing water and nutrient to the top.
