What is going on here? I have four pear trees planted "in one hole" and you would think there is some kind of invisible wall separating them into two pairs. It was the best of pears and the worst of pears:

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They are (from bottom left clockwise): Moretini, Beurre Superfin, Seckel, Warren. The first two look fine, nice green leaves. They have gotten a touch of mildew on some leaf tips but a spray of sulfur seems to fix that.

The other two have a more yellow green new growth which then begins to develop the symptoms seen in the pictures below.

Warren:
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Seckel:
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Last year (their first from bench grafts) the Seckel grew only about 6 inches before this leaf issue stopped it cold. I thought I had a failed graft but put it in the ground in the Fall anyway because there was growth from the rootstock so I thought I'd just try again. But the scion grew strongly once Spring came and looked OK (though never the deep green of the two other pears) until gradually it developed this "condition" and now growth is slowing again.In fact, buds that I didn't even know existed lower on the scion have begun to break.

Does anyone recognize this issue?