I have been converting my yard to native plants. For the most part all plants are thriving and very healthy. As part of that transition, I do not use any chemical fertilizers or insect control. Among the native plants are 3 small bitter cherry trees (1 in the front, 2 in the back) that did not appear super healthy when planted Fall before last, but they keep surviving and came out with more leaves this Spring than last. I've noticed recently though, that all three trees have developed a strange tight curling of the branch tip leaves -- still green, not limp or wilting, but they do look distressed (photos attached), and now showing a number of yellow leaves. Maybe evidence of aphids or similar insect? To add to the mystery, this evening I noticed a red-flowering currant, maybe about 30 feet away from the bitter cherries, has what looks to my untrained eye to be a similar affliction on the tips of almost every branch. Maybe unrelated. The currant has been extremely healthy all Spring and was planted 3 years ago. Both cherry and currant are showing some yellow leaves. We have had a very mild Spring with intermittent rainfall and irrigation. What could be causing the tight curling of these new leaves? Any insight much appreciated!