Matt, the "cold" thing is definitely out. That rattler idea is in play but he was thoroughly cowered when last seen. The "wet" thing sounds more plausible and something I had considered as well. Perhaps the waterings need to be spaced out a bit more - perhaps every four days instead of every 2-3. But then the torrential rains that South Mississippi is noted for having can't be helped. Perhaps some few are just destined to die. While in the field this afternoon, each leaf that was showing signs of blackening was snipped off. Last year, when one started showing signs of leaf blackening like the one in the picture, death was imminent although they often came back from the roots. So often did they do so that we quit thinking of them as dead and thought instead more along the lines of hitting the restart button on a video game.
BTW, we added 8 more today allowing us to break 500. To be precise, we now have 506 sets. Before leaving the field, a quick count revealed that we are almost exactly half done meaning the field will hold right at 1,000 trees. I recently read also that (1) my memory was a bit off and (2) on a 10' x 10' spacing, the number of trees is a tad over 400 instead of the 333 that I originally told y'all. That will translate into a field roughly 2 1/2 acres in size and, once completed, bring our total area in black walnut cultivation up to about three acres.