Carol, BWs can be a weed - or a valued tree. Depends on your perspective and desires. If you're going to try your hand at harvesting nuts... Some will abort/drop early, well before they've sized up. Once the main crop begins to drop, it's really important to remove the husk material ASAP, before it gets black, gooey, and discolors the kernel. I just roll 'em underfoot to dislodge the nut from the husk - then dump the nuts in a bucket of water and stir vigorously, pouring off and replenishing the water until it comes relatively clear. Well-filled nuts will sink - 'floaters' may be poorly filled, but crack a few to be sure, before you discard them. Spread them in a cool, dry place to cure, for at least a couple of weeks (longer is even better) - right off the tree, they're not tasty. You can crack them with a hammer, but a bench-mounted vise or even a pair of vise-grip pliers are workable. A good hardshell nutcracker designed for that purpose is best, but may or may not be worth the investment for you. A pair of wire-cutting pliers and nutpick are very helpful in snipping here and there to relase kernel pieces. BWs have a flavor very different from 'English'/Persian walnuts (which, to me, have NO flavor) - BWs will add flavor and crunch to baked goods. Some folks like 'em, some don't. Most 'wild' BWs have fairly thick shells and low kernel percentage (in the 12-20% range); improved selections have thinner shells and kernel percentages approaching 40%.

I agree that a serious fruit gardener has enough to contend with without handicapping themselves by having chemical war waged against their trees in the soil. Also I believe that it is more than simply poisoning- established black walnuts are extremely competitive as their roots are extremely prolific in areas where they grow. I have recently established an orchard in the vicinity of these trees and the density of black roots in the area is remarkable. I have the area around each individual tree spaded with a King of Spades type solid steel, long handled shovel just as BW's show signs of growth. So far so good, but I'm sure the roots will eventually go under depth of spade work. As usual, it is the peaches that have been most sluggish- they tend not to compete well against established trees when transplanted. I've often thought that some kind of heavy fabric or copper screen set in the planting hole might be affective if it was part of the original installation.

You did dig and transplant while they were still dormant, right? I've rarely had problems with transplanting dormant bareroot 1-yr seedling nut trees, even when I've provided them with no appreciable aftercare beyond their initial watering-in, but they certainly benefit from mulching and supplemental watering, as needed, during the first year. I wouldn't be surprised with a 10-20% failure rate, but 70% is awfully high. As Resin indicated, try to preserve as much taproot and lateral roots as possible - they're reserve energy storage receptacles, providing the 'food' these seedlings need to re-establish root mass lost in transplanting and pushing new growth in the ensuing growing season. Generally, I recommend against any amendments in the planting hole - just crumble and replace the native soil that you initially removed; your seedlings' roots eventually have to grow in that native soil, so they'd just as well get on with it from the outset.

I raise rhododendrons and when I noticed some rhododendron plants dying, I noticed a couple walnut plants back in the woods behind the rhododendron bed with the dying plants. Since these were very tall established trees, I took the tact to girdle them. They still put out leaves the next 3 or 4 years, but dyed eventually. The rhododendron bed is now coming back. I lost some plants, but the rest survived. Now I go out each spring and pull out all new walnut plants. If you cut them off, it is best to apply roundup to the stump to keep them from sending up shoots. They will keep sending up new shoots from any roots left in the ground. They are planted by squirrels and grow rather quickly from the large black walnut nuts. They are easy to pull out when they first germinate, but the roots soon get very attached to the soil. Try removing all the roots if possible or spraying with roundup. The Juglone eventually degrades and the soil becomes useful. Some plants are not affected by Juglone: Here is a link that might be useful: Juglone Tolerant Plants