Some of the information in this article was drawn from that fine book. While I do lampoon some of the outdated advice on cleaning the nuts and extracting the nutmeats found in that book, it remains an important one in my library. Walnut trees are attacked by some 64 diseases and 296 species of insects and mites. I have used a fungicide in the spring as the leaves emerge, but usually just let nature take its course. Walnut pests in your area may be less or more significant.
Walnut trees suffer for want of nutrients in competition with grasses and weeds.
I do add fertilizer every 2nd or 3rd year about 10 inches deep around the drip line. In addition, walnuts benefit from trace quantities of zinc. If your soil is deficient in zinc, there are two easy remedies which can be applied on the same schedule. I don't think that I ever want that many nuts again in the same year. Nut production across the various cultivars is a bit of a mystery.