Sorry, I don't know what's wrong with the leaves, but first of all, is the horse manure fresh? This will "burn" your plants, and will be too strong. You put manure in the ground around November time, and dig it in and let it "mature" through the winter. I feed my beans with Tomatorite, or any general liquid fertiliser suitable for vegetables. Anyway, using manure only encourages weeds. Horses graze, eat grass seed and the manure carries the seed into your bed. One way of stopping that is put manure into canvas sacks, and dunk them in a bin of water, let it ferment for a few weeks, then pour the fertiliser over the plants.