A few days ago we discovered that the Black Walnut tree in our yard had unsightly bumps on the top side of lower-branch leaves. We learned, much to our surprise, that this was due to an infestation of gall mites. Yet the problem had been hidden and unseen from the ground; we only discovered the disease when we trimmed off a low-hanging branch. How deceiving! From a distance, everything looked just fine: thick leaves and abundant growth. Yet our tree had been getting stealthily infected without us even being aware of it. Black Walnut trees are particularly susceptible to gall mites. The problem is exacerbated when there is thick, unpruned foliage accompanied by a lack of rain. The combination of these two factors help the incubating mites to spread as they irritate the lower branch leaves; the ones that get the least amount of rain because of the thick covering of branches above. Not enough air and space between branches, and not enough rain water, help the mites to get a footh...