Perhaps owing to these gonzo genetics, apples are remarkably susceptible to disease and rot. Their tender skin and light flesh are a haven for small creatures. Their trees embrace myriad molds, viruses, and fungi: apple scab, black pox, southern blight, union necrosis. For farmers and hobby gardeners, the business of apple-growing is not so much aiding the fruits in their growth as scrambling to ward off their demise.