"Disease in Plants" by H. Marshall Ward
Harry Marshall Ward, FRS, FLS, was a British botanist, mycologist, and plant pathologist. Using his expertise in the field, he wrote this valuable text which goes into great detail about plant health. Staring out with factors that constitute the viability of a plant, like its surroundings, food, and roots, he then describes the types of diseases that can afflict plants, their causes, and how they're spread.