In over fifty years of studying plants, Francis Chaboussou observed that a plant's nutritional state affects it's susceptibility to both insect pests and diseases. His theory of thrombosis is that "the relations between plant and parasite are above all nutritional in nature".
Technically, he argued, plant enemies depend on reduced sugars and free amino acids in a plant's sap, both of which are results of heavier fertilization with nitrogen, a practice which has become more common in the last century.
Chabousso's book, Healthy Crops, is not light reading. He details his observations and then gives multiple examples with technical information.
Unfortunately, this is part of the reason he and his contributions are essentially forgotten.