Advances in Plant Health Management in the Twentieth Century.
▪ Abstract Plant health management is the science and practice of understanding and overcoming the succession of biotic and abiotic factors that limit plants from achieving their full genetic potential as crops, ornamentals, timber trees, or other uses. Although practiced as long as agriculture itself, as a science-based concept, plant heath management is even younger than integrated pest management (IPM), and includes and builds upon but is not a replacement for IPM. Probably the greatest collection of success stories for plant health management is the number of diseases managed by cleaning up the planting material. The record for root health management is more mixed, with the loss or phase-out of soil fumigants, and practices such as crop rotation and clean tillage being replaced with more intensive cropping and less or no tillage. Perhaps the greatest scientific and technical advances for plant health management have come from the work aimed at management of the pathogens, pests, and other hazards that arrive by air. Flor's work on flax rust, which produced the gene-for-gene model, is possibly the most significant contribution of plant pathology to the life sciences in the twentieth century. Research aimed at the management of foliar pathogens is also the basis for modern theory on epidemiology, population biology, aerobiology, and disease prediction and decision-support systems. Even IPM arose mainly in response to the need to protect crops from pests that arrive by air. If the definition of biological control includes the plant induced or genetically modified to defend itself, as it should, then biological control has been the most significant approach to plant health management during the twentieth century and promises through modern biotechnology to be even more significant in the twenty-first century. Rather than "reducing losses," the advances are discussed here within the simple framework of achieving the attainable yield by increasing the actual and/or affordable and hence the average yield. Each of these four benchmark yields, as well as the absolute yield for crops, and their significance to the goals and achievements of plant health management are defined. Plant health management is a moving target, which I discuss metaphorically like an American football game, where one team is science and technology and the other is nature, where the S & T team is only beginning to know nature's rules while playing itself with the three sets of rules written to, respectively, satisfy the laws of economics, protect the environment, and gain social acceptance.