Epidemiology: A Science of Patterns

During the twentieth century disease detectives progressed by jagged leaps in understanding patterns of plant disease. With ladders, airplanes, and automatic traps they observed airborne spores, and with meteorological theory they explained takeoff, flight, and landing. They analyzed the grand, logistic rise of epidemics and the roles of horizontal versus vertical resistance. From early experiments on the details of life cycles and weather, they simulated epidemics with new computers. Early in the century they revealed genetic diversity with differential varieties and late in the century with differential fungicides and DNA. They learned the interplay of pest, photosynthesis, and supply and demand to reckon loss. Integrating observations of pest, host, losses, and weather, they placed winning short-term bets for farmer and environment on whether to spray. In the twenty-first century, their goal can be analyses so sound that the world can securely place winning long-term bets.