Reflections on space, time, and diversity

Farmers motivated and inspired me to pursue a career in plant disease epide miology. A taste for field observation and a need for reflexion led to a th eory of disease foci, which grow in space and time. Quantitative effects ar e modulated by qualitative factors such as race differentiation of the path ogen and partial resistance of the host plant. Moving to larger scales of o peration, within- and between-crop diversity become important. Diversity ma y be amenable to management. Whereas reductionistic experimentation will re main necessary to explain details, this paper makes a plea to use modem tec hniques for tackling complexity in crop protection.