Advisory work, by its very nature, is an intermediary between the re search worker and those who apply the results of his research. The challenge of advisory work is to devise means of and find pathways for transmitting research results to the user, overcome the reluctance of the latter to change, and often combine novel ideas with well-estab lished traditions. Nowhere is this challenge greater than in farming. This is especially true in developing countries, where the gap in the educational level between research workers and farmers may be ex tremely wide. Moreover, village-level advisers...

The development of a crop, and therefore its health, is always the result of interplay between biological and environmental factors, as influenced by human agency. In other words, crop health is a highly complex affair. This book is concerned with only one group of agents affecting crop health, the pathogens, and not with animal pests or direct effects of physiological or weather factors. Even within this one group, however, the interaction of causal agents with environmental and biotic factors is highly complex. No less complex is the effect of cultural practices on the crop and its health....