The effect of Cl soil fertility and plant nutrition on plant diseases has been the subject of numerous investigations over the past two-decades.    Oregon studies during the early 1980's (Christensen et al., 1981) on take-all root rot of winter wheat and Cl fertilization provided the catalyst for many of these investigations.  Chloride fertilization has been reported to suppress a number of diseases in different crop species (Table 1).  The mechanisms involved in these reponses, i.e. direct effect on the plant pathogen or increased host tolerance, have not always been clear.   What has been interesting is that some of the most important economic responses (yield or quality) to Cl fertilization have come in environments with considerable disease pressure.