RELATION BETWEEN CROPPING FREQUENCY OF PEAS AND OTHER LEGUMES AND FOOT AND ROOT-ROT IN PEAS

The relation between the frequency of legume crops in a rotation and t he root rot severity in pea was examined in a field survey. Additional ly, greenhouse experiments were performed with soil samples from legum e rotation trials or from farmers' fields. The frequency of pea crops in current rotations proved to be much less than the recommended value of one in six years. The correlation between pea root rot and the num ber of years that pea or other legumes were not grown on the field und er consideration (called crop interval) was weak. Root rot severity co rrelated better with the frequency of peas or legumes in general over a period of 18 years, but the frequency still explained only a minor f raction of the variation in disease index. Some experimental data poin ted to the occurrence of a highly specific pathogen microflora with co ntinuous cropping of only one legume species, but this phenomenon prob ably does not occur in farmers' fields. In field samples, root disease index for pea correlated well with that for field bean. The survival of resting structures of pathogens such as Aphanomyces euteiches proba bly explains why the frequency of legume cropping has a higher impact than crop interval on root disease incidence. Pea-free periods and leg ume frequencies have a poor predictive value for crop management purpo ses.