FIELD EVALUATION AND THE IMPORTANCE OF THE ASCOCHYTA COMPLEX ON PEAS

Abstract

Mycosphaerella pinodes Berk, and Blox. Vestgrn. and Ascochyta pinodella Jones were found to cause serious yield losses in the field. Although a higher percentage of seeds became infected with Ascochyta pisi Lib. than with either of the fungi referred to above, yield losses were considerably less, This finding is important in setting disease tolerances for various grades of seed since in the past arbitrary scales for these three organisms have been set without any knowledge of the relative importance of seed infection to field epidemiology. Only races III and IV of A. pisi caused significant losses in yield. Cycloheximide (100 p.p.m.) applied as a spray in the field significantly reduced seed infection by A. pisi but also reduced seed germination. Phygon 50W and griseofulvin 50W did not reduce germination but reduced seed infection considerably although not completely. Granted, preliminary results suggested that certain chemicals gave a selective control of the races of A. pisi, but this phenomenon could not be further demonstrated because of secondary infection in the field.