Blackspot Survival in Soil and Stuble and Aerial Dissemination through the Season

Abstract

The amount of blackspot surviving on stubble and in soil in a long-term rotation trial at Turretfield, SA was determined over 4 consecutive seasons using a seedling bioassay. Infection from stubble was initially high but dropped to low levels after one year, while infection from soil inoculum declined slowly over 3 years. Hence soil-borne blackspot pathogens are an effective inoculum source for a longer period than stubble inoculum. Aerial inoculum was monitored over three seasons using ‘trap’ plants of 2-week old seedlings cv. Alma placed in the field at weekly intervals. The amount of inoculum varied greatly between years and sites, but in each season the aerial inoculum diminished rapidly after 70-80 mm of rainfall had been recorded. If this finding is reproducible across a range of sites it will aid in time of sowing decisions.