Influence of crop rotation and tillage on production of apothecia by Sclerotinia sclerotiorum

Abstract

Field experiments were conducted at Marden and Arkell, in southwestern Ontario, from 1995 to 1998 to assess the influence of crop rotation and tillage on production of apothecia by Sclerotinia sclerotiorum. Treatments included five 2-year crop rotations of continuous soybean, corn–soybean, soybean–corn, winter wheat – soybean, and soybean – winter wheat in combination with minimum tillage, no tillage with residue chopped after harvest, or no tillage with no disturbance of residue after harvest. Crop rotation had a significant effect on the production of apothecia in all years at both sites (except for Arkell in 1998) and, in general, lower mean numbers of apothecia and (or) clumps of apothecia were recorded in plots planted with corn or winter wheat than with soybean. In all years, and at both sites (except Arkell in 1995), there were fewer apothecia and clumps of apothecia in the no-tillage treatments than in minimum tillage, although the difference was not statistically different in all years. Interactions between crop rotation and tillage were only significant in 1996 and 1997 at Marden where apothecia production was greatest in minimum-tillage plots planted with soybean, regardless of the preceding crop. Within the two no-tillage treatments, plantings of continuous soybean produced the highest number of apothecia and clumps of apothecia, and there was a 46.4 and 80.6% reduction in the numbers of apothecia at Marden in 1996 and 1997, respectively, in the no-tillage with chopped residue treatments when any crop rotation was followed compared with continuous cropping of soybean. The results of this study established that crop rotation and no tillage of soybean was the most useful combination of treatments that reduced the primary inoculum (e.g., apothecia) of S. sclerotiorum in infested soybean fields.