The impact of soil incorporation of canola residues and stubble application of chemicals on decomposition and inoculum production by Leptosphaeha maculans

Abstract

The impact of incorporating residues into soil and applying chemicals to stubble was evaluated on canola residue decomposition and inoculum production by Leptosphaeria maculans during August and November 1994 and April and September 1995. Residue decomposition, measured as the loss in residue dry weights, was more rapid in the incorporated residues than in the surface-placed residues up to the first sampling date but was similar in both treatments from the second to the last sampling dates. Averaged over all treatments, soil incorporation of residues resulted in a 40% weight reduction during the study compared with 27% for surface-placed residues. Following incubation of residues on vermiculite at 16°C for 4 weeks, higher pycnidiospore levels of L. maculans were observed in the incorporated versus the surface-placed residues. Without the 4-week incubation, pycnidiospore production on the sampled residue was lower for incorporated residues for the first three sampling dates but not for the final sampling date. Treating blackleg-infected canola stem bases with liquid N (28-0-0) + glucose, urea (46-0-0), RoundUp^® (glyphosate), Stubble Digest-All^® powder, or a distilled water control had no effect on canola decomposition and sporulation by L. maculans.

Keywords:

• canola
• blackleg
• residue
• decomposition
• sporulation