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

The impact of incorporating residues into soil and applying chemicals to st ubble was evaluated on canola residue decomposition and inoculum production by Leptosphaeria maculans during August and November 1994 and April and Se ptember 1995. Residue decomposition, measured as the loss in residue dry we ights, was more rapid in the incorporated residues than in the surface-plac ed residues up to the first sampling date but was similar in both treatment s 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 incubati on of residues on vermiculite at 16 degrees C for 4 weeks, higher pycnidios pore levels of L. maculans were observed in the incorporated versus the sur face-placed residues. Without the 4-week incubation, pycnidiospore producti on on the sampled residue was lower for incorporated residues for the first three sampling dates but not for the final sampling date. Treating blackle g-infected canola stem bases with liquid N (28-0-0) + glucose, urea (46-0-0 ), Roundtip(R) (glyphosate), Stubble Digest-All(R) powder, or a distilled w ater control had no effect on canola decomposition and sporulation by L. ma culans.