Blackleg Control through Enhanced Straw Decomposition

Date: September 1997
Term: n/a
Status: Completed
Researchers: Dr. P.V. Blenis, P.S. Chow, and G.R. Stringam, University of Alberta
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Blackleg is an extremely important disease of canola and all of the control measures used have their drawbacks. Because the blackleg fungus survives only in the plant residues, researchers wanted to find out if it was possible that the incidence of the disease could be reduced if the rate of straw decomposition could be increased. Researchers at the University of Alberta conducted a three-year project from 1994 to 1996 to evaluate the potential for using selected cultivars, chemical amendments and decay fungi to enhance straw decomposition. Overall, the research did not find any significant differences in stem decomposition between cultivars or increased straw decomposition with either chemical controls or fungi. Overall, cultural controls for now seem to be the better strategy for increasing the rate of decomposition of straw.

Blackleg is an extremely important disease of canola and all of the control measures used have their drawbacks. Because the blackleg fungus survives only in the plant residues, researchers wanted to find out if the incidence of the disease could be reduced if the rate of straw decomposition could be increased. Enhanced residue breakdown may also reduce the need for deep tillage, extend the durability of resistance cultivars and increase soil nitrogen.

Researchers at the University of Alberta conducted a three-year project from 1994 to 1996 to evaluate the potential for using selected cultivars, chemical amendments and decay fungi to enhance straw decomposition. A number of different ways in which the rate of straw decomposition could be enhanced were considered: 1) varieties could be selected for rapid decomposition rates with due concern for lodging resistance, 2) chemicals could be applied to straw to increase the rate of breakdown, or 3) wood decay fungi, which have a remarkable ability to decompose lignified substrates, could be applied to destroy the canola straw.

The overall objectives of the project were to evaluate the potential of those three methods for increasing the rate of straw decomposition. Experimental straw material was obtained from canola regional variety trials established at Ellerslie, Alberta, including the roots and about 10 cm of stem from 23 cultivars of Brassica napus and 13 cultivars of B. rapa collected at random from centre rows. A total of 36 cultivars were tested over the three years of the project. In the field trials, the roots and stems were buried or left on the soil surface.

The results of the experiments indicated that B. rapa straw generally underwent greater decomposition than B. napus straw. However, the differences in straw weights between the species after one year were more due to differences in starting weight than in rates of decomposition. The differences in decomposition rate among cultivars within a species were not consistent, and when significant were fairly small relative to the large effect of straw burial. Species and burial effects differed slightly between stems and roots, but because roots are the more persistent, they may be the best experimental material for studies such as this.

Overall, the research did not find any significant differences in stem decomposition by cultivar within species. The study found that burial increased stem decomposition over surface application; however, roots underwent less decomposition than stems. Overall, none of the chemical treatments increased straw decomposition in a greenhouse test. And none of the fungi were particularly effective in either decomposing the straw or replacing the blackleg fungus. The best of the fungi tested were Cyathus and Coprimus as biological control agents. Surprisingly the wood decay fungi did not increase the decomposition of straw over fungi extracted from the canola plant. Overall, cultural controls still seem to be the better strategy for increasing the rate of decomposition of straw. Further research into chemical treatments and fungi assessment may provide some additional information and options.

Full Report PDF: Blackleg Control through Enhanced Straw Decomposition