CHEMICAL CONTROL OF BLACKLEG DISEASE OF CANOLA IN WESTERN AUSTRALIA

Ravjit Khangura1 and Martin J. Barbetti1,2
1Agriculture Western Australia, Locked Bag No. 4, Bentley Delivery Centre 6983, Western Australia, 2 Faculty of Agriculture, The University of Western Australia, Mounts Bay Rd, Nedlands 6907, Western Australia

 

 

Abstract

The efficacy of the fungicide Impact (a.i. flutriafol) was tested to control blackleg (Leptosphaeria maculans) and improve yield of canola (Brassica napus) cultivars with varying levels of blackleg resistance.† The trials were conducted at three locations (Mount Barker, Wongan Hills and Merredin) in 1996 in paddocks containing 1-4 year old blackleg infested residues.† The fungicide Impact was coated on a double superphosphate fertilizer and applied @ 400ml/ha (recommended rate) at seeding.† The disease was substantially reduced and the yield improved from application of Impact in most of the treatments at all locations.† The improvement in yield was variable with different ages of the residue.† The yield response to fungicide was greater under severe to moderate disease conditions than under mild disease conditions.† The rates of Impact were further evaluated in paddocks containing 3 year old residue in trials at the same three locations in 1997 and at two locations (Wongan Hills and Merredin) in 1998.† The fungicide was applied @ 200, 400 and 800 ml/ha.† In both years, blackleg severity was substantially reduced at 400 and 800 ml/ha but yield was improved only in some of the treatments.† A cultivar x fungicide interaction was observed in relation to the yield in all trials.† In general, susceptible to moderately resistant cultivars showed greater improvement in yield than resistant cultivars.† In 1998, various methods of placing Impact treated fertilizer were evaluated for their effectiveness in curtailing blackleg.† Drilling the fungicide coated fertilizer with the seed or placing it 2 cm below the seed were the most effective ways of reducing blackleg and improving yield in canola compared with side or deep banding.

 

KEYWORDS:† Leptosphaeria, flutriafol, fungicide, management, residue

 

Blackleg caused by Leptosphaeria maculans (Desm.) Ces. & de Not. is the most important disease of canola in Western Australia (WA).† Canola plantings in WA have dramatically increased from 35,000ha to 510,000ha during 1993-1998.† During this period an increasing incidence of blackleg has been observed.† As the area under canola and the amount of infected residues rapidly increase, management of blackleg is becoming more difficult.† In WA, blackleg is generally managed through use of resistant varieties and cultural practices including rotations, destruction of crop residues and distancing canola from the infected residues.† However, management of blackleg through chemical approaches has become an important component of blackleg management strategies in WA because of large-scale cultivation of moderately resistant varieties.† Impact (flutriafol) has been used in the eastern states to control blackleg at 1-2 year old canola residues (Ballinger et al., 1988a & b).† Impact has been found to be effective in partially controlling blackleg disease and improving yield in canola in WA (Khangura and Barbetti, 1997).† However, its efficacy at different rates and effect of fertilizer placement at various positions in relation to the seed and the efficacy of other potential fungicides need to be investigated.

 

Materials and methods

 

During 1996, field trials at three different locations, viz., Merredin, Wongan Hills and Mount Barker representing low, medium and high rainfall areas of the state were conducted to evaluate the efficacy of Impact (a.i. 250g/L flutriafol) to control blackleg.† Three commercial canola cultivars (Dunkeld, Narendra and Hyola 42) differing in blackleg resistance, were grown in paddocks containing residues from 1992-1995 canola crops (i.e.1-4 year old residues) to generate different disease pressures.† Fungicide coated double super (@ 100g a.i./ha ) or untreated double super as control were applied with the varieties at sowing.† In 1997 and 1998 trials were also conducted to evaluate the rates of Impact at Wongan Hills and Mount Barker representing medium and high rainfall areas.† Four commercial canola cultivars (Hyola 42, Narendra, Oscar and Dunkeld) of differing blackleg resistance were sown in paddocks containing three year old residue. Impact was applied at the rates of 0, 50, 100 and 200g a.i/ha.† In an another trial at Wongan Hills, various ways of placing fungicide treated fertiliser were evaluated.† Cultivar Karoo was sown in a paddock containing two year old residue.† The double super fertilizer coated with and without the fungicide Impact, was placed at 2 and 7 cm below the seed, likewise, at 2 and 7 cm sideways of the seed. The double super fertilizer coated with and without the fungicide was also direct drilled with the seed and also top dressed.† For all these trials, assessments for crown canker severity were made at the end of flowering and yields were recorded at the end of the season.

 

Results and discussion

 

Efficacy of Impact

There was a substantial decrease in blackleg disease severity and an increase in yield with Impact at all the residue sites at Merredin in all the three canola cultivars.† At Wongan Hills and Mount Barker, Impact had little effect on blackleg severity but increases in yield were still recorded at nearly all the sites.† The mean percent disease control and the mean percent increase in grain yield with Impact over the three sites at the 4 residue ages are given in Figs. 1 and 2. †A fungicide x cultivar interaction was observed in relation to the yield.† In general, the yields were greatly improved with Impact in susceptible to moderately resistant cultivars (Hyola 42 and Narendra respectively) compared to resistant cultivar (Dunkeld). A trial was also conducted at Mount Barker in 1998 to evaluate the efficacy of various systemic fungicides to control blackleg in canola. †Cultivar Karoo was sown in a paddock containing two year old residue and the fungicides Bayleton @ 0.3Kg/ha, Benlate @ 0.3Kg/ha, Folicur @ 0.35l/ha, impact @ 0.25l/ha and Sportak @ 0.5l/ha were applied as foliar treatments.† The first spray was applied at the above rate soon after emergence of the crop and the second application was done at the same rate three weeks later.† Impact as an in-furrow treatment at the recommended rate (400ml/ha) was also included for comparison.

 


Fig. 1† Mean percent blackleg disease control with Impact over three locations in 3 different canola cultivars (Narendra, Hyola 42 and Dunkeld) grown on residues of 1-4 years of age.

 

 

 


Fig. 2† Mean percent increase in grain yield with Impact over three locations in different canola cultivars (Narendra, Hyola 42 and Dunkeld) grown on different residues of 1-4 years of age.

 

Rates of Impact (flutriafol)

At Mount Barker the crown canker severity was significantly reduced in all the cultivars except Narendra at recommended and the higher rates of Impact compared with the half rate and control.† At Wongan hills, disease severity was significantly reduced in Narendra at all the three rates and in Hyola 42 at the higher rate, but the decrease in crown canker severity in other cultivars was not significant. The increase in the grain yield ranged from 5-82% in most of the treatments at Mount Barker and 1-48% at Wongan Hills.

 

Effect of placement of Impact treated fertilizer at various positions to the seed on blackleg

The percentage of plants with severe crown cankers was substantially reduced by more than 40% and the grain yield was improved by more than 950 Kg/ha by drilling the fungicide treated fertilizer with the seed compared to other treatments and the control.† However the treatment of placing the fertilizer below the seed at 2 cm was at par.

 

Efficacy of other fungicides to control blackleg

 

The crown canker severity and the percentage of plants with severe crown cankers was greatly reduced (50 and 20% respectively) with Sportak followed by Impact as foliar treatment and as inĖfurrow treatment compared with the other treatments and control (Table 1).† The yield was not recorded for this trial as this site was severely water logged.

 

Table 1† Efficacy of various fungicide spray applications on blackleg crown canker severity of canola cv Karoo

Treatment

Mean PDI

Mean %SCC

Bayleton 0.3Kg/ha

66

40

Benlate 0.3Kg/ha

70

41

Folicur 0.35L/ha

72

46

Impact 0.25L/ha

56

30

Impact in furrow

63

39

Nil

79

58

Sportak 0.5L/ha

54

21

PDI = Percent disease index

%SCC = percent plants with severe crown cankers

 

CONCLUSIONS

Impact has a role to play in managing blackleg disease in WA, especially where varieties of low resistance are sown in high disease risk situations.

 

ACKNOWLEDGMENTS

We thank the Grains Research and Development Corporation for funding this research.

 

REFERENCES

Ballinger, D.J., Salisbury, P.A., Kollmorgen, J.F. and Potter, T.D. (1988a).† Evaluation of fungicides, applied at sowing, for control of blackleg of rapeseed.† Australian Journal of Experimental Agriculture 28, 511-15.

Ballinger, D.J., Salisbury, P.A., Kollmorgen, J.F., Potter, T.D. and Coventry, D.R. (1988b).† Evaluation of rates of flutriafol for control of blackleg of rapeseed.† Australian Journal of Experimental Agriculture 28, 517-19.

Khangura, R. and Barbetti, M.J. (1997).† Blackleg monitoring and the role of Impact in-furrow for its management in Western Australia.† Proc. ĎEleventh Australian Research Assembly on Brassicasí, Perth, Western Australia, Oct. 6-10, 1997, pp. 16-18.