Efficacy of Impact® to manage blackleg (Leptosphaeria maculans) in canola

Abstract

The efficacy of the fungicide Impact® (a.i. flutriafol at 250 g/L) was tested for control of blackleg (Leptosphaeria maculans), and for improved yield and oil content in canola (Brassica napus) cultivars with varying levels of blackleg resistance. Field trials were conducted in 1996 in Western Australia at 3 locations (Merredin, Wongan Hills, Mt Barker) in paddocks containing 1–4-year-old blackleg-infested residues. The fungicide (400 mL product/ha) was coated on a double superphosphate fertiliser and applied at seeding. Blackleg was substantially reduced and the seed yield improved following the application of Impact® in most treatments at all locations except Mt Barker, where the fungicide had no effect on reducing the blackleg severity. The percentage reduction in blackleg severity with Impact® ranged between 18 and 59% and 1 and 43% at Merredin and Wongan Hills, respectively, in cultivars with different levels of resistance and exposed to infected residues of various ages. Likewise, the application of Impact® increased the seed yield by 40–322, 186–357, and 71–426 kg/ha at Merredin, Wongan Hills, and Mt Barker, respectively, on residue of various ages. Seed oil content was also improved following the application of Impact® in most treatments at all locations. The improvement in seed yield when using Impact® was variable for different ages of the residue, and was greater under severe to moderate disease conditions caused by exposure to more recent residues than under the milder disease conditions resulting from older residues. In general, susceptible to moderately resistant cultivars showed greater improvement in yield than resistant cultivars. The rates of Impact® were further evaluated in paddocks containing 3-year-old residue in field trials at the same 3 locations during 1997. The fungicide was applied at 200, 400, and 800 mL product/ha. Although blackleg severity was substantially reduced following application of Impact® at 400 and 800 mL/ha compared with 0 and 200 mL/ha, yield was improved only in some cultivars and at some locations.