Weed control and root maggots: making canola pest management strategies compatible

Published source details Dosdall L.M., Clayton G.W., Harker K.N., O'Donovan J.T. & Stevenson F.C. (2003) Weed control and root maggots: making canola pest management strategies compatible. Weed Science, 51, 576-585.
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This study is summarised as evidence for the following.

	Action	Category
	Delay herbicide use Action Link

Delay herbicide use

Four randomised, replicated experiments in 1999-2001 in Alberta, Canada (Dosdall et al. 2003) found root maggot Delia spp. damage was generally lower in canola Brassica napus sprayed with herbicide at late rather than early crop growth stages. Two experiments found lower root damage in plots sprayed at six-leaf (damage rating of 2.5) rather than four-leaf (2.3 rating) and two-leaf (2.2 rating) stages in one of two canola cultivars, when averaged across sites, years and other treatments. Another experiment found this effect for two out of three cultivars and a fourth experiment found plots sprayed at the six-leaf stage had lowest damage in 1999 and 2001 (ratings of 2.7-3.2, 3.1-3.4 and 3.0-3.4 in six-, four- and two-leaf stages, respectively) but no effect in 2000. One experiment found less root maggot eggs in plots treated at the six-leaf (0.8 eggs/plant) rather than four- (1.4 eggs) and two-leaf (1.6 eggs) stages for one of two cultivars, but another experiment found only slight differences. Canola seed yields varied but were slightly lower in the six-leaf (392-3,265 kg/ha) than the two-leaf (672-3,458 kg/ha) stage treatments in three experiments. Glufosinate was sprayed in three timing treatments replicated four times. Root damage was scored 1 to 5.