High levels of grass weed control are required if canola is being used as a disease break for other crops. Canola can compete quite vigorously with many weeds, providing it has good levels of nutrition and is protected against insect attack. In pasture paddocks that are sown to canola, it is important to remove the broad-leaved weeds and silver grass in the previous seasons, to minimise their seed set. Pre-seeding strategies for controlling emerged weeds in canola using knockdown herbicides are similar to those for most other crops. In weedy paddocks, growers are advised to delay seeding until effective knockdown weed control is achieved.
Weeds can have a far greater impact on canola yield than delayed sowing.
It is essential that an adequate rate of knockdown herbicide is used before seeding, to ensure that potential transplants do not occur, especially if minimum or no-tillage seeding is planned. Trifluralin will also assist in suppressing both wireweed and fumitory. Incorporate these herbicides in a way that minimises the risk of wind erosion or wind blasting of emerging canola seedlings. It may suppress doublegees if applied at the highest label rates when the canola has at least four leaves. The herbicide choice should be part of a program to rotate grass herbicides in order to minimise the onset of resistance.