A second in-crop herbicide application is not usually needed when the crop is well established, competitive, and ahead of the weeds. However, it may be justified when:
The crop is uneven and late-emerging canola is behind a new flush of weeds
Weed pressure includes tough species like narrow-leaved hawk’s beard, round-leaved mallow, or Group 1–resistant wild oats.
Weeds are abundant, at a similar stage or ahead of the crop, and the canopy hasn’t closed.
Weeds could impact grade potential (ie: cleavers).
Ask: how effective was the first pass? What might have compromised control on pass one? What weed species now need control? What products should be used and at what rates? How much time between passes? What stage is the crop? Should I leave a test strip? (answer: yes!)
(A second pass of herbicide - critical or cosmetic?)
Does a top dress make sense?
Recent rain in some regions could improve yield targets. Before investing in a nutrient top-up, assess whether the return justifies the cost. Try the tissue/soil tests described here: three low-cost tests. If you choose to apply, leave a test strip to assess if there was a yield benefit at harvest.
The optimal timing for additional nitrogen is before the 4- to 6-leaf stage.
(Tips on how to apply nitrogen and sulphur in-season)
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