Heavy rains the past week have put a lot of canola under pools of water. This water stress can make canola more susceptible to herbicide damage. Stress in the canola plants can lead to slower metabolism of the system herbicide, and plants are set back. In areas under extreme stress this year, damage appears to be enough to kill plants where sprayer booms overlap, in some cases.
When weeds are large, resist the temptation to increase herbicide rates if the crop is under stress.
Water stressed canola may also turn yellow because roots starved for oxygen can’t take up nutrients. Nutrient may be present at sufficient amounts, but the crop can’t utilize it.
If considering a nutrient top up to rescue the crop, wait until the ground dries up and roots can get working again before making that investment. Topdressing fertilizer may help when new green leaves start growing and when good growing conditions return.
Sulphur in the form of ammonium sulphate can provide an economic return when applied up to the bolting stage. Nitrogen applied past the 6-leaf stage is unlikely to provide an economic benefit.