Perennial weed control is best achieved with preharvest applications of glyphosate. Once again, planning your rotation will give you the opportunity to control these tough perennials in the crop so harvest and weed staging work together. Many farmers do not like to use preharvest in canola because they feel the damage from the sprayer is more than acceptable. Pulses should be a good candidate for preharvest as the Roundup will also help dry down the crop for harvest. The problem in pulse crops is that when you have high thistle populations, the pulses are not competitive and where the thistles are, you have no crop at all.
Many farmers like to control the perennial weeds before they plant their pulse crops.
That leaves cereal crops for the preharvest application. But if you are trying for malt barley the maltsters don't want glyphosate residues on the barley. Therefore, preharvest should be used on the other cereal crops and flax. An additional benefit to spraying Roundup on flax is that it stops the flax from continuing to grow and thereby saves moisture for the next year's crop. If Preharvest Roundup is applied to the cereal crop in year 4 for perennial weed control, you can then assess the control in the oilseed crop in year 1 of the chart.