None of us need reminding how difficult 2021 was for farming in Western Canada because of the severe drought experienced in most places, along with the disruptions of a global pandemic. If it were possible, I would have asked my high school bully if that offer to slap me into next year was still on the table! But at last, here we are in 2022, looking forward to a much better year. However, like a boxer ready to step back into the ring, we may still be carrying a few scars from our last fight. One of those scars could be herbicide carryover.
What is herbicide carryover?
Herbicide carryover happens when a soil residual herbicide does not break down completely over the summer and leaves residues that may harm the next crop. Herbicides break down more quickly in warm, moist soils due to increased microbial and chemical degradation under those conditions. Therefore, the extremely dry conditions experienced in many areas during last year’s growing season have increased the potential for crop damage from herbicide carryover in 2022. In general, areas that received less than 125 millimeters (about 5 inches) of accumulated rainfall between June 1 and August 30 may be at risk, especially if the soils are sandy, have low organic matter, and soil pH is lower than 6.5 or higher than 7.5.
How to detect herbicide carryover before the start of the cropping season
A simple way to assess suspected herbicide carryover is to do a bioassay. This involves growing the intended crop or a sensitive crop in pots containing soil from a treated field and a ‘’check” soil from an untreated area close to the field. Seeds should be planted not later than a day or two after the soils are collected to minimize herbicide degradation of the soil samples under favourable conditions, which will skew the results. Place the pots in direct sunlight or under a suitable light source, at about room temperature. Water as needed but avoid waterlogging. Observe the plants 2 – 3 weeks after emergence and note any visual differences in plant height, root density, and overall plant health. Plants experiencing herbicide injury will show symptoms of poor health when compared to the check.
How to manage herbicide carryover
Accurate record-keeping that indicates the type of herbicides and amount of rainfall a field received is important to assess potential herbicide carryover risks. Pay attention to rotational restrictions by the herbicide manufacturer and consult with the manufacturer for additional guidance in abnormal situations such as after the drought of 2021. If herbicide carryover is confirmed, the safe thing to do would be to seed the field to a crop with tolerance to the herbicide group that has been carried over, taking other essential farm management plans into consideration. Your SynergyAG team will be happy to provide the necessary agronomic guidance for a successful 2022 season.
– Ikenna Mbakwe, PhD, PAg
Head of Research