Once applied, herbicide active ingredients that land on the soil surface are broken down by soil microbes. Those microbes require moisture and warmth to chew through and neutralize the herbicide. When in-season water is limited, those active ingredients can stay in the soil, sometimes for years.
Cory Jacob, acting provincial weed specialist for the Saskatchewan Ministry of Agriculture, says there are limited soil testing options to determine how much herbicide residue is in soil. Saskatchewan has released carryover risk maps online that will help farmers gauge which fields could be an issue in 2024. (Scroll down for the map.)
Record keeping is key, Jacob says, as label re-cropping restrictions are based on a minimum amount of moisture in-season — and several areas of Saskatchewan have not received that required amount, perhaps in years.
Farmers who pick up new land should use an abundance of caution when considering cropping choices, especially if field records are limited.