Why should soil herbicides not be applied to frozen soils?

• A. They may not be absorbed by the soil when frozen, reducing effectiveness.
• B. They evaporate quickly on frozen soils.
• C. They become more effective on frozen soils.
• D. They are completely safe on frozen soils.

Answer: (C)

Soil-applied herbicides rely on liquid soil water to dissolve, move through the soil, and reach weed seeds or roots. When the soil is frozen, there is little to no free liquid water in the pore spaces because water is locked as ice. This greatly slows or prevents the herbicide from being absorbed into the soil and distributed to the weed targets. As a result, the herbicide tends to stay on or near the surface and doesn’t reach the root zone effectively, leading to poor weed control. There’s also a risk that the chemical could be unevenly redistributed or stay inactive until thaw, further reducing effectiveness.

The suggestion that they become more effective on frozen soils isn’t supported by how these products work, and they aren’t guaranteed safe or harmless on frozen soils either. Evaporation isn’t the primary issue with frozen soils, and the main concern is the lack of mobility and activation in frozen conditions. Delay application until soils are unfrozen and adequately moist, or follow labeled guidance for weather-appropriate use.