Keep this year's crop protection from hurting next year's yields
Knowing your field's herbicide carryover risk can improve your use of soil applied herbicide
Whether or not herbicide persistence will be an issue for next year's crop is largely influenced by soil properties. The soil characteristics that contribute to a herbicide degrading or remaining are:
Soil Texture: soils high in clay have a greater potential for carryover because of increased binding of the herbicide to soil particles along with reduced loss of the herbicide to leaching or through volatilization. This allows the herbicide to remain in the soil longer so that is around to injure following crops.
Organic Matter: similar to medium and fine-textured soils, the ability of soil OM to hold herbicides causes the carryover risk to increase as soil OM increases.
Soil pH: both high and low soil pH influences the carryover risk and the immediate effectiveness of different herbicide families. High pH soils slow the degradation of certain herbicides by reducing the chemical and microbial breakdown of the herbicide. Additionally, as pH increases, lesser amounts of certain herbicides are held by the soil and more likely to be taken up by plants. This means the herbicide can remain in the soil longer but still be available to injure future crops. In low pH soils, some herbicides can be tightly but temporarily bound to the soil making them less effective at weed control but later available for plant uptake on sensitive follow crops.
Knowing where and how great your carryover risk is allows for improved decision making around which herbicide to use and at what rate. Targeted scouting and soil sampling for laboratory bioassay and chemical analysis can quantify the residual herbicide.
Be sure to check the product label to see just how your particular herbicide will interact with the soil. The chemical makeup of each herbicide family determines how it will react to these soil properties along with weather conditions, which also significantly influences the likelihood of a herbicide causing problems in next year's crop.
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