Effects of flooding and wet conditions on weed management

Wet weather and flooding can affect weeds and weed control: 

  • Wet weather conditions can be stressful and may impact the growth and vigor of crops; this, in turn, can affect crop-weed competitive interactions.
  • Wet soils can result in delayed or missed weed control events, such as cultivation and spraying. This may allow weeds to escape optimum management windows.
  • Driving on or physically working wet soils can lead to compaction. Compaction can affect soil aeration, crop root system development, and future drainage in the field.
  • Weeds that are stressed by wet weather conditions may not respond well to postemergence herbicides. Rain events may be associated with fluctuations in soil and air temperature, which can also affect weed vigor and, subsequently, herbicide performance.
  • If trying to make postemergence applications between rainfall events, check the product label for rainfast periods.
  • Too much rainfall could facilitate the leaching of residual herbicides that have high water solubility (measured in ppm) and low soil adsorption (measured in Koc). Herbicide loss may be more pronounced on sandy/corase soils. For herbicides that do bind tightly to soil, microbial degradation may be altered under wet conditions.
  • Wet conditions could increase the injury to crops by residual herbicides if crop emergence is slowed.
  • Flooding may physically move herbicide-treated soil via erosion. This may result in chemicals moving out of a field and onto non-target plants or becoming concentrated in low spots within a planting area. Both conditions can result in reduced weed control (or evenness of weed control) and increase injury potential to desirable species or crop plants.
  • Flooding may result in weed seed movement.
  • If weed control has failed, applicators may feel compelled to act rapidly to manage unwanted vegetation. Don’t let haste lead to herbicide drift events.