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Herbicides and Rain

We’re looking at about 7″ across the county from the storm on Saturday. From a herbicide standpoint, the biggest questions are runoff and leaching. If the soil was physically moved around or away from the field then it’s safe to say the herbicides moved with it. If this is the case then residual herbicide activity will be reduced. Leaching is a little more complicated. The Leachability of herbicides depends upon water solubility and soil absorption. Dr. Prostko has a handy chart to see the water solubility and soil absorption of several common herbicides. Generally, herbicides with higher water solubility and lower soil adsorption characteristics are more likely to leach from the soil profile. You can see that dicamba has a very high water solubility and very low soil adsorption so it is very prone to leaching. Another example is Prowl. Prowl is not very soluble in water and is strongly adsorbed to soils. Thus, it is less likely to leach in comparison to other herbicides so it should still be around in most situations.

Trade NameCommon NameWater Solubility (ppm)Soil Adsorption (Koc)
Aatrexatrazine33100
Callistomesotrione220014-390
Dual Magnums-metolachlor488200
Engenia/Xtendimaxdicamba45002
Gramoxoneparaquat620,0001,000,000
Impacttopramezone0.6922-172
Laudistembotrione28.366
Libertyglufosinate1,370,000100
Prowlpendimethalin0.27517,200
Reflexfomesafen5060
Roundup (IPA Salt)glyphosate900,00024,000
Sonalanethalfluralin0.35,000
Tricormetribuzin110060
Valorflumioxazin1.79557
Ziduapyroxasulfone3.4957-114