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Knock Out Soybean Weeds Before They Reach 4 Inches

This chart compares the height of a weed against a cell phone.Caption: Control weeds in your soybean fields before they reach 4 inches – a height even shorter than most cell phones.

Weeds like waterhemp and Palmer amaranth can grow up to 1 inch per day. This rapid growth rate makes post-emergence herbicide application timing crucial. If you spray a weed taller than 4 inches, it’s more likely to survive the herbicide application and continue growing. This leads to resistance to that herbicide and/or its active ingredients.


The University of Minnesota Extension says post-emergence herbicides are most effective when applied to small weeds that are actively growing. Application to larger weeds may result in poor weed control and increased crop injury. Virginia Tech University says to spray before weeds reach 4 inches in height because dealing with larger weeds will accelerate the development of herbicide resistance, resulting in less weed control and decreased yield potential.

Applying a post-emergence herbicide, such as Flexstar® GT 3.5, before weeds can hit 4 inches can help preserve the efficacy of the herbicide application and reduce the chance of resistance building to the active ingredients.

Visit www.ResistanceFighter.com to learn more about how to combat difficult weeds and prevent herbicide resistance from developing.

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