By Sergio Cabello Leiva
Pre-emergence herbicides are not optional in Minnesota soybeans. They are the foundation of a working program. If you skip them or cut them back, you will fight weeds all season, especially resistant ones like waterhemp.
Start clean and stay ahead
Soybeans do not compete well early in the season. If weeds come up with the crop, the yield is already at risk before we consider a POST herbicide application (in most cases). A strong PRE herbicide keeps fields clean during those first critical weeks and gives you flexibility on your POST timing. This is even more important with early planting. When beans go in early, there is a longer gap before POST. That also means more competition from early emerging weeds, so residual herbicide selection becomes more critical.
Know what your herbicides do
Group 14 herbicides like Valor and Authority are strong on small broadleaf weeds and give you a quick start. They help control early flushes but do not last as long.
Group 15 herbicides such as Zidua and Dual II Magnum provide longer residual control and are highly effective against small-seeded weeds such as waterhemp and lambsquarter. These herbicides are the backbone of most programs.
But there are limits. Group 15 herbicides are largely ineffective against giant ragweed. In early-planted soybean fields with ragweed pressure, relying solely on Group 15 is a mistake. Residual programs need to specifically target that species. Premixes that include additional modes of action, especially Group 2 herbicides such as imazethapyr, chlorimuron or cloransulam provide more reliable control. Products that combine multiple residuals offer a broader spectrum and help manage resistance.
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