Frequent rainfall events throughout most of May in Nebraska have caused a significant delay in soybean planting compared to the five-year average (National Agricultural Statistics Service). USDA estimates that by June 2, 81% of soybeans had been planted in Nebraska, compared to 99% last year. The cool weather and wet soil conditions have disrupt the normal sequence of early season field operations such as herbicide applications. Many soybean fields in Nebraska have been planted this year without receiving preplant and/or preemergence herbicides.
Early season weed control is imperative to maximize soybean yield. Due to wet soil conditions, many soybean growers were not able to apply residual herbicides prior to soybean emergence. A few residual herbicides such as Dual II Magnum, FirstRate, Outlook, Prefix, Intrro, Pursuit, Warrant, and Zidua can be applied after soybean emergence. Some of these herbicides such as FirstRate (only for broadleaf weeds), Pursuit, and Prefix have foliar activity to control small, emerged weeds.
Given most soybeans grown in Nebraska are glyphosate-resistant, glyphosate (Roundup) can be tank-mixed with residual herbicides such as Dual II Magnum, Warrant, or Zidua (herbicides with no foliar activity) to control weeds already emerged at the time of application. It is also possible to tank-mix some other postemergence herbicides such as Cadet, Classic, Cobra, Flexstar GT, Fusion, Fusilade DX, Phoenix, and Ultra Blazer to control emerged weeds. This would add a different mode of action and might effectively delay or control glyphosate-resistant weeds. Tank-mix partners may cause other effects regardless of the application timing. Follow application timing and other restrictions of tank-mix herbicide partners as noted in the herbicide label.
Treatment Guide
Several important factors should be considered when addressing weed control with residual herbicides applied after soybean emergence:
- crop stage,
- tank mix partner, weed height,
- and carrier options.

Figure 1. Soybeans in early June in a field near Clay Center. (Photos by Amit Jhala)