Over-reliance on glyphosate as the primary method of weed control has clearly pushed the selection of glyphosate-resistant weeds. In Nebraska, we have confirmed glyphosate-resistant populations of common ragweed, common waterhemp, giant ragweed, marestail, kochia, and Palmer amaranth.
With glyphosate no longer an option for the control of these glyphosate-resistant populations, growers are looking for herbicides with different modes of action. A diversified herbicide program for weed management needs to be used to avoid evolving resistance to multiple modes of action.
A diversified herbicide program should include at least two effective modes of action in each application and should rotate modes of action between years to keep selection pressure low.

A field study was conducted in 2015 and 2016 near Adams to evaluate herbicide programs for the control of glyphosate-resistant common ragweed in LibertyLink (glufosinate-resistant) soybean. Adams was where glyphosate-resistant common ragweed was first confirmed in the state.
Glyphosate-resistant common ragweed can be controlled effectively by using a diversified preplant and POST herbicide program in LibertyLink soybean.
Remember This: Common Ragweed Gets An Early Start
Common ragweed has an early spring emergence period in Nebraska with 90% total emergence reached before mid-May. This necessitates using a preplant burndown herbicide to control emerged common ragweed before planting (Figure 1).
- Herbicide options such as 2,4-D, Authority First, Optill plus Outlook, paraquat, Sharpen plus 2,4-D, or Valor XLT effectively controlled common ragweed before planting and up to three weeks after application (Figure 2).
- Liberty applied post-emergence alone or in a tank-mixture with Prefix, Pursuit, or Warrant controlled 84%-98% glyphosate-resistant common ragweed (Figure 3).
- For best control and to reduce the evolution of herbicide resistance no single mode of action should be used preplant or post-emergence.
- Single applications (only preplant or only POST) resulted in less weed control, greater weed biomass, and less soybean yield.
- Three applications (preplant, pre-emergence, late post-emergence or preplant, early post-emergence, late post-emergence) did not result in greater common ragweed control, weed biomass reduction, or soybean yield (Figure 4 and 5).
The cost of preplant followed by post-emergence herbicide programs ranged from $59.17 to $93.09 per acre with application and provided the highest gross profit margins compared to no weed control and single- or triple-application herbicide programs (Table 1).
- Single application herbicide programs were cheapest but resulted in much less profit due to low soybean yield.
The pre-plant/pre-emergence/post-emergence program provided equal control of glyphosate-resistant common ragweed as the pre-plant/early-post/late-post-emergence program.
HERBICIDE PROGRAM | PROGRAM COST A | GROSS REVENUE B,C | GROSS PROFIT MARGIN D |
---|---|---|---|
————– $/acre ————— | |||
Preplant: Optill [2 oz/acre] + Outlook [21 fl oz/acre ] | 79.88 | 284.64 | 204.76 |
Post-emergence: Liberty [36 fl oz/acre] | |||
Preplant: Authority First [6.4 oz/acre] | 72.93 | 253.51 | 180.58 |
Post-emergence: Liberty [36 fl oz/acre] | |||
Preplant: Valor XLT [5 oz/acre] | 68.12 | 250.21 | 182.09 |
Post-emergence: Liberty [36 fl oz/acre] | |||
Preplant: 2,4-D [2.1 pt/acre] | 59.17 | 250.48 | 191.31 |
Post-emergence: Liberty [36 fl oz/acre] + [Pursuit 4 oz/acre] | |||
Preplant: Gramoxone Inteon [4 pt/acre] | 71.35 | 245.2 | 173.85 |
Post-emergence: Liberty [36 fl oz/acre] + Classic [0.75 oz/acre] | |||
+ Warrant [2 qt/acre] | |||
Preplant: Sharpen + 2,4-D (preplant) | 93.09 | 278.96 | 185.87 |
Post-emergence: Liberty [36 fl oz/acre] + Warrant [2 qt/acre] | |||
Preplant: Valor XLT (preplant) | 104.36 | 264.19 | 159.83 |
Early post-emergence: Liberty [29 fl oz/acre] + Prefix [2 pt/acre] | |||
Late post-emergence: Liberty [29 fl oz/acre] + Warrant [1.5 qt/acre] | |||
Preplant: 2,4-D [2.1 pt/acre] | 81.04 | 271.71 | 190.67 |
Pre-emergence: Authority MTZ [18 oz/acre] | |||
Post-emergence: Liberty [36 fl oz/acre] | |||
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A Required herbicide adjuvants and application cost ($7.33 per application) were included in program cost. B The average dryland soybean yield was 30 bu per acre for above herbicide programs in 2015 and 2016. C An average soybean price of $8.87 per bushel was used to calculate gross revenue. D Gross profit margin was calculated as gross revenue-program cost. |