February 18, 2019
- The use of residual herbicides in pre- and post-emergence programs is essential for managing weed species with extended emergence patterns, such as Palmer amaranth.
- The objective of this study was to compare weed control and yield from different pre- and post-emergence herbicide programs in Roundup Ready 2 Xtend® soybeans.
Research Site Details
- The trial was arranged in a randomized complete block design with four replications.
- The different herbicide treatments compared in this trial are listed in Table 1.
- Kochia emerged at planting, so kochia control assessments reflect both the foliar efficacy of the treatments in addition to residual control of kochia that emerged after planting and herbicide application (PRE- and POSTemergence).
- Palmer amaranth and kochia pressure was extremely high and both species are glyphosate-resistant at this site (Figure 1).
- Post-emergence treatments were applied at the V3 soybean growth stage when weeds were approximately four inches in height.
Understanding the Results
- No significant differences were observed in weed control but numerical differences were observed (Figure 2).
- The addition of XtendiMax® herbicide with VaporGrip® Technology with Warrant® Herbicide in the pre-emergence application (Treatment 10) resulted in improved Palmer amaranth and kochia control at the end of the season compared to Warrant® Herbicide alone (Treatment 1).
- Treatments containing Fierce® + Tricor® 4F followed by XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide + Warrant® Ultra Herbicide (Treatment 4) or Warrant® Herbicide (Treatment 7) resulted in numerically higher levels of kochia and Palmer amaranth control compared to the other treatments (Figure 2 and 4).
- Including Warrant® Ultra Herbicide (Group 14 + 15 herbicide) with XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide in the POST application provides an additional site of action on emerged weeds and weeds that have not yet emerged compared to Warrant® Herbicide (Group 15 herbicide).
- No significant differences in yield were observed between the different treatments (Figure 3).
What Does This Mean for Your Farm?
- Excellent control of Palmer amaranth and kochia can be obtained by combining multiple effective sites of action in both the pre- and post-emergence herbicide applications.
- Strong pre-emergence programs followed by a timely application of XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide + Warrant® Herbicide or Warrant® Ultra Herbicide resulted in numerically higher levels of weed control.
- Dicamba is a valuable tool for both pre- and post-emergence weed control in soybean, but additional residual preemergence herbicides are still needed.