Early-season Weed Control in Roundup Ready 2 Xtend® Soybean
Starting weed-free at planting is important for season-long weed control and maximum yield potential.
Most kochia emerges in early spring with subsequent smaller flushes throughout the growing season, while Palmer amaranth emerges later in the year for an extended period of time.
When environmental conditions are challenging for weed control prior to planting, failure of burndown control of kochia can occur, which could result in kochia present at planting time.
The objective of this study was to determine the best strategy for managing kochia that escaped a burndown herbicide treatment in soybean with planting-time and early post-emergence applications
Research Site Details
The trial was arranged in a randomized complete block design with three replications.
Kochia was treated with a blanket application of 4 fl oz of XtendiMax® herbicide with VaporGrip® Technology (approximately 1/5 the labelled application rate) two weeks prior to planting to simulate a lack of control scenario.
Kochia was approximately 3-6 inches in height at the pre-application timing (PRE).
Early post-emergence applications (POST) were applied at the V2 growth stage. At this time, kochia was approximately 9-12 inches in height and Palmer amaranth was approximately 4 inches in height.
Rainfall one day after the POST application (Table 1) resulted in a new flush of Palmer amaranth.
Some volunteer corn was present in the trial (Figure 5, 7, and 8).
Understanding the Results
At 21 days after the PRE treatment, kochia and Palmer amaranth control was significantly greater in plots that received a treatment with XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide + a residual herbicide (Treatments 2, 3, and 4) compared to XtendiMax® with VaporGrip® Technology + Roundup PowerMAX® herbicide alone, indicating that Tricor® 4F and Valor® SX contributed to better control of kochia (Figure 1).
Kochia control was significantly greater when using XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide compared to paraquat or parquat + metribuzin (Treatments 5 and 6) at 48 days after the PRE treatment (Figure 2).
The highest level of Palmer amaranth control at 48 days after the PRE treatment resulted from XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide + either Valor® SX or Warrant® Herbicide + Tricor® 4F (Treatments 2 and 4) (Figure 2).
Including Warrant® Herbicide or Warrant® Ultra Herbicide with XtendiMax® herbicide with VaporGrip® Technology + Roundup PowerMAX® herbicide in the POST treatment (Treatments 8 and 9) resulted in a significant increase in Palmer amaranth control 21 days after the POST application (Figure 2).
What Does This Mean for Your Farm?
Starting clean with an effective burndown herbicide and including a residual herbicide at planting resulted in the best control of kochia and Palmer amaranth.
Including a residual herbicide in post-emergence applications significantly improved Palmer amaranth control.
Delaying the herbicide application until the V2 growth stage resulted in applications to large kochia plants and a dense canopy of Palmer amaranth plants, which reduces the effectiveness of post-emergence herbicides.