Herbicide-resistant waterhemp continues to spread and is problematic for many North Dakota
soybean farmers. Herbicide-resistant Palmer amaranth continues to be introduced into new areas
in the state and will need to be controlled in soybean fields. Enlist E3 and Xtendflex soybean
offer the ability to use glufosinate and either 2,4-D or dicamba postemergence to control
glyphosate-resistant pigweeds. Commercially, there are escapes of waterhemp after an initial
glufosinate 2,4-D, or dicamba application each year for various reasons, such as environmental
conditions, or high weed density. Subsequent respray applications are typically used in these
situations to control weed escapes. This project will evaluate the optimal order of application of
glufosinate and 2,4-D, or glufosinate and dicamba, as well as the optimal respray interval for
control of glyphosate-resistant waterhemp and Palmer amaranth following initial application.

1) Determine the optimal respray interval for glufosinate, 2,4-D, and dicamba, followed by
either glufosinate, 2,4-D, or dicamba applied at intervals of 7, 14, or 21 days after initial
application.
2) Determine the optimal order of application for glufosinate and 2,4-D (i.e. E3 soybean)
and glufosinate and dicamba (i.e. Xtendflex soybean).

-Manuscript submitted to a scientific journal (after a second year of research).
-Results will be shared at Extension meetings and Scientific meetings.
-Trials will be on display at Weed Science Field Days that are open to the public.

Updated January 5, 2024:
FY 2024 Mid-Year Report ND Soybean Council
Optimal Respray Intervals for Glufosinate, 2,4-D, and Dicamba on Glyphosate-Resistant Waterhemp and Palmer amaranth (Year 2).
Objectives of the research:

1) Determine the optimal respray interval for glufosinate, 2,4-D, and dicamba, followed by
either glufosinate. 2,4-D, or dicamba applied at intervals of 7, 14. or 21 days after initial
application.
2) Determine the optimal order of application for glufosinate and 2,4-D (i.e. E3 soybean)
and glufosinate and dicamba (i.e. Xtendflex soybean).


Completed work:
Field trials were completed on waterhemp at NDSU’s Northwest 22 site and a Palmer amaranth research site in Barnes county, ND. Soybean were planted on May 21 and June 12, at NW22 and Barnes county, respectively.

The first postemergence application in both trials at NW22 was applied on June 12 2023, with sequential applications on June 19, July 3, and July 10.

The first postemergence application in both trials at Barnes county was applied on July 5 2023, with sequential applications on July 12, July 19, and July 26.

Plots were visibly evaluated for waterhemp control on a 0 to 100 % scale (0 representing no injury, and 100 representing complete plant death). Waterhemp and Palmer amaranth density and biomass were collected at 28 days following the last application. Initial analysis conducted as RCBD with treatment separation using Fisher’s LSD at P<0.05.


Preliminary results:


Enlist trial with waterhemp
Treatment Final waterhemp control (%) Final waterhemp density (plants m-2) Final waterhemp biomass (g m-2)
Enlist One fb Enlist One 7 DAT 95 AB 0 B 0 B
Enlist One fb Enlist One 14 DAT 99 A 0 B 0 B
Enlist One fb Enlist One 21 DAT 95 AB 0 B 0 B
Enlist One fb Liberty 7 DAT 98 A 0 B 0 B
Enlist One fb Liberty 14 DAT 96 AB 0 B 0 B
Enlist One fb Liberty 21 DAT 99 A 0 B 0 B
Liberty fb Enlist One 7 DAT 95 AB 1 B 2 B
Liberty fb Enlist One 14 DAT 94 AB 1 B 0 B
Liberty fb Enlist One 21 DAT 91 B 0 B 0 B
Liberty fb Liberty 7 DAT 91 B 1 B 1 B
Liberty fb Liberty 14 DAT 95 AB 0 B 0 B
Liberty fb Liberty 21 DAT 95 AB 1 B 2 B
Nontreated 0 C 23 A 154 A
Enlist One rate was 32 fl oz/A. Liberty rate was 32 fl oz/A. 8.5lb per 100 gallons of AMS was used for all treatments.
DAT; days after initial treatment. fb; followed by.
Different letters within same column represent statistical separation at P<0.05


Dicamba trial with waterhemp
Treatment Final waterhemp control (%) Final waterhemp density (plants m-2) Final waterhemp biomass (g m-2)
Engenia fb Engenia 7 DAT 82 BCD 17 B 6 BC
Engenia fb Engenia 14 DAT 83 ABCD 3 B 1 C
Engenia fb Engenia 21 DAT 70 D 8 B 2 C
Engenia fb Liberty 7 DAT 83 ABCD 10 B 3 C
Engenia fb Liberty 14 DAT 85 AB 2 B 1 C
Engenia fb Liberty 21 DAT 91 ABC 4 B 1 C
Liberty fb Engenia 7 DAT 79 CD 4 B 2 C
Liberty fb Engenia 14 DAT 81 BCD 7 B 2 C
Liberty fb Engenia 21 DAT 78 CD 5 B 26 B
Liberty fb Liberty 7 DAT 75 D 31 B 3 C
Liberty fb Liberty 14 DAT 93 AB 0 B 0 C
Liberty fb Liberty 21 DAT 96 A 0 B 0 C
Nontreated 0 E 240 A 98 A
Engenia rate was 12.8 fl oz/A. Liberty rate was 32 fl oz/A. NIS at 0.5% V/V used for Engenia. 8.5lb per 100 gallons of AMS was used for Liberty.
DAT; days after initial treatment
Different letters within same column represent statistical separation at P<0.05


Enlist trial with Palmer amaranth
Treatment Final Palmer amaranth control (%) Final Palmer amaranth density (plants m-2) Final Palmer amaranth biomass (g m-2)
Enlist One fb Enlist One 7 DAT 93 A 0 B 0 B
Enlist One fb Enlist One 14 DAT 95 A 0 B 0 B
Enlist One fb Enlist One 21 DAT 94 A 0 B 0 B
Enlist One fb Liberty 7 DAT 79 BC 1 B 1 B
Enlist One fb Liberty 14 DAT 90 AB 0 B 0 B
Enlist One fb Liberty 21 DAT 94 A 0 B 0 B
Liberty fb Enlist One 7 DAT 79 BC 1 B 2 B
Liberty fb Enlist One 14 DAT 90 AB 0 B 0 B
Liberty fb Enlist One 21 DAT 90 AB 1 B 4 B
Liberty fb Liberty 7 DAT 72 C 1 B 2 B
Liberty fb Liberty 14 DAT 92 A 2 B 3 B
Liberty fb Liberty 21 DAT 97 A 2 B 1 B
Nontreated 0 D 30 A 132 A
Enlist One rate was 32 fl oz/A. Liberty rate was 32 fl oz/A. 8.5lb per 100 gallons of AMS was used for all treatments.
DAT; days after initial treatment. fb; followed by.
Different letters within same column represent statistical separation at P<0.05

Dicamba trial with Palmer amaranth
Treatment Final Palmer amaranth control (%) Final Palmer amaranth density (plants m-2) Final Palmer amaranth biomass (g m-2)
Engenia fb Engenia 7 DAT 80 ABC 2 BC 28 BCD
Engenia fb Engenia 14 DAT 85 AB 2 BC 13 BCD
Engenia fb Engenia 21 DAT 83 ABCD 1 C 2 CD
Engenia fb Liberty 7 DAT 68 CD 5 BC 27 BCD
Engenia fb Liberty 14 DAT 76 ABCD 6 BC 25 BCD
Engenia fb Liberty 21 DAT 90 A 1 C 1 D
Liberty fb Engenia 7 DAT 70 BCD 5 BC 32 BC
Liberty fb Engenia 14 DAT 73 BCD 3 BC 5 CD
Liberty fb Engenia 21 DAT 91 A 1 C 1 D
Liberty fb Liberty 7 DAT 60 D 8 B 36 B
Liberty fb Liberty 14 DAT 78 ABC 1 C 3 CD
Liberty fb Liberty 21 DAT 91 A 5 BC 4 CD
Nontreated 0 E 24 A 219 A
Engenia rate was 12.8 fl oz/A. Liberty rate was 32 fl oz/A. NIS at 0.5% V/V used for Engenia. 8.5lb per 100 gallons of AMS was used for Liberty.
DAT; days after initial treatment
Different letters within same column represent statistical separation at P<0.05

Work to be completed:
• Data will be further analyzed for factorial effects of herbicide sequence and respray timing across all treatments. Data from 2022 and 2023 will be combined for analysis where appropriate.
• Final data will be presented throughout the winter meeting season, including the Getting it Right in Soybean meeting, and at the

View uploaded report

This project will evaluate the optimal herbicide sequence and respray intervals for control of
waterhemp and Palmer amaranth in E3 and Xtendflex soybean. Results should help guide the
best time to scout for pigweed escapes from postemergence applications and the best time to
apply a follow-up treatment. The results should also help determine if 2,4-D or dicamba is more
efficacious on waterhemp and Palmer amaranth to help guide soybean technology planting
decisions on acres where either weed is the driver weed species. All of these results will be
important to help reduce the amount of seed production and risk for development of herbicide
resistance in order to prolong the amount of time that these soybean technologies are useful for
controlling herbicide-resistant pigweeds.