Palmer Amaranth and Velvetleaf Control in Conventional Soybean Using Overlapping Residual Herbicide Programs

Palmer amaranth
Palmer amaranth in conventional soybean field is difficult to control (Photo by Amit Jhala).

Palmer Amaranth and Velvetleaf Control in Conventional Soybean Using Overlapping Residual Herbicide Programs

The cost of soybean seed has been increasing over the years, with herbicide-resistant soybean seed cost being higher than that of conventional soybean for having a technology fee. With the depressed corn and soybean prices in recent years in the United States, growers have shown interest in conventional soybean for better after-harvest incentives. A survey conducted in Nebraska in 2015 ranked Palmer amaranth and velvetleaf among the top six most problematic weeds in Nebraska (Sarangi and Jhala 2018). In Nebraska, Palmer amaranth biotypes resistant to acetolactate synthase (ALS)-, hydroxyphenylpyruvate dioxygenase (HPPD)-, photosystem (PS) II-inhibitors, and glyphosate have been confirmed.

Weed management in no-till conventional soybean is mostly herbicide-dependent; therefore, herbicide programs should be selected carefully that provide season-long weed control and high soybean yield. Unlike Roundup Ready- or LibertyLink soybean systems, there are few “rescue” POST herbicides available in conventional soybean, meaning that a pre-emergence (PRE) herbicide application is even more critical.

Field experiments were conducted in 2016 and 2017 at South Central Ag Lab, Clay Center, NE. Pre-emergence (PRE) and PRE followed by (fb) post-emergence (POST) herbicides, and PRE fb POST herbicide with residual (POST-WR) product tank-mixed were evaluated. Herbicides applied PRE including Trivence, Optil PRO, Valor XLT, Fierce, and Authority MTZ provided 95% to 100% control of Palmer amaranth and velvetleaf at 14 and 28 days after application (Table 1). Due to decline in the residual activities of the PRE soil-applied herbicides, PRE-only programs resulted in 66% control of Palmer amaranth at 28 DAPOST compared with 86% control for PRE fb POST programs (Table 2). Most of the PRE fb POST-WR programs resulted in greater than 97% control of Palmer amaranth at 28 DAPOST (Table 2). The PRE fb POST herbicide programs substantially improved velvetleaf control (98%) over the PRE-only herbicide programs (89% control) at 14 DAPOST (Table 3).

Table 1
Palmer amaranth and velvetleaf control as affected by PRE herbicide in conventional soybean in field experiments conducted in 2016 and 2017 in Nebraska.a,b
Palmer amaranth controlc Velvetleaf controlc
Herbicide trade name Herbicide active ingredient 14 DAPRE 28 DAPRE 14 DAPRE 28 DAPRE
--%-- --%--
Trivence Chlorimuron-ethyl/flumioxazin/metribuzin 99 a 97 a 98 a 96 a
Optill PRO Saflufenacil/imazethapyr + dimethenamid-P 100 a 98 a 99 a 97 a
Valor XLT Flumioxazin/chlorimuron-ethyl 100 a 98 a 98 a 97 a
Fierce Flumioxazin/pyroxasulfone 100 a 98 a 98 a 98 a
Authority MTZ Sulfentrazone/metribuzin 100 a 98 a 97 a 95 a
P-value 0.7 0.09 0.06 0.13

a Abbreviation: DAPRE, days after pre-emergence herbicide application.
b Data presented in this table were pooled across both years (2016 and 2017).
c Data were arc-sine square-root transformed before analysis; however, back-transformed original mean values are presented based on the interpretation of the transformed data, and the weed control data for the nontreated control plots were not included in the analysis.
d Means presented within each column with no common letter(s) are significantly different according to Fisher’s protected LSD where α = 0.05.

Table 2
Palmer amaranth control, density, and aboveground biomass reduction as affected by herbicide programs in no-tillage conventional soybean in field experiments conducted in 2016 and 2017 in Nebraska.a,b
Herbicide program Palmer amaranth controlc,d Densityd Biomass reductionc,d
Pre-emergence herbicide Post-emergence herbicide 14 DAPOST 28 DAPOST At harvest 28 DAPOST 56 DAPOST
--%-- # pl m-2 --%--
Nontreated control 0 0 0 110 a 0
Trivence _____ 76 cd 67 ef 42 ef 37 b 68 e
Marvel 97 a 90 cd 85 bc 10 d 89 cd
Marvel + Warrant 99 a 97 ab 95 ab 2 d 98 a
Optil PRO _____ 77 bcd 61 ef 28 fg 42 b 56 e
Cobra 99 a 91 c 81 cd 8 d 90 bcd
Cobra + Zidua 99 a 99 a 97 a 1 d 100 a
Valor XLT _____ 71 d 61 ef 36 efg 38 b 58 e
Ultra Blazer 98 a 88 cd 83 c 9 d 86 d
Ultra Blazer + Outlook 99 a 97 ab 90 abc 3 d 97 ab
Fierce _____ 87 b 83 d 67 d 16 cd 86 d
Cadet 96 a 92 c 80 cd 8 d 88 cd
Cadet + Prefix 99 a 99 a 97 a 1 d 98 a
Authority MTZ _____ 71 d 58 f 22 g 47 b 60 e
First Rate 83 bc 70 e 45 e 33 bc 68 e
First Rate + Anthem Maxx 97 a 94 bc 82 c 9 d 96 abc
P-value < 0.001 < 0.001 < 0.001 < 0.001 < 0.001
Contrastse
PRE-only vs. PRE fb POST 76 vs. 95** 66 vs. 86** 39 vs. 75** 36 vs. 14** 66 vs. 84**
PRE fb POST vs. PRE fb POST-WR 95 vs. 99* 86 vs. 97** 75 vs. 92** 14 vs. 3* 84 vs. 98**

a Abbreviation: DAPOST, days after post-emergence herbicide application; POST-WR, post-emergence herbicide with residual activity.
b Data presented in this table were pooled across both years (2016 and 2017).
c Data were arc-sine square-root transformed before analysis; however, back-transformed original mean values are presented based on the interpretation of the transformed data.
d Means presented within each column with no common letter(s) are significantly different according to Fisher’s protected LSD where α = 0.05.
e a priori orthogonal contrasts; ** = significant (P < 0.01) and * = significant (P < 0.05).

Table 3
Velvetleaf control and density as affected by herbicide programs in no-tillage conventional soybean in field experiments conducted in 2016 and 2017 Nebraska.a,b
Herbicide program Velvetleaf controlc,d Densityd
Pre-emergence Post-emergence herbicide 14 DAPOST 28 DAPOST 28 DAPOST
--%-- # plants m-2
Nontreated control 0 0 45 a
Trivence _____ 93 bc 92 abc 7 bc
Marvel 97 ab 94 abc 4 c
Marvel + Warrant 97 ab 97 ab 2 c
Optil PRO _____ 89 cd 88 bc 9 b
Cobra 99 a 96 ab 3 c
Cobra + Zidua 99 a 99 a 0 c
Valor XLT _____ 93 bc 93 abc 8 bc
Ultra Blazer 98 ab 94 abc 4 c
Ultra Blazer + Outlook 97 ab 97 ab 1 c
Fierce _____ 89 cd 85 c 10 b
Cadet 98 ab 95 abc 3 c
Cadet + Prefix 99 a 98 a 1 c
Authority MTZ _____ 79 d 67 d 15 b
First Rate 96 ab 91 bc 6 c
First Rate + Anthem Maxx 94 abc 94 abc 5 c
P-value < 0.001 < 0.001 < 0.001
Contrastse
PRE-only vs. PRE fb POST 89 vs. 98** 85 vs. 94** 10 vs. 4**
PRE fb POST vs. PRE fb POST-WR 98 vs. 97 NS 94 vs. 97 NS 4 vs. 2 NS

a Abbreviation: DAPOST, days after POST herbicide application; POST-WR, POST with residual.
b Data presented in this table were pooled across both years (2016 and 2017).
c Data were arc-sine square-root transformed before analysis; however, back-transformed original mean values are presented based on the interpretation of the transformed data.
d Means presented within each column with no common letter(s) are significantly different according to Fisher’s protected LSD where α = 0.05.
e a priori orthogonal contrasts; ** = significant (P < 0.01); NS, non-significant (P ≥ 0.05).

However, averaged across herbicide programs, velvetleaf control was similar in PRE fb POST-WR and PRE fb POST programs at 14 and 28 DAPOST. The year-by-treatment interaction was significant for soybean yield; therefore, yield data from 2016 and 2017 were presented separately. It is believed that the higher Palmer amaranth density in 2017 led to the lower soybean yield in all the treatments and nontreated control. Averaged across herbicide programs, PRE fb POST programs resulted in higher soybean yield compared to the PRE-only herbicide programs (Table 4). For more information read this article.

Table 4
Soybean yield affected by herbicide programs in conventional soybean in field experiments conducted in 2016 and 2017 in Nebraska.a
Herbicide program Soybean yieldb,c
PRE POST 2016 2017
Bushels per acre
Nontreated control 33 g 8 e
Trivence _____ 54 def 19 cd
Marvel 56 bcdef 26 bc
Marvel + Warrant 62 abc 42 a
Optil PRO _____ 50 f 17 d
Cobra 59 bcde 27 b
Cobra + Zidua 67 a 37 a
Valor XLT _____ 56 cdef 14 de
Ultra Blazer 59 bcde 25 bc
Ultra Blazer + Outlook 60 abcd 29 b
Fierce _____ 53 ef 25 bc
Cadet 57 bcdef 28 b
Cadet + Prefix 64 ab 40 a
Authority MTZ _____ 52 ef 14 de
First Rate 59 bcde 19 cd
First Rate + Anthem Maxx 58 bcdef 27 b
P-value < 0.001 < 0.001
Contrastsd
PRE-only vs. PRE fb POST 53 vs. 58** 18 vs. 25**
PRE fb POST vs. PRE fb POST-WR 58 vs. 62* 25 vs. 35**

a Abbreviation: DAPRE, days after PRE herbicide application; POST-WR, POST with residual.
b Means presented within each column with no common letter(s) are significantly different according to Fisher’s protected LSD where α = 0.05.
c Year-by-treatment interaction was significant for soybean yield; therefore, data from both years are presented separately.
d a priori orthogonal contrasts; ** = significant (P < 0.01), and * = significant (P < 0.05).

Reference: Sarangi D, Jhala AJ (2018) A statewide survey of stakeholders to access the problem weeds and weed management practices in Nebraska. Weed Technology 32:642-655