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
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

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
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.
^ea priori orthogonal contrasts; ** = significant (P

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
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.
^da priori orthogonal contrasts; ** = significant (P

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