Early season weed control in corn

Erin Burns<burnser5@msu.edu>, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences - April 30, 2020

Plan now for successful 2020 weed control in corn.

Uncontrolled weeds in a corn field. Photo by Erin Burns, MSU.

Given the difficult 2019 season and resulting weed seed production, weed populations could potentially be higher in 2020 compared to previous years. When considering weed control programs, keep in mind both the short range goal of controlling weeds so they are not yield limiting, and also the long range goal of weed seedbank depletion. Good control following seasons in which weed escapes were high will both preserve short term yield and have long lasting effects by diminishing the weed seedbank.

If you are in the process of making vital herbicide decisions for your corn acres, check out the Economics of Commercial Weed Control Programs in Corn from Michigan State University. Each year, the MSU weed science team asks herbicide companies to submit up to four weed control programs for the study based on soil type and weed infestation history. In 2019, 24 herbicide programs were evaluated (Table 1). Use Table 2 to compare how your current corn herbicide program fits into the broad spectrum of commercial programs available. Results in Table 2 include corn injury, weed control, program costs, corn yield and economic returns of the 24 herbicide programs evaluated.

Overall, 23 of the 24 herbicide programs tested resulted in greater than 90% control of all weeds prior to harvest. Twenty-three of the 24 herbicide programs resulted in statistically similar yield. The maximum yield in this trial was 233 bushels per acre, and yield was 83 bushels per acre in the untreated (weedy control) treatment. Weed competition in this trial resulted in a yield loss of 150 bushels per acre (64%). Twenty out of the 24 herbicide programs resulted in statistically similar gross margins. The maximum gross margin in this trial was $838.25 per acre, and the gross margin in the untreated weedy treatment was $311.91 per acre. Weed competition in this trial resulted in an economic loss of $526.34 per acre (63%).

In addition to the 2019 economics of commercial weed control programs in corn, you can also find results for soybean (non-GMO, convention till and no-till) dating back to 2004 on the MSU Weed Science website.

Further considerations

When designing herbicide programs to delay the evolution of and battle herbicide resistant weeds, the first step is to make sure your program utilizes multiple effective sites of action. The herbicide site of action refers to the location or enzyme where the herbicide acts to disrupt plant growth. Herbicide sites of action are numbered and can be found on the herbicide label or in the 2020 MSU Weed Control Guide for Field Crops. I took the treatment list for all herbicide entries in the corn commercial comparison trials from 2006-2019 and tallied the frequency of sites of action used (Table 3).

Overall site of action group numbers 5 (e.g. atrazine), 15 (e.g. Dual, Outlook, Harness) and 9 (e.g. glyphosate) were used most frequently overtime. Further, I took the treatment trade names for all herbicide entries in the corn commercial comparisons trials from 2006-2019 and created a word cloud, which is a visual representation of the treatments and highlights the frequency of the treatments included in the study overtime. When interpreting a word cloud, the treatments that are larger and are the same color were included more frequently in the corn commercial comparisons studies from 2006-2019 than those that are smaller. Not surprisingly, glyphosate (e.g., roundup) was the most frequent treatment followed by atrazine (Figure 1).

Word cloud of treatment trade names — Figure 1. Word cloud of treatments (trade names) included in MSU Economics of Commercial Weed Control Programs in Corn from 2006-2019. When interpreting a word cloud, the treatments that are larger and are the same color were included more frequently in the corn commercial comparisons studies form 2006-2019 than those that are smaller.

Table 1. Commercial corn herbicide programs evaluated in 2019.
Conventional	Treatments (Rate/A)	Abbreviated Form
PRE	Corvus (3.3 oz) + Harness Xtra (1.8 qt)	Corvus + HarnXtra
PRE	Acuron (3 qt)	Acuron
Roundup Ready
EPOS	Armezon PRO (16 oz) + Roundup PowerMax (16 oz) + Atrazine (1.1 lb) + NIS (0.25%) + AMS (8.5 lb)	Armezon PRO + RupPM + Atra
	Degree Xtra (2 qt) + Laudis (3 oz) + Roundup PowerMax (32 oz) + AMS (8.5 lb)	DegXtra + Laud + RupPM
	Capreno (3 oz) + Roundup PowerMax (22 oz) + Atrazine (1.1 lb) + AMS (8.5 lb)	Capreno + RupPM + Atra
	Anthem MAXX (4 oz) + Balance Flexx (3 oz) + Atrazine (2.2 lb) + Roundup PowerMax (22 oz) + AMS (8.5 lb)	AnthM + Bal Flexx + Atra + RupPM
	Warrant (3 pt) + Atrazine (0.55 lb) + Roundup PowerMax (22 oz) + AMS (8.5 lb)	Warrant + Atra + RupPM
	Harness Max (64 oz) + Atrazine (1.1 lb) + Roundup PowerMax (22 oz) + AMS (8.5 lb)	HarnMax + Atra + RupPM
	Halex GT (4 pt) + Atrazine (0.55 lb) + NIS (0.25%) + AMS (8.5 lb)	HalGT + Atra
PRE/POST	Zidua SC (3.2 oz) + Sharpen (2 oz) + Atrazine (1.1 lb) fb. Roundup PowerMax (32 oz) + AMS (8.5 lb)	Zidua SC + Sharp + Atra fb. RupPM
	Zidua SC (3.2 oz) + Atrazine (1.1 lb) fb. Roundup PowerMax (32 oz) + AMS (8.5 lb)	Zidua SC + Atra fb. RupPM
	Verdict (12 oz) + Atrazine (1.1 lb) fb. Roundup PowerMax (32 oz) + AMS (8.5 lb)	Verdict + Atra fb. RupPM
	Balance Flexx (4 oz) fb. DiFlexx Duo (24 oz) + Roundup PowerMax (22 oz) + AMS (8.5 lb)	Bal Flexx fb. DiFlexx Duo + RupPM
	SureStart II (3 pt) + Atrazine (1.65 lb) fb. Durango DMA (32 oz) + AMS (8.5 lb)	SureStart + Atra fb. Durango
	Resicore (1.25 qt) + Atrazine (1.1 lb) fb. Resicore (1.25 qt) + Durango DMA (32 oz) + AMS (8.5 lb)	Resi + Atra fb. Resi + Durango
	Resicore (2.5 qt) + Atrazine (1.1 lb) fb. Durango DMA (32 oz) + AMS (8.5 lb)	Resi + Atra fb. Durango
	Cinch ATZ (2.1 qt) fb. Realm Q (4 oz) + Atrazine (0.55 lb) + Durango DMA (32 oz) + AMS (8.5 lb)	Cinch fb. Realm Q + Durango
	Anthem MAXX (4 oz) + Balance Flexx (3 oz) + Atrazine (1.65 lb) fb. Status (4 oz) + Roundup PowerMax (22 oz) + AMS (8.5 lb)	AnthM + Bal Flexx + Atra fb. Stat + RupPM
	Degree Xtra (2 qt) fb. DiFlexx (8 oz) + Roundup PowerMax (22 oz) + AMS (8.5 lb)	DegXtra fb. DiFlexx + RupPM
	TripleFLEX II (1 qt) + Degree Xtra (1.5 qt) fb. Roundup PowerMax (22 oz) + AMS (8.5 lb)	TripleFLEX II + DegXtra fb. RupPM
	Acuron (1.5 qt) fb. Halex GT (3.6 pt) + Atrazine (0.55 lb) + NIS (0.25%) + AMS (8.5 lb)	Acuron fb. Halex GT + Atra
	Armezon PRO (16 oz) + Callisto (3 oz) + Atrazine (1.1 lb) fb. Roundup PowerMax (32 oz) + AMS (8.5 lb)	Armezon + Call + Atra fb. RupPM
	Bicep II Magnum (1.3 qt) fb. Halex GT (3.6 pt) + Atrazine (0.55 lb) + NIS (0.25%) + AMS (8.5 lb)	Bicep fb. Halex GT + Atra

Table 2. Corn injury, weed control, program costs, corn yield, and economic returns of 24 herbicide programs in 2019.
Programs	Herbicide Treatments⁵	Injury 10 DAP	ANGR	CHEAL	AMAPO	AMBEL	ABUTH	All Weeds	Cost¹	Yield	Economic Return²
Programs	Herbicide Treatments⁵	Injury 10 DAP	Prior to harvest (46 d after POST)					All Weeds	Cost¹	Yield	Economic Return²
Conventional		(%)	% Control					(≥ 90%)	($/A)	(bu/A)	($/A)
PRE	Corvus + HarnXtra	0	95.8	100	100	99.5	100	YES	54.89	222.8*³	780.52**⁴
PRE	Acuron	0	100	100	100	100	100	YES	61.25	210.5*	727.94
Roundup Ready
EPOS	Armezon PRO + RupPM + Atra	0	95.3	99.5	100	100	99.5	YES	35.88	233.1*	838.25**
	DegXtra + Laud + RupPM	0	99	100	100	100	100	YES	48.19	228.4*	808.31**
	Capreno + RupPM + Atra	0	95.3	100	100	99.5	100	YES	35.77	217.3*	779.2**
	AnthM + Bal Flexx + Atra + RupPM	0	100	100	100	100	100	YES	56.30	223.4*	781.45**
	Warrant + Atra + RupPM	0	90	100	100	92.5	97.5	YES	27.77	219.3*	794.51**
	HarnMax + Atra + RupPM	0	90.8	98.8	92.5	98.8	98.8	YES	50.70	221.8*	780.86**
	HalGT + Atra		92	100	100	99.5	100	YES	40.06	226.7*	810.16**
PRE/POST	Zidua SC + Sharp + Atra fb. RupPM	0	99	99.5	100	100	100	YES	56.10	217.3*	758.68**
	Zidua SC + Atra fb. RupPM	0	99	98.8	100	99	99.5	YES	43.47	210.9*	747.04
	Verdict + Atra fb. RupPM	0	96	99	97	99.5	99.5	YES	47.81	222.5*	786.47**
	Bal Flexx fb. DiFlexx Duo + RupPM	0	95.8	100	100	100	100	YES	55.54	224.6*	786.52**
	SureStart + Atra fb. Durango	0	90	100	100	99	100	YES	60.35	218.9*	760.53**
	Resi + Atra fb. Resi + Durango	0	100	100	100	100	100	YES	75.78	224.1*	770.94**
	Resi + Atra fb. Durango	0	97.3	100	100	100	100	YES	69.44	221.6*	761.75**
	Cinch fb. Realm Q + Durango	0	100	100	100	100	100	YES	64.66	223.6*	774.03**
	AnthM + Bal Flexx + Atra fb. Stat + RupPM	0	100	100	100	100	100	YES	63.95	228*	790.96**
	DegXtra fb. DiFlexx + RupPM	0	99.5	100	100	100	100	YES	54.30	218.3*	764.14**
	TripleFLEX II + DegXtra fb. RupPM	0	99.5	100	100	99.5	100	YES	56.76	219.7*	767.12**
	Acuron fb. Halex GT + Atra	0	100	100	100	100	100	YES	71.83	227.3*	780.55**
	Armezon + Call + Atra fb. RupPM	0	93.3	100	98.8	98.3	98.8	YES	55.84	210.4*	733.07
	Bicep fb. Halex GT + Atra	0	100	100	100	99.5	99.5	YES	58.36	230.5*	806.2**
	Untreated	0	0	0	0	0	0	NO	0	83.2	311.91
Abbreviations: ANGR = annual grasses, mainly foxtail species, CHEAL = common lambsquarters, AMAPO = Powell amaranth, AMBEL = common ragweed, ABUTH = velvetleaf, fb. = followed by ¹Herbicide costs = avg. of price lists; App. cost = $7.50/A; seeding rate = 34,600 seeds/A. Weed control costs = Herbicide $ + Additive $ + Application $ ²Crop selling price = $3.75/bu (December 2019). Economic return = (Yield x Price) – Weed Control Costs ³Not statistically different from the highest yielding ⁴*Not statistically different from the highest gross margins ⁵Many herbicide programs have long rotation restrictions to more sensitive crops, i.e., sugar beet, alfalfa, potatoes, etc. Consult Table 12 in the MSU Weed Control Guide for Field Crops (E-434) or the herbicide label for crop rotation restrictions.

Table 3. Frequency of herbicide sites of action (SOA) used in corn commercial comparisons studies from 2006-2019. Example herbicides for each site of action: 5 = atrazine, 15 = Dual, Outlook, Harness; 9 = glyphosate; 27 = Callisto, Balance Flexx, Armezon/Impact, Acuron, Laudis; 2 = Resolve, Accent Q; 4 = dicamba; 14 = Sharpen, Cadet; 10 = Liberty; 3 = Prowl H₂O; 19 = Status
SOA	Frequency
5	272
15	251
9	224
27	149
2	130
4	53
14	29
10	17
3	5
19	4

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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