Adjuvants for Post-Emergence Herbicide Applications in Soybean

Sithin Mathew, Weed Science Graduate Student, Eric Yu, UMN Extension Crops Educator, and Debalin Sarangi, Extension Weed Scientist

Herbicides often require the use of adjuvants to maximize weed control efficacy and minimize application-related risks. Although some herbicide formulations contain built-in adjuvant packages, few are designed to optimize performance across the wide range of environmental and application conditions. Therefore, the applicator often needs additional adjuvants to optimize the herbicide application for the specific conditions of the area being treated. 

The most commonly used adjuvants can be grouped into four categories: 1) activator adjuvants [e.g., nonionic surfactant (NIS), crop oil concentrate (COC), and methylated seed oil (MSO), etc.], 2) water conditioners [e.g., ammonium sulfate (AMS), and volatility reduction agent (VRA), etc.], 3) spray solution modifiers [e.g., antifoam agents, and drift reduction agents (DRA)], and 4) adjuvant mixtures. Adjuvants can enhance herbicide activity by improving spray retention, spreading, penetration, absorption, and overall weed control. For more information on adjuvant use and function in herbicide applications, see the following Crop Protection Network article. Additional information on the history of adjuvants and best management practices can be found in this Crop News article.

Correctly using adjuvants is important because using an incorrect type or rate can result in poor weed control and/or crop injury. The appropriate use of an adjuvant, including adjuvant selection and the amount required, may vary by herbicide and environment. The herbicide label should be the first place to look to determine if an adjuvant is required, the correct type needed, and the recommended rate. If multiple herbicides are being applied, consult the label of each product, paying particular attention to guidance on adjuvants, tank mix partners, and any restrictions or “do not” statements. When label directions differ among products, follow the most restrictive label requirements to ensure compliance and minimize the risk. In this article, we summarize adjuvants commonly recommended for widely used post-emergence herbicides in soybean (Table 1). ALWAYS CONSULT HERBICIDE LABELS BEFORE APPLICATION TO ENSURE COMPLIANCE!

Table 1. Adjuvants (NIS/COC/MSO with UAN/AMS) for commonly used post-emergence herbicides in soybean

Herbicide	NISa or	COCa or	MSO	With UANa, b or	With AMSa, b
Anthem Maxx	0.25%	1-2 pts/A and concentration must not exceed 2.5%	1-2 pts/A and concentration must not exceed 2.5%	1-2 qts/A	8.5-17 lb/100 gal
Arrow 2EC	-	1% but not less than 1 qts/A	-	1-2 qts/A	2.5-4 lb/A
Assure II, Targa	0.25%	1-2%	-	2-4 qts/A	2-4 lb/A
Basagran 5L	0.25-0.50%	1%	1%	1.25-2.5%	8.5-17 lb/100 gal
Cadet	0.25%	1-2 pts/A and concentration must not exceed 2.5%	1-2 pts/A	1-2 qts/A	8.5-17 lb/100 gal
Classic	0.25%	1%	1%	2-4 qts/A	2-4 lb/A
Cobra	0.25%	1-2 pts/A	1-2 pts/A	1 qts/A	2.5 lb/A
Enlist Duo/ Enlist One (for Enlist soybean)	0.25%	1-2 pts/A	1-2 pts/A	-	8.5-17 lb/100 gal
FirstRate	0.125-0.25%	1.2%	1.2%	2.5%	8.5-17 lb/100 gal
FlexStar	0.25-0.5%	0.5-1%	0.5-1%	1-2.5%	Minimum 8.5 lb/100 gal
Fusilade DX	0.25-0.5%	0.5-1%	0.5-1%	1 gal/A	-
Harmony SG	1-2 pt/100 gal	1-2%	0.5%	2-4 qts/A	2-4 lb/A
Liberty Ultra (only for Liberty Link soybean)	-	-	-	-	1.5-3 lb/A
Perpetuo	-	1 pts/A	1 pts/A	1-2 qts/A	2-2.5 lb/A
Poast	-	2 pts/A	1.5 pts/A	4-8 pts/A	2.5 lb/A
Pursuit	0.25%	1.25%	1%	1.25-2.5%	12-15 lb/100 gal
Raptor	0.25%	1-2%	1-2%	2.5%	12-15 lb/100 gal
Resource	-	1 qts/A	1 qts/A	1-2 qts/A	2-2.5 lb/A
Roundup PowerMax3 (for Roundup Ready soybean)	0.25-0.5%	-	-	-	8.5-17 lb/100 gal
Scepter 70DG	0.25-0.5%	1-2%	0.5-1%	1.25-2.5%	8.5-17 lb/100 gal
Select MAX	0.25%	1% or 1 qt/A	1% or 1 qt/A	-	8.5-17 lb/100 gal
Sequence (for Roundup Ready soybean)	-	-	-	-	8.5-17 lb/100 gal
Stryax/Engenia/Taviumc (for XtendFlex soybean)	0.25%	-	-	-	DO NOT MIX
Ultra Blazer	1-2 pts/100 gal	1-2 pts/A	1-2 pts/A	4-8 pts/A	2.5 lb/A
Varisto	0.25%	1-2%	1%	2.5%	12-15 lb/100 gal
Warrant Ultra	0.25-0.5%	0.5-1%	1%	DO NOT MIX	DO NOT MIX
Zalo (for Liberty Link soybean)	0.25-0.5%	1%	1%	DO NOT MIX	3 lb/A

^aAbbreviations: NIS is nonionic surfactant (% v/v or dose specified), COC is crop oil concentrate (% v/v or dose specified), MSO is methylated seed oil (% v/v or dose specified), UAN is urea ammonium nitrate, and AMS is spray grade ammonium sulfate.

^b Whenever the label states “at recommended rates” or “specified use rates” for AMS they are referring to this rate of 8.5 - 17 pounds per 100 gallons. DO NOT MIX if not specified in the label.

^cApplications of this product (Stryax/Engenia/Tavium) must include an oil emulsion Drift Reduction Agent (DRA) at a concentration of 0.3%, and a qualified pH buffering Volatility Reduction Agent (VRA)