The Science Behind Activator Adjuvants: Better Spray Coverage, Better Results

It’s important to understand what is in your spray solution and its role to achieve optimum results.

What are Spray adjuvants? 

Spray adjuvants are any material added to a pesticide spray solution that modifies the biological activity or physical characteristics of the spray solution.  

Although there are many different categories of adjuvants, this list will briefly discuss the purposes of activator adjuvants and spray solution modifiers in enhancing performance of POST spray applications.

What are Activator Adjuvants? 

Activators Adjuvants increase pesticide activity through increased spray retention, droplet spreading, and/or absorption. The following are types of activator adjuvants. 

Surfactants

Surfactants is a shortened form of the phrase surface acting agent. They are a class of activators that are primarily known for their ability to reduce surface tension of a spray solution. Water by itself has a high surface tension because water molecules are highly polar and are attracted to each other. They form bonds and this cohesion causes droplets to form into a tight spherical shape. When surfactants are added to water, they mix among the water molecules and replace the cohesive bonds among the water molecules. Surface tension is reduced, and the droplet is able to better spread on the target surface.

Crop Oil Concentrate (COC)

Crop Oil Concentrate (COC) are vegetable or petroleum oils whose primary function is to enhance the uptake of an herbicide into the plant. COCs contain special surfactants called emulsifiers that help the oil mix with water. COC formulations contain a minimum of 80% oil mixed with 15 to 20% surfactant.

COC adjuvants reduce the surface tension of the spray droplet on the leaf surface and increase retention and the penetration of herbicides through waxy leaf cuticles. Crop oils are typically used with contact herbicides, like Protoporphyrinogen oxidase PPO inhibitors. Together they increase herbicide penetration within the plant and reduce surface tension for a more effective herbicide application.

Methylated Seed Oil (MSO)

Methylated Seed Oil (MSO) are adjuvants that consist of a methylated vegetable or seed oil (i.e., canola, cotton, linseed, soybean) mixed with an emulsifier to allow for dispersion in water. MSO adjuvants reduce the surface tension of the spray droplet, increase retention, and increase the speed of herbicide absorption.

MSOs can be more aggressive in dissolving the leaf cuticle than COCs and result in greater and faster herbicide absorption into the plant. This can also result in greater crop injury compared to other adjuvant types.

High Surfactant Oil Concentrate (HSOC)

High Surfactant Oil Concentrate (HSOC) contains at least 50% of either petroleum oil or a methylated seed oil combined with 25 to 50% surfactant. HSOC products have properties of a surfactant and an MSO or COC. Where the pesticide label does not provide specific guidelines for use, HSOC adjuvants should be used at half the rate (typically 0.5%v/v) of COC or MSO that is on the pesticide label. This reduces the possibility of crop injury.

The Takeaway

Adjuvants are essential tools that enhance the activity of pesticides beyond what can be included in the pesticide formulation alone. Activator adjuvants help to: 

• Improve the spray efficacy in different environmental conditions and are recommended on product labels  

• Lower surface tension, which can reduce droplet bounce and enhance droplet spread 

• Increase pesticide absorption through cuticles 

• Enhance the herbicide’s ability to withstand adverse environmental conditions such as rain or bright sunshine

To determine the appropriate adjuvants to include in a specific application, consult the product label, visit with your Agronomy Sales Enablement team member, or contact your Simplot Grower Solutions Crop Advisor.

Authors

Click to read more about the authors