What is Methylated Seed Oil and How Does it Work?

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What is Methylated Seed Oil and How Does it Work?

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The control of weedy and invasive plants is a battle that is fought by many managers of terrestrial and aquatic habitats. This battle must be waged to prevent the proliferation and establishment of weedy and invasive plants that lower the potential of a variety of habitats. In addition, uncontrolled weedy and invasive plants can impact humans in other undesirable ways.

Every yearin the spring, the challenge to control weeds begins and is most intense in crop production. Crop production managers control weedy and invasive plants using three approaches: preplant control, preemergence control and postemergence control.

  • Preplant control–application of an herbicide or other control measure before the crop is planted.
  • Preemergence control– application of an herbicide or other control measure after the crop has been planted but before it emerges.
  • Postemergence control–application of an herbicide or other control measure after the crop and weed have emerged.

These weed control practices usually provideoptimal weed management that leads to abundant harvests and yields. These practices are successful becausethe control measures are applied early in the season when most of the weeds are young and vulnerable.

The challenge arises when there are weedy and invasive plants that avoid early season control, are not detected soon, and are harder to control as the crop growing season progresses. Often called escapes, this group of plants are a challenge to control and if let to mature they will go to seed and replenish the soil seedbank.

Escaped weeds must not be allowed to thrive but controlling them in the heat of summer is difficult.

Enter methylated seed oil (MSO).

What is methylated seed oil?

AMSO is vegetable oil that has been modified through a process of esterification. Therefore, MSO is an oilbasedsurfactant. Oil based surfactants:

  • Slow the drying of the herbicide droplet on the leaf surface, which increases the potential for herbicide absorption.
  • Can improve penetration into the leaf by modifying (solubilizing) leaf surface waxes.
  • Can cause injury (leaf burn) if applied with a herbicide under less than ideal moisture conditions.

What is the difference between methylated seed oil and other oil basedsurfactants?

There are three categories of oil basedsurfactants: crop oil concentrates, vegetable oil, and crop oil.

Crop oil concentrates (COCs) are primarily composed of emulsifiable petroleum-based oil and a small percentage of a nonionic surfactant. COCs are often known as penetrating agents.

Vegetable oils are primarily a crop oil such as cotton, linseed or soybean oil and a small percentage of a non-ionic surfactant. MSO is classified as a vegetable oil.

Crop Oils are not vegetable based. They are more than 95 percent paraffin or naptha-based petroleum oil with 1 to 2 percent nonionic surfactant. Basic crop oils are not commonly used with herbicides.

How is methylated seed oil made?

MSO is manufactured in a process that attaches methanol units to a vegetable-based oil. The attachment of the methanol to the vegetable oil alters the hydrophilic/lipophilic balance (HLB) of the seed oil.

  • The HLB describes the ability of a surfactant to associate with hydrophilic and lipophilic compounds.
  • HLB values range from 0 – 20, and most surfactants used with postemergence herbicides have HLB values of 12 or greater.
  • Surfactants with a high HLB associate better with water soluble compounds than oil soluble compounds.

What is methylated seed oil used for?

MSOis used to maximize the performance of most postemergence herbicides.

Known for its ability to rapidly spread and penetrate leaf surfaces, MSOscan decrease surface tension of herbicide spray droplets and increase the wetting capability on very waxy and hairy leaves leading to increased herbicide absorption.

Some reports have shown that MSO enhances the efficacy of several herbicides on certain weed species by increasing the absorption of the herbicides by weeds. For example, using MSO helped improve herbicidal phytotoxicity on difficult-to-control common lambsquarters and giant foxtail plants in soybean.

Advantages of using MSO surfactants

MSO surfactants:

  • Maximize the performance of most post-emergent herbicides.
  • Are a replacement for non-ionic surfactants and crop oil (petroleum oils).
  • Rapidly penetrate plant leaf tissue.
  • Are less viscous than typical plant oils.
  • Resist evaporation and help retain spray mixture on plant surfaces to enable maximum penetration of herbicide active ingredient.

Example of MSO-based surfactants

  • SunEnergy®
    • Nonionic spray adjuvant consisting of a blend of MSO, organosilicones, and emulsifiers.
    • Enhances the performance of postemergence herbicides through wetting and penetration at lower rates than regular surfactants.
  • Cide-Kick II M®
    • Nonionic spray adjuvant consisting of a blend of MSO, limonene, and emulsifiers.
    • Wetting, activating, and penetrating agent that allows more effective uptake of herbicide.
    • Helps breakdown the waxy cuticle on leaf surfaces.
    • Helps penetrate the bud and bark area of woody brush.
  • Sun Wet®
    • Nonionic spray adjuvant that is a blend of MSO and emulsifiers.
    • Designed to enhance the performance of postemergence herbicides through wetting and penetration.

Further Reading


Nelson, K.A., K.A. Renner, and D. Penner. 1998. Weed control in soybean (Glycine max) with imazamox and imazethapyr. Weed Science 46(5): 587-594. DOI: https://doi.org/10.1017/S0043174500091141

Brewer International has been a leader in land and water chemistry since the 1980’s and for over 40 years has proudly served it’s national and regional distributors. 

Our products are used widely across the United States in agriculture, aquatics, forestry, rights of way, and land management. 

Our customers trust our dedication to quality ingredients, tried and true formulas, and positive outcomes.

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