What Is Surfactant and When Do You Need It In Your Tank? (A Homeowner and Applicator Guide)

Estimated reading time: 13 to 15 minutes

A surfactant is a spray tank additive that helps a herbicide, insecticide, or fungicide stick to a leaf instead of beading up and rolling off by reducing surface tension and improving coverage and absorption. The word surfactant is a mix of the words surface, active, and agent, which describe its purpose.

If you mix and spray weed killers or other pesticides in a home lawn or garden, getting the surfactant right is what keeps product from being wasted and helps you avoid injuring turf and landscape plants. Miss the surfactant when the label calls for one, and you can watch a $60 bottle of Drive XLR8 do half its job. Add the wrong kind, and you can burn cool-season turf on a July afternoon.

This guide covers what a surfactant is, how the different types work, how to read herbicide labels to tell whether one is required, how much to add and when in the mixing order, what damage misuse can cause, and which products make the most sense for homeowners.

Waxy cuticles on grass and weed leaves send unformulated spray solutions rolling off before absorption can happen. That's the whole problem a surfactant solves.

What is a surfactant?

A surfactant (short for surface-active agent) is a chemical compound whose molecules gather at the boundary between two different phases (like water and a leaf surface, or oil and water) and reduce the interfacial tension between them. In practical terms, a surfactant makes water wetter. It flattens spray droplets across a leaf, improves absorption, and lets an active ingredient reach the plant tissue where it works.

That last part matters. According to Iowa State University Extension, spray adjuvants (the umbrella category that includes surfactants) are often required to get consistent postemergence herbicide performance, especially on weeds with thick cuticles.

Chemical structure and the head group

Every surfactant molecule has the same basic architecture as a surface-active molecule: a water-attracting hydrophilic head (the head group) bonded to a water-repelling hydrophobic tail. This amphiphilic nature (two different functional groups on the same molecule) gives surfactants two physical properties: they adsorb at interfaces and can assemble into micelles.

The chemical structure of the head group determines almost everything else: water solubility, electrical charge, wetting properties, foaming behavior, cloud point, and behavior in the water or oil phase.

The head faces the water phase, and the tail faces the oil phase. That simple geometry is why the same molecule can bridge two liquids that normally refuse to mix.

Critical micelle concentration

Push the surfactant concentration high enough and something interesting happens: the molecules stop drifting individually and start forming self-assembled molecular clusters called micelles. The threshold where this begins is the critical micelle concentration, or CMC.

Below the CMC, adding more surfactant keeps lowering the surface tension of the solution. Above it, added surfactant just builds more micelles and the lower surface tension plateaus.

For tank mixing, this means dosing accuracy matters. Underdosing gives you high surface tension and poor coverage. Massively overdosing wastes product and, with some formulations, causes excess foam or leaf burn.

Surface tension: why a spray droplet beads on a leaf

Water molecules pull on each other more strongly than they pull at the boundary between water and a different phase such as air, waxy leaf surfaces, or oils, so a water droplet contracts into a sphere. That's high surface tension. Grass blades, waxy weed cuticles, and most insect exoskeletons repel that sphere the way a raincoat repels rain. Without help, oil droplets and water droplets from your sprayer simply roll off.

Lowering the surface tension of your spray solution is the single biggest job a surfactant does in a pesticide tank. Cut the surface tension in half and a droplet spreads across two or three times more leaf area. More contact, more absorption, more kill.

What a surfactant does to a spray droplet

Add a wetting agent like Alligare 90 Nonionic Surfactant at the labeled rate, and this is how surfactants work inside every spray droplet before it hits the leaf:

1. Surfactant molecules migrate to the droplet surface. Their hydrophobic tails point outward, breaking the water skin.

2. The droplet flattens on impact. Instead of bouncing, it spreads into a thin film that covers stomata, hairs, and the waxy cuticle.

3. The active ingredient moves into the leaf. Nonionic surfactants also help solubilize the herbicide and carry it through the cuticle.

Left: water plus glyphosate alone. Right: the same tank mix with a nonionic surfactant at 0.25% v/v. The right leaf will absorb roughly three times more active ingredient.

Michigan State University Extension has documented this behavior in ornamental crop production, noting that most surfactants added to spray tanks improve wetting, retention, and uptake, but the right choice depends on both the target species and the herbicide chemistry.

How surfactants are classified based on charge

Surfactants are classified based on the electrical charge (or lack of it) on the head group when the molecule dissolves in water. There are four families, and the label on your herbicide is telling you which one to buy. Surfactants are primarily classified as nonionic, anionic, cationic, and zwitterionic types. They are used in large quantities globally, with world production at about 15 million tons per year.

The four charge classes each have different jobs. Getting the class right is more important than getting the brand right.

Nonionic surfactants

Nonionic surfactants (also written non ionic surfactants) carry no electrical charge on the head group. They tolerate hard water, mix cleanly with most pesticide formulations, and are the default recommendation on the majority of postemergence herbicide labels. Products in this category include Dyne-Amic, Alligare 90, and Southern Ag Surfactant for Herbicides. If a label says "add a nonionic surfactant at 0.25% v/v," this is what it wants.

Anionic surfactants

Anionic surfactants carry a negative charge on the head group. Common examples are the sulfates and sulfonates that power most laundry detergents and dish soaps. They foam heavily and clean well, which is exactly why they are the wrong choice for a herbicide tank: excess foam breaks pumps, and the negative charge can precipitate with calcium in hard water.

Cationic surfactants

Cationic surfactants have a positively charged head group. Quaternary ammonium compounds like benzalkonium chloride fall in this class, and they show up in disinfectants, sanitizers, and some fabric softeners. Ionic surfactants of this type are generally not used with herbicides, because they can bind directly to negatively charged herbicide molecules and inactivate them before they ever reach the plant.

Amphoteric surfactants

Amphoteric surfactants (also called zwitterionic surfactants) carry both a positive and a negative charge on the same molecule. The net charge depends on the pH of the solution. They are mild, low-foaming, and skin-friendly, which is why you see them in shampoos, contact-lens solutions, and other personal care formulations. In the chemical industry, they are common examples of specialty wetting agents, but they rarely appear as standalone tank additives for lawn herbicides.

Where surfactants are used outside your spray tank

Surfactants are used in products and processes that need oil and water to work together, where they play a key role. Beyond cleaning products, major uses also include food, cosmetics, pharmaceuticals, and agriculture. Surfactants have the ability to improve the stability and solubility of otherwise poorly water-soluble medications. They pull oil droplets into suspension for oil-in-water emulsions, stabilize the oil-water interface for water-in-oil emulsions in creams and lotions, and act as foaming agents, dispersants, and wetting agents across the chemical industry.

Personal care

The personal care aisle is one massive surfactant showcase. Shampoos, body washes, toothpastes, and shaving creams all use blends of anionic and amphoteric surfactants to lift oils, generate foam, and stay gentle on skin. The zwitterionic surfactants you see on cosmetic ingredient lists are the same chemical family as the amphoterics above.

Antistatic agents

Cationic surfactants also work as antistatic agents in fabric softeners and dryer sheets. The positively charged head group binds to negatively charged fabric fibers, neutralizes static electricity, and leaves the surface feeling softer. Same molecule family as the disinfectant quats, different job.

Nonionic, methylated seed oil, crop oil: which one for which label

Once you know your herbicide requires a surfactant, the next question is which type. Read the label. There are other surfactants used for specialized jobs, but lawn labels usually point you to one of three: nonionic surfactant, MSO, or crop oil.

MSO products like Southern AG MSO, Conic MSO, and Alligare MSO push more active ingredient through waxy cuticles than a plain NIS, but they also increase the risk of turf phytotoxicity when temperatures climb above 85°F.

Cornell Cooperative Extension has documented the trade-off: more penetration, more crop response, sometimes more damage. Water hardness can also affect adjuvant performance, which is one reason labels often favor nonionic options. Match the adjuvant to the label, not to the strongest option on the shelf.

How to read the label to find out whether a surfactant is required

Every EPA-registered herbicide label has an Adjuvants or Spray Additives section, usually right after Mixing Instructions. Look for one of three phrases:

• "A nonionic surfactant is required"- You must add one, no exceptions.

• "For best results, add a nonionic surfactant" - Strongly recommended, and you will see reduced control if you skip it.

• "A surfactant may be added" - Optional, usually because the formulation already contains one.

The Adjuvants section is where the manufacturer tells you exactly which surfactant class, at what rate, and under what conditions. Read it before you fill the tank.

If the label mentions surfactant concentration in percent volume (v/v), do the math for your tank size. For a 4-gallon backpack sprayer at 0.5% v/v, you need about 2.5 fluid ounces of nonionic surfactant. Products like Roundup Pro Concentrate already contain a built-in surfactant loading, so adding more can cause excessive foaming without improving control.

Mixing order and rate: where the surfactant goes in the tank

Tank order matters. Add ingredients in the wrong sequence, and you get precipitates, gels, or clogged screens. Use the WALES order:

1. Wettable powders and water-dispersible granules (WP, WDG)

2. Agitate, then add liquid flowables (SC, F)

3. Liquid solutions and soluble concentrates (SL, SP)

4. Emulsifiable concentrates (EC)

5. Surfactants and adjuvants (last)

WALES: put the surfactant in last, after the tank is half full of water and the pesticide is fully in suspension. Add it earlier, and you make foam before the active ingredient is even mixed.

Fill the tank one-third to one-half with clean water first. Start agitation. Add each product in WALES order, allowing full dispersion between steps. Add the surfactant last, then top off with water and keep agitating right up until you spray.

Rate matters as much as order. Most nonionic surfactants call for 0.25 to 0.5% v/v (roughly 1 to 2 tablespoons per gallon). MSO and crop oil concentrates call for 1.0 to 1.5% v/v (roughly 4 to 6 tablespoons per gallon). Doubling the rate does not double the control. It usually just increases foam and residual surfactant left in the tank.

What happens when you skip it (and when adding one causes damage)

Skip the surfactant on a label that requires one, and you get textbook symptoms: spotty control, weeds that yellow but never die, and a second application two weeks later that costs you as much as the first. Waxy-cuticle weeds like crabgrass, sedges, and mature dandelions are the worst offenders.

On a crabgrass control application with Drive XLR8 or Quali-Pro Sedgemaster, skipping MSO can drop control from 90% to 40% in a single spray.

Adding a surfactant when the label does not call for one, or picking the wrong class, causes its own problems:

• Turf burn on fescue and bluegrass when MSO is used above 85°F

• Phytotoxicity on ornamentals from cationic surfactants that were never meant for foliar use

• Excessive foam and pump cavitation from anionic laundry-style detergents

• Antagonism from mixing cationic surfactants with anionic herbicides in hard water

• Runoff and drift when foaming agents change droplet size and physical properties

The safe rule: match the surfactant class to the label. If the label is silent, a nonionic surfactant at 0.25% v/v is almost never a mistake on lawn and turf work.

Recommended surfactants and the products that need them

For homeowners and residential applicators, stock two adjuvants and you cover 95% of situations. Both are common surfactants for homeowner lawn applications and live in our Nonionic Surfactants & Dyes category alongside the full Weed Killers & Herbicides lineup.

These four adjuvants cover almost every lawn and landscape spray a homeowner will ever mix. Buy the class the label specifies, not the strongest option on the shelf.

Nonionic surfactant (default choice): Dyne-Amic is a blended nonionic and methylated seed oil surfactant that works with the widest range of herbicide labels. It is the pick for glyphosate, 2,4-D mixes, and most broadleaf herbicides. Alligare 90 Nonionic Surfactant is the straight NIS option when the label specifies a 90% nonionic blend and nothing else.

Methylated seed oil: Choose Southern AG MSO or Alligare MSO when the label for Drive XLR8, Sedgemaster, or a sulfonylurea specifies MSO. Cut the rate in the summer if you're spraying cool-season turf.

Spreader-sticker: Bonide Turbo Spreader Sticker adds a resin that keeps the spray film on the leaf longer, useful for pre-rain applications and for pre-emergent herbicides that need to stay in place until the next irrigation cycle.

Hard water and drift control: AirTech Adjuvant combines liquid ammonium sulfate with a surfactant to knock out hard water antagonism (a real issue with glyphosate and 2,4-D in well water).

The Bottom Line on Surfactants

A surfactant is not a nice-to-have. On any herbicide label that requires one, it's the difference between a $60 spray that works and a $60 spray that wastes your afternoon. Read the Adjuvants section on the label, buy the class it specifies (nonionic, MSO, or crop oil), add it last in WALES order, and dose it at the printed rate. Stock a bottle of Dyne-Amic and a quart of Southern AG MSO in the garage, and you're covered for almost every lawn application.

Ready to shop? Browse the full Nonionic Surfactants & Dyes lineup, match one to the herbicide you already own, and put the next spray day on the calendar.# What Is a Surfactant and When Do You Need One In Your Tank? (A Homeowner and Applicator Guide)

A surfactant is a helper you add to your spray tank, so the weed killer, bug spray, or fungicide actually sticks to the leaf instead of rolling off like water on a waxed car. Forget it when the label says to add one, and a $60 bottle of Drive XLR8 can do half its job. Grab the wrong kind, and you can scorch your lawn on a hot July afternoon.

Frequently asked questions

What is the difference between a surfactant and an adjuvant?

A surfactant is one type of adjuvant. An adjuvant is the umbrella term for any spray tank additive that improves pesticide performance: surfactants, crop oils, drift retardants, water conditioners, defoamers, and pH buffers. Every surfactant is an adjuvant, but not every adjuvant is a surfactant.

Can I use dish soap as a surfactant in my sprayer?

No, not for herbicides. Dish soap and purpose-built surfactants are chemicals formulated for very different jobs. Dish soap is an anionic surfactant loaded with fragrances, dyes, and salts - added substances that can antagonize the herbicide, precipitate in hard water, and foam heavily.

Anionic surfactants are great for effectively removing dirt and grease, but don't work well with a spray tank. Use a purpose-built nonionic surfactant at the label rate. A quart of Alligare 90 costs less than $25 and lasts through many spray seasons.

What rate of nonionic surfactant should I use?

Follow the herbicide label first. If the label specifies 0.25% v/v, use 0.32 fluid ounces per gallon. If it specifies 0.5% v/v, use 0.64 fluid ounces per gallon. When the label just says "add a nonionic surfactant," 0.25% v/v is a safe default for lawn and turf herbicides in most conditions.

Do I need a surfactant with Roundup?

Consumer Roundup formulations already contain surfactant. Professional concentrates like Roundup Pro Concentrate include a built-in surfactant loading and do not require additional NIS in most applications. Generic glyphosate concentrates often do require an added nonionic surfactant. Always check the label of the specific product in your tank.

Will a surfactant damage my lawn?

A nonionic surfactant used at the label rate is safe on established cool-season and warm-season turf. Biodegradability and environmental impact are also important design considerations, especially in water systems. In some cases, surfactants may be deposited into land and water systems. Some fluorosurfactants such as PFOA are non-biodegradable and persistent, and some breakdown products such as nonylphenol are endocrine disruptors.

Damage risk comes from using MSO or crop oil concentrate above 85°F, from using cationic (fabric-softener style) surfactants that were never meant for foliar use, or from doubling the label rate on stressed turf.