As you look over your chemical prepay, did you include an adjuvant? Facts are, adjuvants are worth the money, and here’s why.
Adjuvants have a number of jobs. They help condition water, stop evaporation, even out spread patterns, and above all, adjuvants make sure those expensive herbicides get into the weeds to stop growth.
Adjuvants are the difference between the herbicide being lost to rolling off the leaf surface and getting down into the leaf. In order for a herbicide to be effective, it has to get through the outer layers of the leaf and into the plant cells. This means it has to get through the outer waxy layer (cuticle) and the cell wall, where it can reach its specific site of action. This is the primary reason why adjuvants pay for themselves. It's harder to get a herbicide into a plant than you might think!
Barriers to Entering the Leaf
The leaf's outer layer, called the cuticle, is made of wax. It prevents the plant from drying out and protects the leaves from excessive UV rays, so it’s naturally tough to penetrate, making it difficult for herbicides to get through. There are 2 main paths through this cuticle.
Every plant species differs in cuticular structure, and environmental conditions can influence how this layer changes daily. For example if it gets hot, the waxy cuticle layer can become thicker, protecting the leaf moisture, and that also makes it harder for herbicides to enter.
2 Main Paths:
Lipophilic Pathway (fat-soluble) primarily the way herbicides enter leaf surfaces.
Polar Pathway (water-soluble) primarily the way water and nutrients enter leaf surfaces.
Think of a plant leaf as having layers: some parts mix well with water, and others with oil. For a herbicide to work, it has to move through all those layers to reach the inside of the plant cell. Some herbicides, like glyphosate, mix better with water than with oil. That can make it harder for them to move through the waxy (oily) outer layer of the leaf.
This is where an adjuvant helps.
An adjuvant acts like a “bridge.” It helps the herbicide work with both water‑loving and oil‑loving parts of the leaf. Because of that, the herbicide can move through the waxy cuticle, penetrate the cell wall, and reach the inside of the plant, where it can do its job.
In simple terms:
An adjuvant helps the herbicide penetrate the plant more easily, allowing it to kill the weed.
Adjuvant Jobs
Water Conditioners are adjuvants that do just that: they condition hard water so that herbicides don’t get tied up by cations. Water conditioners prevent the herbicides from being tied up, so they don’t just sit on the leaf surface; allowing the herbicide to actually do the job they were meant to do.
An adjuvant containing “sticker/spreader” components (wetting agents) function just as the name suggests. Sticker/spreaders, spread the herbicide across the leaf surface. Similar to how rain droplets bead off and keep them on the leaf until they are absorbed. Labels often mention “humectancy,” which indicates the enhanced ability to retain water and slow droplet evaporation before entering the leaf. This aids in overcoming the waxy and hairy surfaces of many weed species, preventing herbicide droplets from 'shedding' immediately, as they would without an adjuvant. In other words, the droplets stay wet a little longer and allow the herbicide to get into the leaf surface.
Crop oil Concentrates are another adjuvant used in spray applications. They help soften the waxy layer, allowing easier entry through it for the herbicide. This is why crop oils “heat up” a mix and can cause crop damage; the implications of not controlling the weeds or ending up with resistant weeds are oftentimes, much worse than the visual crop damage that the crop should be able to quickly outgrow. Crop oils also provide better leaf coverage and keep the leaf wetter, longer than water alone. Crop oils can be more detailed. Follow along to hear more.
Different growing conditions require different crop oils for the best herbicide performance. Drought conditions create tougher weed control challenges. Plants, both weeds and crops, under drought stress produce a thicker cuticle, which is a natural defense response. They are trying to save water and overcome drought stress. Using an MSO (methylated seed oil) has the advantage over a traditional COC (crop oil concentrate) by helping the herbicide enter the plant faster, even as the plant works to make entry through the cuticle more difficult.
When spray conditions are good, we might only need a NIS (non-ionic surfactant). An NIS primarily helps improve herbicide leaf coverage, by reducing the surface tension of the water allowing it to spread out further on the leaf allowing more area for penetration into the leaf. They also typically have ingredients that perform the “sticker/spreader” role and keep the droplet on the leaf from being too quickly evaporated or rewetted by dew or other moisture. If you’re not sure which COC is best for your operation, ask a Liqui-Grow Agronomy Field Advisor!
What adjuvant to use under what growing conditions
Environmental Conditions that reduce herbicide uptake:
- Low Humidity/High Evaporation (NIS/Humectant)
- High Humidity/Heavy Dews (Spreader/Sticker)
- Hot, Dry Weather (COC, MSO)
- Cool, Wet Weather (NIS)
- Windy Conditions (Drift Reduction/Deposition Aid)
- Hard Water used as a carrier (NIS/AMS water conditioner)
Plant Physiology that reduces herbicide uptake:
- Structure of Cuticle
- Thickness of the Cuticle
- Hair on leaf surface (can suspend droplets so they evaporate before touching the leaf)
- pH of the leaf surface
Drift/Deposition Adjuvants
Some adjuvants can reduce drift and also penetrate the canopy. These products can be added to maintain droplet size and help reduce evaporation. These same products may be able to penetrate the canopy and increase leaf coverage, ensuring better herbicide weed control. These products are also very important when utilizing in-season applications or fungicide applications.
Tank Mixes and Labels
When you’re deciding which adjuvant to use, the tank‑mix guide and the herbicide label are the best places to start. Herbicide labels will tell you which adjuvants work best with that product, and sometimes they even give different recommendations depending on the weather or field conditions.
If you’re mixing several products in the same tank, remember: the adjuvant you choose can affect how the other products behave. That’s why you always need to think about how everything in the tank will interact.
It’s also important to follow the right mixing order. A water conditioner should always be added to the water first. Oils like MSO or COC, or drift‑control products, usually go in last. Doing a quick jar test is a great way to see herbicide compatibility and correct mixing order. Always check the label first.
And above all, follow the label. If you’re unsure about anything, reach out to a Liqui‑Grow Agronomy Field Advisor. They can help you make the right call.
Summary
By now, you’ve probably noticed that adjuvants are almost as important as the herbicide itself. They help the herbicide do its intended job, which means you get better weed control and help slow down the chances of weeds becoming resistant in the future.
Here’s something important: using an adjuvant doesn’t mean you can lower the herbicide rate. The adjuvant helps the herbicide enter the plant by overcoming barriers that would normally block it, such as the waxy leaf surface or tough weather conditions. Once the herbicide gets inside the plant, the rate you applied matters a lot. That’s what determines whether the herbicide can reach and shut down the plant’s specific target site.
So don’t cut herbicide rates, thinking the adjuvant will make up for it. Its job is to help the herbicide get where it needs to go, not replace the amount of herbicide you need.
Learn More!
Watch our LEAD Academy video all about controlling Waterhemp and other resistant weeds.
Questions? Give us a shout!
Text us at 564-220-2508 or email questions@liqui-grow.com.