Spray adjuvants. 28

Spray Tank Adjuvants.

A spray or herbicide adjuvant is an additive that improves the effectiveness of a turf chemical or fertiliser. Spray adjuvants include defoamers, spreaders, stickers, and water conditioners. These:

• Wet surfaces faster.
• Give a more even product distribution over the leaf.
• Increase the retention of a spray on a leaf, and improve foliar uptake.

What are Spray Tank Adjuvants?

• Spray and herbicide adjuvants are compounds that you add to a spray tank. These improve how well a chemical mixes, how it behaves on a leaf or how well it works.
• Some glyphosate formulations such as (Rapid Fire) already include an adjuvant. In other cases, these are stand-alone herbicide adjuvants that you add to a spray tank.
• The use of adjuvants is common in Sydney and Canberra due to the unique climates that turf managers face.

Adjuvant examples:

• Some herbicide adjuvants counter issues with hot dry weather, that can affect herbicide performance.
• Others lower a spray tank pH so that products work better.
• A non-ionic surfactant is recommended with Proforce Duke herbicide, or Recondo herbicides. These are both sulfonylurea herbicides. The use of a herbicide adjuvant with these improves leaf coverage, and so gives better results.

At the end of this article is a list of adjuvants to use with turf products.

Check these links out for more on soil adjuvants and Soil wetting agents. For more detail on what adjuvants you can use with which turf chemical see this Turf Chemical Guide.

Do Spray Adjuvants work?

The simple answer is yes, but only if you use the right one. For an example of how effective herbicides adjuvants can be, I’m going to use Quinclorac the active in Quinstar. 

• Quinclorac with no adjuvant does not control Sowthistle¹Zawierucha, JE. 1998. The Basis for the Differential Response of Several Weed Species to Quinclorac. Michigan State University. Department of Crop and Soil Sciences.
• All adjuvants give better control with Quinclorac except for a modified polysiloxane.
• Quinclorac works nearly twice as well on Green Foxtail when you increase the spray pH from 2.6 to 7.3²Woznica Z, Nalewaja JD, Messersmith CG, Milkowski P. Quinclorac Efficacy as Affected by Adjuvants and Spray Carrier Water. Weed Technology. 2003;17(3):582-588. doi:10.1614/0890-037X(2003)017[0582:QEAABA]2.0.CO;2.

The Benefits of Spray Adjuvants:

• They help products mix better in a spray tank.
• They improve the contact between a chemical and the target.
• Water conditioners improve how well a chemical works.
• Herbicide adjuvants increase the rate a chemical moves through the leaves and the stomata.
• Adjuvants increase chemical safety. They increase chemical selectivity.
• They can reduce the chemical rate by 5 to 10 times and reduce costs.
• An adjuvant costs a lot less than a chemical does. A USA study shows that the use of adjuvants can reduce costs by up to 40%.

In many cases use of these improves how well a turf chemical works. The graph below shows how these can improve the performance of Azoxystrobin.

Thanks to the USDA Agricultural Research Service for these videos.These show how the right adjuvant can improve chemical movement into a leaf.

The Negatives of Spray Adjuvants.

These can also be some negatives when you use these.

• They can reduce how well a chemical works. For example a water conditioner or pH buffer, doesn’t always improve the results you get.
• They can extend the life of a chemical so it takes longer to breakdown. This means they persist longer in the environment.
• Some are even dangerous themselves. This was the case with the carrier in older Glyphosate formulations.

In fact there is no perfect spray adjuvant. Nothing will always make a chemical perform better in all situations.

History of Spray Adjuvants.

Below is the 2013 APVMA data for chemical use. This is by dollar value, vs the 2020-21 figures. Both the number of products, and the value of adjuvant sales show a huge increase.

When these products were first introduced they had little data to support their claims. These were simple soaps, as well as vegetable, and petroleum-based oils.

However, over time there has been a significant amount of investment. This has lead to major advances in understanding how these products work.

How to Use Spray Adjuvants.

These have several modes of action. For example, they can increase the retention, spread, and movement of chemicals into plants. Some, also have the ability to affect spray droplet size, reduce foam or even alter the water pH.

Activator Spray Adjuvants.

These improve chemical performance. They can for example, increase the uptake of a chemical. Surfactants, crop oils, crop oil concentrates (COCs), vegetable oils, methylated seed oils (MSOs), petroleum oils, N fertilisers, and silicone derivatives, are all in this class.

Spray Modifiers.

Spray modifiers include spray stickers, spreaders, and drift control agents. These change the physical nature of a spray solution.

Utility Adjuvants.

Ultility adjuvants include products like defoamers, spray buffers, and water conditioners. These increase the conditions where you can use a turf chemical.

Surfactants.

• These are the most common group of spray adjuvants.
• The term Surfactants comes from SURFace ACTive ageNTS.
• They reduce the surface tension of a spray solution, and how a spray behaves.
• You often find these in use as herbicide adjuvants for weed sprays.
• If you reduce the surface tension of water, the solution spreads out over the leaf, and does not bead on the surface.

The surface tension of water is 72 dynes/cm. Surfactants reduce the surface tension down to 20 to 30 dynes/cm. This reduction in surface tension means better uptake as the spray is in contact with the leaf surface for longer.

This is the reason why you use non-ionic surfactants for Duke herbicide, Recondo or Tribute Selective.

Examples of non-ionic surfactants include: EO-PO Block copolymers, organo-silicones, and alkylpolyglucosides (APG).

Surfactants also change the viscosity, and structure of leaf and stem waxes. This makes it easier for a herbicide to enter the plant.

How Do Spray Surfactants work.

• They allow a more uniform spread of the spray solution over the leaf surface.
• Spray surfactants act as spray stickers.
• They increase the movement of chemicals past leaf hairs etc.
• They prevent spray deposit crystallisation.
• Increase the time for a solution to dry, and water retention.

Several factors affect the results of a spray application. Key amongst these are:

• The nature of the target plant.
• Any interactions between the adjuvant and a chemical.

The balance between the hydrophilic (water-soluble) and lipophilic (oil soluble) components of an adjuvant is called the Hydrophillic –Lipophilic Balance (HLB).

The HLB is a key factor to consider when you choose a product. It is a way to describe how much a surfactant loves water (hydrophilic) or oil (lipophilic).

• If you match the HLB of an adjuvant to the chemical nature of a pesticide and the target, it ensures you get better results.
• It is best to use a lipophilic adjuvant with a lipophilic chemical and vice versa.
• Oil soluble herbicides work best with herbicide adjuvants that have an HLB of 1 to 10.
• Water soluble herbicides work best with surfactants with an HLB of 10 to 20.

Table of HLB Ranges for Spray Adjuvants.

There are three main types of spray adjuvants for turf:

• Nonionic (no charge).
• Anionic (negative charge).
• Cationic surfactants (positive charge).

Both anionic and cationic surfactants are not often used on turf, because they can cause damage to turfgrass.

Non-ionic Surfactants.

• Non-ionic surfactants are the most common of these. As well as being hydrophilic (they love water), they do not have an ionic charge. This means they tend to have no negative effect on a spray mix. All wetters, spreaders, and organosiloxanes are in this class.
• Non-ionic surfactants reduce the surface tension of a spray solution. They have a direct effect on the leaf cuticle, and change the nature of a leaf surface.
• When you use Organosiloxanes (Proforce Scrubwet), they reduce the surface tension, and form a thin layer on the leaf surface.
• Their unique properties, mean that these are often included as wetting agents for weed sprays. Spray solutions are able to move through the stomata, and they effect the amount of chemical that passes through the cuticle.
• This super spreading property means that they are nearly impossible to wash off a leaf surface. Even if it rains.
• Organosilixone adjuvants improve the uptake of phosphorous acid into Pinus radiata needles³Rolando C, Gaskin R, Horgan D. et al. The use of adjuvants to improve uptake of phosphorous acid applied to Pinus radiata needles for control of foliar Phytophthora diseases. N.Z. j. of For. Sci. 44, 8 (2014). https://doi.org/10.1186/s40490-014-0008-5.
• Ongoing work is even looking at these to help with the control of adult stem weevil.

Oils.

The three types of oil-based adjuvants are:

• Crop oils.
• Crop oil concentrates.
• Methylated seed oils.

These are popular as a herbicide surfactants because they increase the movement of a spray into a plant, and reduce surface tension.

Crop Oils.

• These are also known as petroleum oils, but do not contain any vegetable oil.
• They contain a maximum of 5% surfactant.
• Crop oils, improve the movement of a chemical either through a plant’s waxy cuticle or an insect’s tough, chitinous shell.
• You often see traditional crop oils in use for insect and disease control, and rarely with herbicides.

Crop Oil Concentrates (COCs).

• These contain 10 to 20% non-ionic surfactant.
• COC’s act as penetrants and are excellent spreading agents.
• They are good herbicide adjuvants. They help make some of the less-soluble herbicides more soluble in water.
• They are often used to target grass weeds like Summer Grass.
• Examples are Hasten and Banjo spray adjuvant. Both of these are a combination of vegetable oil and non-ionic surfactant.

Methylated Seed Oils (MSOs).

• These are oil-based surfactants, and can cause leaf burn and phytotoxicity.
• Examples include Voltage MSO.
• These are the most active of the herbicide adjuvants. They work best on large weeds or those under drought-stress that are not growing.

This type of herbicide surfactant has the following benefits:

• When you use this theset they increase the drying time on a leaf surface. This increases the time for herbicide uptake.
• These herbicide adjuvants solubilize leaf waxes. This improves chemical penetration of a leaf.
• They improve the control of large weeds.
• You get better control of weeds under stress or that are not growing.
• These work well on difficult to control weeds.

MSO’s improve the performance of Quinclorac when you use it for Spurge or Summer grass. This is because an MSO + Quinclorac does two things:

• It enhances chemical movement into the leaf.
• They keep a chemical in solution. This prevents it from crystalising on the leaf surface.
• You need 25% less Nominee for Winter Grass control when you use it with an MSO spray adjuvant⁴Lycan, DW. & Hart, SE. (2005). Cool-season Turfgrass Response to Bispyribac-Sodium. HortScience, 40(5), 1552-1555. https://www.doi.org/10.21273/HORTSCI.40.5.1552.

Water Conditioners or Spray Buffers.

• The ideal water pH for most chemicals is in the range of 4.0 to 6.5, and it is best between 5.5 to 6.5.
• Most chemicals work better in the 4 to 6.5 pH range due to alkaline hydrolysis.
• Above a pH of 7, some chemicals tend to be prone to this.
• An example of this are iprodione-based fungicides like Voltar® 500SC. This has a half-life of 48 minutes at pH 7.
• An outlier to this are the Group 2 herbicides, which favour a pH of 7 or greater.
• When you use a water conditioner or spray buffer like Manta Ray it lowers the water pH. This means it is ideal to use as a surfactant for herbicides like Glyphosate.
• The end result is fewer re-sprays, better performance, lower chemical use and lower labour costs. 

Water pH.

• Water quality changes through the year so you need to check it regularly.
• Generally speaking tap water in Australia is at a pH of above pH 7.
• If you use water at this pH in your spray tank you may need to use a spray buffer.
• Do not get into the habit of using a spray buffer in every tank mix. For example, at a low pH, 2,4-D amine tends to drop out of solution or form a gel.
• If you don’t have a current water analysis there are some options. There are some great online tools available. Simply fill in your post code and it will give you the results.

Sydney Water quality

Melbourne Water quality

South East Melbourne Water quality

South East Queensland Water quality

Canberra Water quality

Table of Water pH Spray Tank Stability.

Anti-foam or Defoamers.

Defoamers reduce the build up of foam. This can be a serious issue in soft water areas like the ACT. Polydimethylsiloxane is the active in Foam-aid. It prevents foam, and removes any foam that forms while you mix.

Deposition and Drift Control Agents.

Deposition aids are also called spray stickers. These increase how long a chemical lasts, once you apply it to a leaf surface. Other properties include:

• They can reduce evaporation.
• Increase UV stability. Bond adjuvant or Octane are examples of these.
• Drift control agents reduce spray drift, by increasing the spray droplet size.
• Droplets with a diameter of 150 microns or smaller tend to drift. The use of drift control agents means you can better target your spray.
• They bind with water molecules to form larger spray droplets.
• The best of these appear to be products based on guar gum.

Since 2010 there has been a law to assess new chemicals for the potential risk of spray drift. As a result of this, no spray buffer zones are now on labels of products like Specticle herbicide and Numchuk Quad.

Modifying Spray Drop Size.

• Wetting agents tend to reduce the spray drop size.
• Oil-based adjuvants tend to increase it.
• When you spray, consider your nozzle selection, the spray pressure, boom height, and also the weather conditions.
• Don’t rely solely on these to deal with off-target drift.
• Water-based sprays are the standard means to apply chemical sprays.
• The aim is to use a specific-sized spray for the best results.
• Drift occurs if droplets are too small.
• If spray drops are too large they will run off the target.

Foam Markers and Colourants.

You use foam markers to see where you spray without having to use a marker dye. This helps avoid overlap when you apply chemicals.

You use colourants such as Blue spray indicator as marker or indicator dyes to identify areas that you have already sprayed. This is in contrast to turf pigments that you can use as broad acre masking agents, and also to stimulate growth.

Spray Tank Cleaners.

Spray tank cleaners remove nasty residues that remain after you spray. Tank cleaners often contain sodium tripolyphosphate. You should always use these to clean a spray tank if you use a non selective herbicides like glyphosate or the sulfonylureas.

Ammonium Fertilisers.

• Urea-ammonium nitrate (UAN), and ammonium sulphate (AMS) reduce the negative effects of hard water.
• Fe, Zn, Mg, Na, K, and Ca can react with herbicides like 2,4-D and glyphosate, to form insoluble precipitates.
• In hard water areas, you should consider the use of crystalline ammonium sulphate as a herbicide adjuvant. This will stop the formation of the insoluble Ca form of Glyphosate.
• Don’t use granular or standard ammonium sulphate with Glyphosate. This is because they both contain impurities that will give poor results.
• When you add crystalline ammonium sulphate as a herbicide adjuvant to a tank the temperature of the solution drops. This what is called an endothermic reaction.
• Because of this, be aware that in the Winter, this drop in temperature can make tank mixing difficult. For this reason, fill the tank at least three-quarters full before you use ammonium sulphate as a herbicide surfactant.

Our chemical and irrigation suitability water analysis calculates exactly how much ammonium sulphate you need.

Table of The Ammonium Sulphate Rate for Hard Water.

• Turf is very efficient at taking up NH4 ions.
• This is because when turf takes up NH4 it is at the expense of H+ ions.
• When this happens the H+ ions tend to move to the outside of plant cells.
• When this occurs, there is a drop in the pH.
• The use of NH4 increases herbicide uptake, and creates a pH gradient across the cell membranes.

Map of Hard Water Areas in Australia.

Compatibility Agents.

• You use compatibility agents to avoid issues with chemical mixes. An example of this is the spray adjuvant Fix-it Tank Mix®.

Here is a method for a  “jar test” to find out the stability of a mixture. Always remember to wear personal protective equipment (PPE) when you handle chemicals.

You will need a 1L or bigger glass jar. The key point to note is that how well a tank mix works, depends on how well the products mix.

Doing a Jar Test.

1. Measure 500 ml of water into the glass jar. You want to use the same water source you use in the tank.
2. The aim is to mirror on a small scale, what happens in your tank. Add the products you want to use in the same proportions.
3. You need to do this one at a time, as per the label. If the rate is 10 Kg per 400 L then add 12.5 g to 500 ml of water.
4. If there is no order to mix on the label, then add them in the order below.
5. Each time you add a product, make sure you stir it well until you add the next one.

• • Add your compatibility agent, buffer, or defoamer.
  • Add wettable powders, dry flowables, and water-dispersible granules.
  • Next add flowables, liquids, and micro-encapsulated products.
  • Next add solutions and soluble powders.
  • Then add any adjuvants that remain. This includes surfactants or crop oils.
  • Add any emulsifiable concentrates.
  • Liquid UAN.

4. Shake the jar and leave it for at least 15 minutes. The mixture is not compatible if:

• A scum forms on the surface.
• The mix separates out.
• Solids form and then settle to the bottom.
• Clumps or gels form.
• It gives off heat or a smell. If the jar feels warm to the touch and/or there is a strong smell don’t use the mix.

If issues occur, this mix is not compatible and you should throw it away.

How to Choose A Spray Adjuvant.

• Read the product label. Many labels list what to use, and in some cases these details are under the “Directions for Use” section.
• Use the active ingredient content to calculate the cost.
• Use a brand that has data to support its claims.
• Only use formulated products. If you don’t it may affect the chemical performance. So don’t use washing up liquid.
• If it makes claims that sound to good to be true, these probably are.
• You don’t always have to use an adjuvant.
• Make sure that your equipment is set up properly.

Spray Adjuvants For Turf Products.

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