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.
• Increase spray retention on the plant surface to improve foliar uptake.

What are Spray Tank Adjuvants?

Spray and herbicide adjuvants are compounds that you add to a spray tank to improve how well a chemical mixes, improve its application or how well it works.

Some formulations of glyphosate such as (Rapid Fire) include a spray adjuvant. In other cases there are stand-alone herbicide adjuvants that you add to a spray tank. The use of spray adjuvants is common in Sydney and Canberra due to the unique climates that turf managers face.

For example:

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

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

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

Do spray Tank 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. 

Zawierucha in 1998: 

• Quinclorac with no adjuvant does not control Sowthistle;
• All adjuvants give better control with Quinclorac except for a modified polysiloxane.

Woznica, Z et al 2003: 

• Quinclorac works nearly twice as well on Green Foxtail when you increase the spray pH from 2.6 to 7.3.

The Benefits of Spray Adjuvants:

• They help products mix better.
• Spray adjuvants improve the contact between a pesticide and the target.
• Water conditioners alter the water chemistry to improve how well a chemical works.
• Herbicide adjuvants increase the rate at which chemicals move through the leaves and stomata.
• Spray adjuvants increase chemical safety by increasing its selectivity.
• Spray adjuvants reduce the chemical rate by 5 to 10 times and so reduce costs. Spray adjuvants cost a lot less than turf chemicals. A USA study shows that the use of spray adjuvants reduces costs by up to 40%.

In many cases use of a spray adjuvant improves how well a turf chemical works. The graph below shows how the use of a spray tank adjuvant improves the performance of Azoxystrobin.

Thanks to the USDA Agricultural Research Service for these videos, that show how the right spray tank adjuvant improves chemical movement into a leaf.

The Negatives of Spray Adjuvants.

Spray adjuvants can also have negative effects.

• In some cases they can reduce how well a chemical works. For example a water conditioner or pH buffer doesn’t always improve the results you get.
• Besides this they can also increase the life of chemicals so it takes longer for them to breakdown, and they persist longer in the environment.
• Some spray adjuvants are even dangerous themselves, which is the case with the carrier in many Glyphosate formulations.

In fact there is no perfect spray adjuvant that makes all turf chemicals perform better in all situations.

History of Spray Adjuvants.

Below is the 2013 APVMA data for chemical use by dollar value, vs the 2020-21 figures. In short, both the number of products, and the value of spray adjuvant sales show huge increases.

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

However, over time there has been a significant amount of investment which has lead to major advances in understanding how these work, and the results from their use.

How to Use Spray Adjuvants.

Spray adjuvants have several modes of action. They increase the retention, spread, and movement of chemicals into plants, and also have the ability to effect spray droplet size, reduce foam or even alter the water pH. 

Activator Spray Adjuvants.

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

Spray Modifiers.

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

Utility Spray Tank Adjuvants.

Ultility adjuvants include products like anti foam or defoamers, spray buffers, and water conditioners. These increase the range of 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, and they reduce a spray solutions surface tension and how it behaves. You often find these in use as herbicide adjuvants for weed sprays.

The reason for this is that if you lower the surface tension of water, the spray solution spreads out over the leaf, and does not bead on the surface.

The surface tension of water is 72 dynes/cm, and surfactants reduce the surface tension of a spray down to 20 to 30 dynes/cm. This reduction in surface tension allows greater uptake as the spray stays in contact with the leaf surface for longer. This is why you use a non ionic surfactant for herbicides like Duke herbicide, Recondo herbicide or Tribute Selective herbicide.

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, and so make 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 crystallization and
• Increase the drying time 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 what is called the hydrophilic (water-soluble) and lipophilic (oil soluble) components of a spray adjuvant is called the Hydrophillic –Lipophilic Balance (HLB).

When you use a spray adjuvant, 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. In contrast 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), and
• Cationic surfactants (positive charge).

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

Non-ionic Surfactants.

Non ionic surfactants are the most common of these. As well as being hydrophilic (water-loving), 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.

Nonionic surfactants reduce the surface tension of a spray solution, and also change the nature of a leaf surface by impacting the leaf cuticle.

Organosiloxanes, like Proforce Scrubwet, when you use these as herbicide adjuvants, 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 these also influence the amount of chemical that passes through the cuticle.

This super spreading property makes them nearly impossible to wash off a leaf surface even if it rains after use.

Work shows that an organosilicone adjuvant significantly improves the uptake of phosphorous acid into Pinus radiata needles and improves its performance against Phytophthora species. Ongoing work is looking at the use of these to help with the control of adult stem weevil.

Oils.

The three types of oil-based spray adjuvants are crop oils, crop oil concentrates, and methylated seed oils. These are popular as a herbicide surfactants because they increase the movement of a chemical spray into a plant, and reduce surface tension.

Crop Oils.

These are also known as petroleum oils, do not contain any vegetable oil, and contain a maximum of 5% surfactant. Use of crop oils as spray adjuvants, promotes the movement of a chemical spray 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 work well as herbicide adjuvants as they help make some of the less-soluble herbicides more soluble in water.

This means that they are often used as herbicide surfactants to target grass weeds like Summer Grass. Good examples are Hasten spray adjuvant and Banjo spray adjuvant which are a combination of vegetable oil and nonionic surfactant.

Methylated Seed Oils (MSOs).

These are oil-based surfactants, and can cause leaf burn and phytotoxicity. A good example in this group of spray adjuvants is Voltage MSO. These are the most active of the herbicide adjuvants, and work best on larger or drought-stressed weeds that are not growing.

This type of herbicide surfactant has the following benefits:

• When you use this type of spray adjuvant they increase the drying time on a leaf surface. This increases the time for herbicide uptake.
• These herbicide adjuvants solubilize leaf waxes, and improve chemical penetration of a leaf.
• They improve the control of larger weeds.
• You get better control of weeds under stress or that are not growing and
• These herbicide adjuvants work well on hard-to-control weeds.

MSO’s improve the performance of Quinclorac to control Spurge or Summer grass. This happens because when you use an MSO with Quinclorac, it does two things:

• It enhances chemical movement into the leaf.
• MSO’s keep a chemical in solution rather than it crystalizing on the leaf surface.

Use of Nominee for winter grass control shows that treatments with an MSO spray adjuvant and a nonionic surfactant, needs 25 and 41% lower rates, in comparison to the normal rates without the use of a herbicide adjuvant.

Water Conditioners or Spray Buffers.

For the most part the ideal water pH for most turf chemicals is in the range of 4.0 to 6.5, and it is best between 5.5 to 6.5. One outlier to this are the Group 2 herbicides, which give better results at a pH of 7 or greater. The reason why most chemicals work better in the 4 to 6.5 pH range is due to alkaline hydrolysis.

Above a pH of 7, some turf chemicals tend to be prone to this such as iprodione-based fungicides like Voltar® 500SC. This has a half-life of 48 minutes at pH 7.

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, more consistent performance, and lower chemical use and labour costs. 

Water pH.

If you think water pH doesn’t effect you think again. Water quality changes through the year so you need to check it regularly. Generally speaking tap water in Australia is artificially increased to above pH 7.

So if you use this as your spray tank water in some cases you need to use a spray buffer. Do not however, 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 and you use town water, there are some great online water analysis tools available. Simply fill in your post code and it will give you a water analysis.

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.

Anti-foam reduces the build up of foam which is an issue in soft water areas like the ACT. Polydimethylsiloxane is the active in Foam-aid and both prevents foam while you mix but also removes foam that is already present.

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 an ability to reduce evaporation, and also greater UV stability. Bond adjuvant® or Octane® are examples of these.

Drift control agents reduce spray drift as they increase the spray droplet size. Droplets with a diameter of 150 microns or smaller tend to drift, and the use of drift control agents means you can better target your spray.

They increase the average droplet size by binding 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 listed on labels of products like Specticle herbicide and Numchuk Quad.

Modifying Spray Drop Size.

Wetting agents tend to reduce the spray drop size, while oil-based adjuvants tend to increase it. When you spray, consider the 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, and the aim is to use a specific-sized spray to get the best results. Drift occurs if droplets are too small. In contrast, if drops are too large they will run off the target.

Foam Markers and Colourants.

Foam markers are spray adjuvants that you use to see where you spray without having to use a colourant. This helps avoid overlap when you apply turf chemicals.

You use colourants such as Blue spray indicator as marker or indicator dyes to identify areas that you have already been sprayed. This is in contrast to turf pigments that are used 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 and you should always use these to clean a spray tank if it has been used with non selective herbicides like glyphosate or the sulfonylureas.

Ammonium Fertilizers.

You use Urea-ammonium nitrate (UAN), and ammonium sulphate (AMS) as spray tank adjuvants to reduce the negative effects of hard water. Fe, Zn, Mg, Na, K, and Ca react with herbicides like 2,4-D and glyphosate to form insoluble precipitates.

In hard water areas, you should consider always using crystalline or spray-grade ammonium sulphate as a herbicide adjuvant to stop the Ca form of glyphosate forming.

Don’t use granular or standard ammonium sulphate with glyphosate as these both contain impurities that will give poor results.

If you add crystalline ammonium sulphate as a herbicide adjuvant to a spray tank the temperature of the solution will drop. This what is called an endothermic reaction.

Because of this, be aware that in the Winter the drop in temperature makes the mixing of turf chemicals 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 Showing The Ammomium Sulphate Rate for Hard Water.

Turf is very efficient at taking up NH4 ions. This is because it is at the expense of H+ ions which are transferred to the outside of plant cells. This results in a drop in the pH. With the use of NH4 it increases herbicide uptake by creating a pH gradient across cell membranes.

Map of Hard Water Areas in Australia.

Compatibility Agents.

How often do you want to know if you can mix some ingredients and they are compatible? You use compatibility agents to avoid issues with chemical mixes. For example, the spray adjuvant Fix-it Tank Mix® does this.

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 turf chemicals.

Get 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 in a spray tank.

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 spray tank.
2. The aim is to mirror on a small scale what happens in your spray tank. Add the products you want to use in the same proportions, one at a time, as per the label. So if the rate is 10 Kg per 400L then add 12.5 g to 500 ml of water.
3. If there is no order for mixing on the label add them in the following order. Each time you add a product make sure you stir it well until you add the next one.

• • Add your compatibility, buffering, or defoaming agents.
  • Second, add wettable powders, dry flowables, and water-dispersible granules.
  • Third, add flowables, liquids, and microencapsulated products.
  • Next add solutions and soluble powders.
  • Then add the remaining adjuvants, such as surfactants or crop oils.
  • Add any emulsifiable concentrates; and finally add
  • 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 mixture separates.
• Solids form and 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 mixture.

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

How to Choose A Spray Adjuvant.

• First, make sure you read the product label as it’s there for a reason. Many turf chemicals list what adjuvant to use, and in some cases these details are under the “Directions for Use” section.
• Second, use the active ingredient content to calculate the actual cost.
• Third, use a brand with supporting data. Do not use anything other than a formulated product as it may impact on the chemical performance. So for those that use washing up liquid. Stop!
• Next, if it makes claims that sound to good to be true, they are!
• You don’t always have to add a spray adjuvant and
• Make sure that your equipment is set up properly.

Spray Adjuvants For Turf Products.

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