|Version 2||Date January 2020||Reference 26|
Multiple tank mixes are becoming increasingly prevalent, particularly for pre-plant and early post emergent applications where getting across large areas in a timely manner is critical.
Unfortunately water is often not a great carrier for agricultural chemicals as it is a charged polar molecule and variability in water temperature and quality can affect how well products dissolve into it. When the cost of product in a spray tank is considered, it pays to ensure that they are mixed correctly.
Most agricultural chemicals are formulated to be as emulisifiable as possible, but many contain elements that either do not dissolve well (wettable powders – WP’s and water dispersible granules – WDG’s), petroleum distillates (emulisifiable concentrates – EC’s) or just precipitate, as they are heavier than the water (fertilizers, powdered metals, etc). Care should be taken when using these, particularly when under time constraints.
This technote describes correct mixing techniques to optimise active ingredient activity by maintaining them in suspension in the spray tank during the entire spray operation. Adjuvants and compatibilisers such as N-Flow® play a major role in bonding the otherwise unmixable spray materials with water.
Some of the more common mixing issues can be avoided simply in three ways:
One of the most common causes of uneven application due to poor agitation lies with the spray applicator. Examples are:
Tank mixes with multiple components may overload the product specific surfactant systems and cause physical incompatibility. This can be observed as settling in the tank, thick paste residues on the tank bottom and filter blockages.
Incomplete dispersion or mixing will cause competition from components for the water to allow dissolution, dispersion and suspension to occur.
Incorrect order of addition and/or insufficient time between additions of each component means it is likely that product will settle in the tank. This settling will concentrate the active ingredients in the lower half of the tank.
|Image 1 & 2 : Modern spray equipment is designed for efficient coverage of large areas – however care should be taken with speed of tank filling and mixing (Source: SACOA)|
|Image 3 & 4 : Modern spray equipment is designed for efficient coverage of large areas – however care should be taken with speed of tank filling and mixing (Source: SACOA).|
This may lead to filter blockages and also has the potential to cause both under and overdosing during the application. This will give either limited control of target species or setback the progress of the crop.
Tank mixes of dispersed insoluble actives (flowables and granules) can have physical incompatibility when mixed with EC’s. Triazines can be a problem as there are big differences in quality and size of granules. If intending to use triazines in tank mix combination with other EC’s, only use a quality triazine product.
Tank mixes of glyphosate and flowables/granules may also be antagonistic without the use of water conditioning agents, such as Ammonium Sulphate or compatibilisers such as N-Flow®.
Products with low water solubility need to be added first!
Wettable Powders (WP’s)
These are the slowest to dissolve as they have a very large surface area to be wetted and are often based on hydrophobic bases such as clays – hence they should be added first. Oils in particular reduce the mixing ability of wettable powders as they cause coating.
Water Dispersible Granules (WDG’s) or Dry Flowables
These are similar to wettable powders in being difficult to dissolve. Due to their additional weight they tend to sink to the bottom of the tank – and hence require agitation to keep them suspended. Again contact with oils will reduce the ability to dissolve.
Flowables – are a slurry of wetted particles and hence are still susceptible to non-mixing with oils or emusifiable concentrates, particularly when added to low water volumes or cold water.
Soluble Liquids eg Emulsifiable Concentrates (EC’s)
These consist of active ingredients already dissolved in water and therefore only require dilution in the spray tank.
|Image 5 : Chemical batch mixer (Source: SACOA).|
|Image 6 : Glyphosate is inactivated in hard water (Source: SACOA).|
Each step should be separated by appropriate time and amounts of water.
Exercise caution when adding spray adjuvants (oils and wetters) to a tank mix through granulated product mixers (e.g. granni pots) by ensuring the water is vortexing (spinning) through the mixer.
Chemical mixers are designed to help mix dry flowables and wettable granules. Care must be taken when using this equipment to add wetters and oils to a tank mix. Small amounts of water can be trapped behind the tap or in the plumbing, so when the tap is opened, this small amount of water mixes with the large amount of oil, which will overload the surfactant package and cause the oil to separate. Often a ricotta cheese like substance can be seen floating on top of the tank.
If you have a problem, don’t panic and dump the mix, as many events are recoverable. Be prepared to spend the time and effort to resolve the issue. It may require the addition of other products, such as N-Flow® or an additional surfactant such as WETTA1000® to assist recovery.
If product has started to settle in the tank and possibly block filters, then stop recirculation, remove filters and then resume recirculation at the fastest rate possible. If severe settling has occurred, it may be necessary to use a high volume pump like a fire fighter.
Manual agitation of the solids may be required to assist initial movement of material through the recirculation piping. For mixtures of dry flowable/granules and water-soluble products, the addition of small amounts (200mls at a time) of extra surfactant, such as WETTA1000®, may be required to assist in the re- suspending process.
Once the products have been successfully re-suspended, apply with constant agitation. Thoroughly clean out the tank after use and before a new mix is attempted. If extra help is required contact your reseller or chemical company representative.
Finally, as prevention is always better than a cure, if unsure of tank mix combination, perform a jar test. The mix should not be attempted if the following is observed;
• Solid residues
• Separation of liquids, film on top of the liquids
• Heat generated
• Poached eggs on top
|Image 7: Granni pot mixing intake (Source: SACOA)|
|Image 8: Example of filter blockage and tank residues known as a reverse emulsion resulting from incorrect mixing procedure (Source: SACOA)|
Disclaimer and Copyright
This document should act as a guide only and no purchase or usage decisions should be made based on the information provided without obtaining independent, expert advice. SACOA and contributors do not necessarily recommend or endorse any products or manufacturers referred to. SACOA Pty Ltd will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information contained in this document. More information is available from SACOA via sacoa.com.au or 08 9386 7666, or by contacting your local reseller.
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