Tank mixing hints and tips

It’s not just what you put in the spray tank that matters. Tank mixing has to be done correctly to make spraying safe and effective.

We frequently go out with complex tank mixes that include numerous products. To complicate matters, many new chemicals with formulations still being refined are entering the market, which means they may not readily mix in a way that older, more refined formulations do.

In all circumstances, the tank should be filled three-quarters with water before adding any chemical. This reduces the likelihood of collision of chemical particles. In other words, you are increasing the number of water molecules between the different chemical molecules.

If using ‘hard’ water, meaning water high in calcium (Ca) or magnesium (Mg) such as bore water, a water conditioner is required. This is because the Ca and Mg could bind to chemical molecules, causing blockages in the boom. The most common water conditioner is ammonium. When added to the tank prior to chemical, the Ca and Mg molecules bind to the sulphate, leaving the ammonium in suspension.

Ammonium, a form of nitrogen, can then aid the plant’s absorption of the chemical because it recognises the nitrogen attached to the chemical as a required macro-nutrient. This can increase chemical efficacy, particularly in adverse conditions (such as water or heat-stressed plants).

Alternatively, when using chemical formulations that do not readily disperse, the addition of wetters (detergents) can help to increase dilution of the product. Again, this helps to distance chemical molecules within the spray tank by increasing the number of water molecules between them.

Order is important

Chemicals can then be added. The correct mixing order  is illustrated below but always refer to product labels.

The tank should be constantly agitated during mixing to keep all products in dispersion (i.e. avoid products settling to the bottom of the tank).

Make sure you allow adequate time for full dispersion before adding the next product. Again, this is to increase the number of water molecules between chemical molecules to reduce the chances of collision, which is when chemicals can bind and cause blockages and other issues.

Note: always refer to product labels for specific mixing orders.

Elders has prepared a sheet with tips about spray drift awareness and correct mixing order.
Why not download a copy and pin it somewhere handy in your chemical shed!

The jar test for chemical compatibility

If unsure of chemical compatibility, a jar test can be an effective measure. First, ensure you are well protected from fumes or chemical contact with your skin or face with the correct personal protective equipment.

Then, simply add the same ratio of water and chemical to a jar (using the correct mixing order), before leaving the jar to sit overnight.

The solution can then be observed to identify any potential incompatibilities before mixing large batches. This is a common method used by chemical companies when releasing new products.

Once all products have been added to the tank, check the pH of the overall tank mix. Leave this as the last step because the addition of each chemical will impact the final pH. The ideal pH for plant uptake is between 4.5 to 5.8 (in calcium chloride) and can be changed using wetting agents, such as LI700, if necessary.

Filters and contaminants

Filter size can also affect spray efficacy is filter size. If running filters that are too fine, product may be ‘stripped’ from the solution potentially resulting in the application of sub-lethal chemical rates. This is partially important when using suspension concentrate products (SU’s).

It is important to decontaminate the boom between different crop types to achieve the best possible crop safety. Remember that oils can pick up residual chemical the lines – in other words the oil particles are able to remove residual chemical from the boom spray more effectively than water, sometimes resulting in bleaching and other herbicide damage to susceptible crops.

View the range of crop protection chemicals and fertilisers available at your local Elders store.