By Donald Lester
At any given time of the year, growers apply numerous products to their crops to keep them healthy and address nutritional deficiencies, disease or pests.
And to be as efficient as possible, they often combine pesticide or fertilizer products into one nutrient tank to apply in one hit rather than have several separate foliar or soil applications.
But, with each product having its own chemical makeup (whether organic or conventional) sometimes the mixing of products can have negative side effects or render the products useless. Which we agree actually increases costs as the product is wasted and plants may be harmed.
Just as the doctor tells you some medications are incompatible in humans, so it is for plants, but fear not – we’re here to help!
How To Spot a Chemical Incompatibility
There are a few visual clues that chemicals may be incompatible:
- Cloudiness in the mixture or a change in the texture
- Precipitation or settling of solids in the tank
- Noxious or toxic fumes coming from the mix
- Heat, fire or worse, an explosion
- Formation of solids or films inside tanks
- Plant phytotoxicity (i.e. burning) once the mixture is applied.
If a mix separates or settles, or becomes cloudy it becomes insoluble and unavailable to the plant.
Apart from losing efficacy on your crops, these mixtures can have negative effects on your equipment too. The settlement clogs dripper lines, it plugs filters and can affect your pump which wastes time in fixing and cleaning equipment.
Settling or sedimentation could be from a chemical reaction, or it can be caused by oversaturation. This is where no chemical reaction takes place but rather you simply are trying to mix too much of one chemical into another, and it’s ‘full’ and has not got any more room. Just like mixing salt in water, there is a limit to how much salt will dissolve. After we reach the saturation point any salt added will remain as sediment at the bottom of the jar.
Running out of ‘room’ in a mix can often be overcome by mixing the first product in a large volume of water and then adding the second product afterwards.
The temperature of the liquid has an impact too, warmer fluids can dissolve more, cooler fluids don’t.
How Do You Avoid Incompatibilities?
The first step is to always read the label, Product Information sheets and the Material Safety Data Sheet. It will list the main known incompatibilities, however, labels are small and literally are not able to fit large amounts of information, so if it is a new product you are using, check all information available. Manufacturers test likely mixes people will attempt, they obviously cannot test for every possible combination with every other product on the market, so that is where you need to also use your eyes to visually inspect the mix for obvious issues.
Do a Jar Test First
Don’t risk having to dump a whole tank of the product if you find out too late that it is incompatible. Do a small test first in a jar, aptly dubbed the ‘jar test’. Make sure you use a clean glass jar (not metal), mix the products in concentrated form – so any incompatibilities will happen right away.
Generally speaking, you can expect a reaction in the jar test if the two or more products have drastically different pH values (a difference of at least two pH units). You can find the pH values of the products on their Material Safety Data Sheets (MSDS). These forms are available from the manufacturer and are usually posted on their websites too.
Ensuring the pH of the water you use for dilution in near 7.0 is a good way to maximise compatibility. Sometimes incompatibilities can be improved by changing the water pH with an acidifier or conditioner first. Get the water pH right first, don’t try to adjust it once you’ve already started mixing.
There are various agents you can use to maximise or enhance compatibility. Whether you want to add a buffering or conditioning agent, a wetting or spreading agent, this is something that definitely needs to be discussed with someone who can guide you accurately on the chemical uses and compatibility.
Clean Your Tank
It seems redundant to say but make sure you start with a clean tank. Even a minor amount of chemical residue can interfere with a tank mix.
Mix in the Right Order
Some mixes need to be added in a certain sequence. Sometimes this will be noted on the label, but if you are in any doubt contact the manufacturer who will be able to guide you. Oftentimes this type of advice needs to come from a chemist or specialist, so your retailer may not have the answers. Don’t hesitate to reach out to the manufacturer.
Apply in a Timely Manner
Once a product is mixed, use it as soon as possible. Don’t let mixes sit around for days to degrade. This is especially important with biological mixes, the organisms are activated with water and need to find a food source (be applied) immediately to thrive, delaying for days will render them less effective.
Also important to note, once a negative reaction occurs, you cannot undo it. You need to start again. This is why testing in small amounts can save you a lot of time and money!