Follow Us:

Biologicals, without the blockages

Biologicals have emerged as key agricultural products for enhancing crop productivity and nurturing soil health. However, the path to harnessing their benefits isn’t always straightforward. Challenges arise, from compatibility issues to practical handling concerns, reminding us that while the principles may be natural, the execution demands careful attention to detail.

In this article, we delve into the issues that can arise when mixing various biological products and how to overcome them.

Fish-based organic fertiliser

Most commonly extracted using phosphoric acid. Phosphorus often reacts with soluble calcium to form insoluble calcium phosphate. Once this forms, it isn’t going anyway, no matter how much you rinse the system. So avoid calcium containing products when using fish-based fertilisers, or do a bucket test first.

The other issue with many organic fertilisers, including those based on fish, is that they are commonly suspensions, not soluble concentrates. As such, if left for a long period of time in the spray tank they may settle out and form a layer along the bottom of the tank. Therefore, do not store diluted product overnight. Storing diluted biologicals is also never advised because it will stimulate microbial growth and the additional problems that come from that if not precisely controlled.

Molasses-based organic fertilisers

When it comes to molasses it is the actual water you need to take care with. If you pour molasses quickly into very cold water it can sink to the bottom of the tank in one big solid lump! If that lump is sucked into a mixing pump it can cause a catastrophic failure. Therefore always add molasses slowly to any tank and agitate continuously. Alternatively, pre-dilute the molasses in some warm water before adding to the tank for further dilution to the spray concentration. 

Seaweed extracts

Confirm the pH first. Some are acidic, some neutral, but more commonly they are alkaline. If alkaline, avoid any product that will lower the pH and bring the carbohydrate (alginic acid etc) solids out of solution.

Always avoid mixing with chitosan. As chitosan is acidic and cationic (seaweed extracts are anionic); any mix of these two will result in something with the appearance of vomit! If this doesn’t happen, you are using poor quality seaweed extract and/or chitosan solution.

Humic and fulvic acid

Humic acid solutions are very often moderately alkaline. So avoid any acidic product that will bring the pH down. If this happens you will get a thick tar coating your filters.

We have seen a few cases recently of issues when tank mixing with citric acid. This has happened because farmers are now hearing that the efficacy of glyphosate (Roundup) can be increased by lowering the pH with citric acid. They are also hearing that the efficacy of glyphosate can be increased by the inclusion of humic or fulvic acids. So they have applied all three products to the spray tank and blockages have occurred. 


In addition to its use as a biostimulant and biofungicide, chitosan can also be used to remove contaminants from wastewater. Chitosan is used in waste water treatment because it binds to contaminants and takes them out of solution. So while removing bacteria, metal ions, and humic acid might be an advantage in that scenario, in a spray tank the opposite is true.

Chitosan can be tank mixed with a variety of conventional agrochemicals and biologicals, but you need to do your homework first, and always conduct a bucket test with the dilution ratios and water you plan on using. If you need a small sample to do a tank mix with, then please get in touch.

I always used to tell customers to never mix chitosan with silicon fertilisers, as these are alkaline and will also fall out of solution if mixed incorrectly. However, we have now developed a way of successfully tank mixing these products together by adjusting the pH of the solution after the addition of the silicon fertiliser. See our Fungicide Reduction Action Plan for more information.

Plant extracts

It really depends on the type of extract, the pH and the purification as to how these will tank mix. A single chemical extract will stand a far greater chance of tank mixing than a crude extract (such as a cold-press ‘juice’).  

One example is yucca extract that contains natural soaps (saponins), these work best at pH above neutral. So if mixed with acidic co-applied products their efficacy may be diminished. 

Amino acid biostimulants can also be derived from plant extracts (commonly from legumes). Other sources of amino acid biostimulants used in agriculture include fungal cultures, and the digestion of animal protein; particularly those sourced from pig’s blood, bird feathers, and fish waste. 

Amino acid biostimulants can have tank mixing issues with ALS inhibitor herbicides. This is because ALS inhibitor herbicides work by disrupting the synthesis of  amino acids in the weed. If you apply ample amino acids alongside the herbicide you could potentially negate the effect of the herbicide because the weed still has access to the amino acids that would otherwise be disrupted.


Nematodes are notorious for blocking filters and spray nozzles. Nematodes are animals that are small enough to be delivered in water as a spray to the leaf surface. However, being animals, they are far larger than microbial biologicals, or suspension fertiliser particles and as such standard fitting filters and nozzles will block if nematodes are run through them. As such, research the filters and nozzles for optimum nematode deliver, and factor in the cost of these if you do not have them in stock at present.

Nematodes are actually very close to being delivered by drone in the UK. The smaller volume applications or even dry applications that drones offer may suit nematode application better than conventional sprayers.


When it comes to using microbial biologicals the first, and most obvious, tank mixing issue is that they should never be mixed with conventional chemical fungicides / bactericides. These pesticides act as biocides and will kill the beneficial microbes ithey are tank mixed with. In addition, many insecticides and herbicides might also have antimicrobial activity, so it is always best to check with the manufacturer before combining with microbials in the tank.

Another consideration when using beneficial microbes is to the chlorine in tap water. While most farmers use water from tanks rather than tap water, a sizable proportion do use tap water; especially in periods of drought. If using tap water alongside microbials always add a dechlorinator first.

Fungal biologicals

Fungal biologicals include symbiotic mycorrhizae, free-living Trichoderma, and fungal biopesticides. Normally fungal biologicals are supplied from the manufacturers as either spores or ‘propagules’. Spores are usually <50 micron in diameter, so unless they have clumped together in the packet, they should fit through a spray filter. Propagules are far larger than spores and should be applied as a dry powder rather than suspended in water as they will block filters. 

This being said, spores are not always the best option for delivering fungi, especially mycorrhizae. This is because spores have less chance of forming a good connection with the plant due to having lower reserves of energy and nutrients to grow, find, and connect with a plant root. I would therefore recommend that for mycorrhizae dry propagules are applied to established plants by digging them into the soil around the root system, and spores are reserved for application as a seed coating (see this video for how to do this).

For fungal bio-pesticides spore form is usually the best (and only) option, and can be delivered in water-based foliar sprays easily if the instructions for use are carefully followed.

Yeasts are also fungi, but they are single-celled and each cell is very small (3-4 micron), so for foliar applications they can be treated as you would fungal spores.


Bacteria should tank mix fairly well as they are very small single cells, but you may still suffer compatibility issues with some agrochemicals if they have biocidal action and could kill the microbes. You will also need to study the best pressure and nozzle settings to best apply bacterial inoculants. 

Compost tea

Many compost tea enthusiasts ‘seed’ their brews with specific microbial inoculants. However, compost teas are not made in sterile conditions, and so other microbes will be present and will be cultured alongside. Some of these may be filamentous or conglomerate into biofilms. These may block filters if present in very high concentrations. 

If you are in any doubt about the tank mix compatibility of a biological product, simply give us a ring and we will be happy to discuss this with you. The field of biologicals is developing rapidly, so we will be updating this article regularly.

Finally, if you need any help sourcing any of the biologicals listed above, please email me;

Dr Russell Sharp

Leave a Reply

Your email address will not be published. Required fields are marked *