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By Dr Brian de Villiers
February 2026
Incompatible tank mixtures have become more prevalent over the last decade. One of the major reasons for this is water volume. Growers have decreased volume, thanks mainly to modern spray equipment. However, lower water volume also decreases the margin of error when making up tank mixtures. This is because tank mixture ingredients
applied on a per area basis are present at much higher concentrations of the spray solution. Therefore, the chance for chemical and physical reactions increases. However, water quality also plays a major role. It is astonishing that some growers apply high-risk tank mixtures with no issues, while others experience incompatibility with the same mixtures.
Incompatibility
Incompatibility is a huge problem because it causes flocculation and other reactions in the sprayer. This costs growers precious time because sprayers must be cleaned in order for the spray mixture to be re-applied. It also leads to financial losses due to lost productivity and chemical wastage. The reason why certain growers get away with suspect tank mixtures is often because of the spray solution pH. Acidic crop protection products (CPPs), foliar nutrients and adjuvants decrease the pH of certain water sources much more than others, thereby limiting the solubility of one or more of the tank mixture components. An insoluble product then reacts with other products in the tank mixture during agitation, forming solid particles that block sieves and nozzles. These problematic water sources are often soft, with low ion levels. This proves that all water qualities have challenges and that one should be aware of the potential risks associated with spray water.
Reduced solubility
An additional challenge with incompatibility caused by insolubility is that it is often so subtle that it cannot be detected easily. Even if a jar test shows no signs of incompatibility, there could still be a solubility issue, causing inefficacy or even crop damage. The incompatible substances within the tank mixture may not block sieves and nozzles but could cause problems to occur later in the process, while the droplet is drying on the leaf. This could also lead to a delayed and prolonged absorption process, giving the spray droplet more time to scorch the crop. Therefore, it is important to only use registered tank mixtures that have a track record for efficacy and compatibility. It is
also important to know the specific challenges associated with the particular water source, and to only apply ultra-acidic products strictly according to label recommendations.
Villa’s stance
All forms of incompatibility, whether evident or subtle, could have a devastating influence
on efficacy. It is important to have a thorough knowledge of water quality in your area and to avoid high-risk tank mixtures. Just because a CPP combination can be successfully applied with water from one source, does not necessarily mean that it will be the case for all water sources. Contact your Villa agronomist for more information about adjuvants and water quality.
