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By Dr Brian de Villiers
April 2025
Crop protection products (CPPs) are registered at a rate capable of controlling the disease, pest or weed. If the rate is decreased, the control will be impacted, and the consequences will be severe. The same principle applies to adjuvants. Adjuvants are used to enable CPPs to reach more of their potential. If an incorrect or too little adjuvant is used, the CPP will not reach its potential, and the control will be poor. One may get away with a low adjuvant rate when conditions are perfect, but the result of this error will become evident when conditions are marginal. It is important to ensure that the adjuvant you use is effective under all conditions and with all water sources. Ammonium
sulphate adjuvants will serve as an example to illustrate this.
Cation antagonism
An effective water conditioner should be used at a rate that negates the antagonism from at least calcium, magnesium, sodium, and potassium in spray water. Fortunately, the sulphate anion of ammonium sulphate can handle all four these cations, and it is recommended at a high enough rate. One must keep in mind that if spray water contains 1000 mg/ℓ of these four cations combined, there is 100 g antagonistic cations in every 100 litres of spray water. Therefore, you will need a high enough rate of water conditioner to neutralise these cations. Much research has been done on the efficacy of ammonium sulphate, so the Villa label rate will neutralise all these cations effectively to
ensure optimal weed control. This is why Villa is adamant about ammonium sulphate use, because the inability to address one of these cations, could result in ineffective weed control.
Other benefits
It is important to realise that ammonium sulphate has two other benefits, besides neutralising antagonistic cations. The first is that some of the Villa ammonium sulphate adjuvants are registered to overcome the antagonism of phenoxy herbicides on glyphosate. This is extremely important because these mixtures are popular, therefore it is crucial that the efficacy is not affected. Secondly, the role of the ammonium cation is also often underestimated. It plays a vital role in the absorption process, to improve efficacy of all applications. This also includes cases where cation antagonism is not a problem. Therefore, ammonium sulphate is not just a water conditioner. It also plays a vital role to reduce the antagonism of certain herbicides, and it helps with the absorption process. It is an indispensable adjuvant with the Villa herbicides.
Villa’s stance
Only Villa adjuvants are suitable for use with our herbicides when water conditioning is recommended. This standpoint is backed up by a significant body of international and local scientific research and technical expertise. Ammonium sulphate adjuvants help these herbicides to reach their true potential with all water sources and some tank mixtures. The only exception is muddy water, because water conditioners are not capable of dealing with this adequately. Contact your Villa agronomist for more information about adjuvants and water quality.
