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By Brian de Villiers
June 2024
Adjuvants are often omitted or replaced with an unregistered product without any negative consequences. Growers then assume that adjuvants are not important or that unregistered products can be used. This has led to a perception that adjuvants are snake oils and don’t really contribute to efficacy. It may be possible to get away with these malpractices under optimal conditions because there is not much for the adjuvant to fix. However, these practices are exposed under marginal conditions when the crop protection product (CPP) efficacy is much lower. In the ensuing discussion, water quality and humidity will be discussed as examples.
Water quality
Buffers and salt adjuvants are used to address water quality. Buffers manipulate the pH of water to meet the requirements of insecticides and other pH sensitive CPPs. Salt adjuvants complex antagonistic cations and increase the efficacy of cation sensitive herbicides such as glyphosate and clethodim. When the water quality is good, the effect of these adjuvants is reduced because there is little room for improvement. This is when unregistered adjuvants could be just as effective as the the registered product. The CPP applied without an adjuvant will probably also give acceptable control. However, when these unregistered practices are repeated when the water quality is poor, it will result in unacceptable pest or weed control. Poor water quality will expose incorrect adjuvant choice!
Humidity
Many CPPs are influenced by humidity. The efficacy of glyphosate is reduced by low humidity conditions, and it benefits from the use of certain types of humectants. When humidity conditions are optimal, an adjuvant with an incorrect type of humectant, or a product with too little humectant, may be just as effective as the registered option. The reason being that the humidity is high enough to achieve optimal absorption of glyphosate, regardless of the type or rate of humectant. However, under low humidity conditions, the incorrect humectant or a product applied at a reduced rate will be exposed by poor efficacy. Incorrect humectants under low humidity conditions may even slow down the absorption rate to the extent that the glyphosate scorches the leaf surface and causes crop damage.
Villa’s stance
Adjuvant choice is crucial to ensure adequate efficacy under all conditions. However, the difference between adjuvants is always exposed under poor conditions, where the margin for error is much less. Only use the adjuvant that is recommended on the CPP label. Failure to use this product will result in poor weed, pest, or disease control, especially when conditions are marginal. If this product is unavailable, contact the CPP registration holder for a registered and suitable alternative. Contact your Villa agronomist for more information about adjuvants and water quality.
