Skip to content
By Dr Brian de Villiers
January 2024
Crop protection products (CPPs) are mixed with water to be applied evenly over an area. However, water has chemical and physical properties that can be detrimental to CPP efficacy. Six major adjuvant groups are used worldwide, namely buffers, salt adjuvants, deposition agents, surfactants, oils, and stickers. It is hard to believe that four adjuvant groups are fully or partially involved in addressing water quality. Therefore, it is always important to use the most effective adjuvants in addressing spray water. Unfortunately, growers often disregard the importance of spray water, resulting in incorrect adjuvant use and poor control.
Cations and pH
All water sources contain some dissolved cations and have a specific pH. Salt adjuvants are used widely with certain post-emergence herbicides to neutralise antagonistic cations and to increase efficacy. After so many years of ammonium sulphate use, we still believe it is the most effective salt adjuvant for our herbicides. We recommend using these adjuvants as a standard practice when the label recommends it. South Africa’s water usually has an alkaline pH, often between 7 and 9. Unfortunately, alkaline water speeds up the degradation process of insecticides and it may also decrease the efficacy of some other products. We, therefore, encourage using buffers with all our insecticides where the label specifically recommends acidification. Only use the recommended buffers at the label rate to ensure the correct pH, depending on water buffering capacity. Remember, a small difference on the pH scale means a major difference in acidity.
Surface Tension
One of the definitions of surface tension is the ability of a liquid to act as if enclosed in an elastic layer. Unfortunately, water has a high surface tension, so the spray droplets are prone to droplet bounce on impact with the leaf. This decreases the retention and deposition of spray droplets and has a direct negative impact on control. Therefore, we use surfactants or oil adjuvants to decrease the surface tension of the spray solution and reduce droplet bounce. However, only use the adjuvant on the CPP label as products on the market differ vastly in their ability to reduce surface tension. The reduction of surface tension also influences spreading after retaining the droplet. Although surfactants and oils have many other benefits, they also play a very important role in the physical aspects of water quality.
Villa’s stance
Water quality is one of the most limiting factors for CPPs. It’s not only the water’s chemical properties that are important, but the surface tension also plays a major role. This is the reason why four adjuvant groups are fully or partially involved in solving water quality problems. Before replacing these registered adjuvants with similar products on the market, first consider the impact. If not addressing water quality fully with the correct adjuvant, it will result in poor control, a possible re-application and increased pest and weed infestation. Contact your Villa marketing advisor for more information about adjuvants and water quality.