Adjuvants and Weed Management in Brazil

“We found out that 100% of pesticide applications are made with adjuvants, the problem is that the sprayed adjuvant is often not the right one.”

Anderson Luis Nunes is an agronomist, PhD in plant sciences and professor at the Federal Institute of Rio Grande do Sul State, where he leads the Ecophysiology and Weed Management Group.

adjuvants and weed

Anderson Luis Nunes, professor at the Federal Institute of Rio Grande do Sul State.

Weed management gets more and more complicated with each passing harvest. The banning of paraquat made the scenario more complex, especially when it comes to controlling narrow-leaf weeds.

We await new technologies and use them as soon as they become available, with the aim of mitigating yield reduction caused by weeds. However, often we forget the good old control practices. One of these control practices is the correct use of adjuvants.

In the current scenario of management of weeds that are difficult to control, the use of the correct adjuvant allows an increase in herbicide performance over the unwanted plant. We verified that 100% of pesticide applications are made with adjuvants, the problem is that often the adjuvant used is not adequate. The first issue is that adjuvants are not all the same.

Mineral or vegetable oil is not the same thing as a surfactant, although both are adjuvants. Adjuvant is any type of substance, without herbicidal effect, which, added to the spraying solution, increases the effectiveness of the application.

Every surfactant is an adjuvant, but not every adjuvant is a surfactant. There are herbicides in which the package requests addition of surfactants, while others require addition of oils.

When we believe that adjuvants are all the same, we start adding oil instead of surfactant or vice versa. In figure 1, we can see that the Quizalofop herbicide has high control of weeds when used in combination with oils, but its control is reduced when we use surfactants. The opposite happens with Glyphosate.

adjuvants and weed

Incorrect use of adjuvants becomes a problem mainly in the scenario of weeds that are more difficult to control, where herbicide application occurs outside the ideal control period and/or when environmental conditions are not suitable for herbicide spraying.

Addition of the correct adjuvant will increase the herbicide’s effectiveness. Part of the problem is that there is no rule on when to use oil or surfactant. It varies from herbicide to herbicide. The information should always be consulted in the product leaflet.

There are herbicides that do not require the addition of adjuvants, as the most appropriate adjuvant has already been added during the manufacturing process. Currently, type of situation is happening more, because in addition to being a market differentiator, the manufacturing industry better guarantees the efficiency of the product.

In figure 2, we can see how quickly the new clethodim formulation controls ryegrass plants, compared to the conventional formulation, where the addition of the adjuvant is necessary at the time of preparation of the mixture. In the two images, the only factor that varies is the type of adjuvant, since the amount of the active ingredient (clethodim) is the same.

Still, there are other types of adjuvants besides oils and surfactants, such as antifoams and pH reducers. Reducers are an important tool, as studies show that practically all water used for spraying pesticides in the Brazilian States of Rio Grande do Sul and Santa Catarina, for example, has a pH above the recommended level.

Also, pH reducers are particularly important in applications where the herbicides glyphosate, 2,4-D and some herbicides aimed at grass plants are involved. In figure 3, it can be seen that reducing the pH of the mixture from 6.8 to 5.0 causes 1 liter of glyphosate at pH 5.0 to have the same level of control as 2 liters of glyphosate at pH 6.8.

It is necessary to raise the awareness of technicians and farmers about the use of the correct adjuvant. Herbicides will have better performance against weeds that are difficult to control.













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