The addition of appropriate adjuvants in the spray tank is currently a key factor in improving the efficiency of any defensive application, thus increasing the performance of the product of interest and surprise, losses and risks in the process.
Technically, there are two main ways in which adjuvants can improve crop protection product performance. The first is to increase the amount of active ingredient that reaches the target, the second is to help in the process of its absorption. Thus acting in the stages of retention, dissemination, penetration and, finally, translocation in plant tissues.
Each adjuvant has specific properties that obey each type of application, aiming at desiccation (pre-harvest and planting) some characteristics become more important:
1 - Drop protection: maintains the size and weight of the drop that is produced by the nozzles until it reaches the target. It avoids losses, either by dragging caused by wind (drift) or even by evaporation, and improves absorption by increasing the average life of the droplet on the surface of the leaf.
Drop protection slows down two critical spray processes: dispersion and evaporation. Under hot, dry conditions, evaporation of droplets can occur rapidly forming crystals from the chemical residues that did not evaporate. In spraying, the waste is blown away from its destination by the wind, causing dispersion. When it occurs on the leaf surface, absorption is delayed or ceases completely. By increasing certain adjuvants in the spray solution, the droplet undergoes the evaporation process more slowly, allowing the plants to absorb and metabolize more active ingredients.
2 - Coverage: is the part of the surface of the target area covered by the crop protection product. Water, which is the main constituent of spray solutions, has a high surface tension (force exerted on fluid surfaces). And, in turn, the leaf is covered with a layer of wax, which makes it difficult to spread and retain the product on its surface, directly influencing its effectiveness.
The use of adjuvants in spray solutions increases the area wetted by the droplet on both sides of the leaves, due to their effect on the interaction between the droplet and leaf surface, decreasing the contact angle. The droplet should form a smaller contact angle, without causing overspreading that would facilitate evaporation.
Translocation: is the movement of the chemical compound within the plant, that is, the movement from the site of deposition of the pesticide to the rest of the plant tissues. The addition of certain adjuvants to the spray mixture has been shown to improve the permeability of the herbicide active ingredient, leading to greater cuticular penetration, stomatal infiltration and subsequently better translocation.
When we talk about desiccation, the key point is to make the herbicide translocate throughout the plant, making it reach mainly the roots of the plant. As we can see in Figure 3, the arrows show the place where the solution was applied, in A it was just the herbicide, and in B the herbicide plus the adjuvant. It can be seen that in the plant on the right (B) there was a greater translocation of the herbicide, both in the aerial part and in the root. In addition, today there are already on the market some adjuvants that have additives, which help the plant in the chemical translocation process, accelerating the desiccation process and reducing the regrowth of weeds.
It is worth remembering that for the performance of the phytosanitary product, factors such as the target to be achieved; the characteristics of the product used; the equipment; the time of application; and environmental conditions will not be acting in isolation, being responsible for the effectiveness or ineffectiveness of the application. For more information, contact a 3tentos consultant.
