Adjuvants are materials added to crop protection products or agrochemicals to enhance the efficacy of active ingredients and improve the overall performance of the product.
These additives modify the properties of the spray solution, which improves the ability of the active ingredient to target, penetrate or protect the target organism. Adjuvants can be incorporated into a formulation (built-in / in-can adjuvant) or can be added separately into the spray tank alongside other agrochemical products (tank mix adjuvant).
Adjuvants can enhance product performance by:
This leads to:
Different types of adjuvants offer various benefits and advantages, which are achieved through five adjuvant processes:
Understanding Droplet Characteristics and Behaviour
Spray droplets that are too large may bounce off a leaf’s surface and not reach the intended target, but how large is too large and how can spray composition affect droplet retention and deposition?
To understand this, we have developed a method that can produce a single droplet, of an agriculturally relevant size. Our advanced high-speed camera and image analysis operating system then allows us to study the interactions between droplet size and velocity, surface properties and spray composition (including the addition of an adjuvant).
Our analysis shows that factors such as; the nature of the surface, the angle of impact, the size of the droplet and also the composition of the droplet, all have an influence on the spray droplet behaviour.
A video showcasing our capability can be seen here, demonstrating how a droplet behaves when it hits a surface and how changes in chemical and physical make-up of that droplet alter impact characteristics.
The formation and dynamics of spray droplets is important for ensuring products reach their intended target. Adjuvants can influence spray quality by reducing spray drift and wastage, allowing more of the product to reach the target. Therefore, use rates can potentially be reduced, leading to a better environmental profile and a potentially more cost effective solution. The type of adjuvant required is a drift reduction aid / spray drift mitigant.
Once a product has reached its intended target, it is important that the spray droplet does not bounce or run-off the leaf surface. Including a spray retention adjuvant dissipates the kinetic energy of the droplet during impact, meaning the likelihood of bounce or run-off is reduced.
Ideally, spray droplets should cover as much of the surface of a target as possible, distributing the active ingredient evenly. Wetting agents can be included to reduce surface tension and contact angle, leading to enhanced coverage.
After a period of time, water will start to evaporate from the spray droplet causing the active ingredient to precipitate out and form a deposit on the surface of the leaf. The formation and structure of this deposit can affect the performance of the active ingredient; for example, the active ingredient could be unevenly distributed on the surface. Adjuvants can influence the evaporation of water from the droplet, leading to a more homogeneous distribution of the deposit structure.
For systemic active ingredients to work, they need to be absorbed by the plant. The active ingredient is then able to circulate through the plant’s tissue killing the target organisms. Uptake enhancement adjuvants can improve penetration and uptake of active ingredients, resulting in increased bioavailability.
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