AGROCHEMICALS
In some cases, the addition of an extra super-spreader into a formulation can destabilise pesticide emulsion or suspensions. These practical factors combined with potential future regulatory restrictions are driving many companies to review their usage of this class of additive.
Uptake enhancers
Uptake enhancers can increase the rate and quantity of active taken into a leaf. They can be highly effective for systemic actives that must cross the leaf cuticle to provide performance, as once the active is within the leaf it is not affected by rainfall.
They are unsuitable for contact MoAs and, even for systemic products, they must often be carefully selected to match the active ingredient, so they are far from a catch-all solution. Where applicable though, uptake enhancers are often an excellent choice for boosting performance regardless of whether a rain event occurs and maintaining that performance if it does rain.
Stickers
Stickers are chemicals that will form a film on the leaf surface that is resistant to environmental factors such as rain, irrigation and humidity. These are often the most versatile in terms of compatibility with a wide range of actives.
However, many of the highperformance polymers used as stickers will fall in scope of the upcoming synthetic polymer microparticle legislation in the EU and many agrochemical companies are therefore looking to move away from them. Although this legislation does not apply to all territories, numerous formulations are used across many regions and therefore meeting requirements for sale into the EU is often desirable.
Measuring performance
Measuring any adjuvant performance is broadly split into screening tools and biological testing. The former are quicker, cheaper and often easier, while the latter is more directly indicative of final performance. Once performance has been established in the screening stage, candidates will be advanced to more expensive and time consuming but real-world relevant glasshouse studies and finally full-scale field trials.
Given the importance of rainfastness performance for delivering efficacy from products, it is important to be able to measure and compare performance across different formulations in a quick and consistent manner. As with additive choice, this will vary with the active and MoA in question.
For uptake enhancement screening tools like Franz cell studies may be used, while for wetting agents a combination of physical chemistry tests can be used to characterise spreading, wetting and drying performance. For the final class, stickers, it is often required to simulate the full application, drying
Figure 2- Example of rainfastness data produced using glass slide screening method and rain event sequence to observe relative performance.
Sticker MoAs
Simulating the full rainfastness cycle of a sticker-based formulation at lab scale can take a number of different forms, each with their own strengths and limitations, but this outline will focus on the method Croda uses in internal product performance evaluation screenings.
For this method, the goal is to be as reproducible as possible and we have therefore made some concessions on real-world authenticity, such as using synthetic substrates instead of leaves, and pipettes to control application rather than sprays. For the lab method of measurement, we use a variety of industry relevant formulations spanning herbicides, insecticides and fungicides and measure their performance with built-in and tank-mix adjuvants.
The formulations are diluted to their standard in-use concentrations as per their label, then a sample dropped onto a test slide. These are microscope slides that have been coated in a synthetic coating to simulate a hydrophobic leaf surface in a consistently flat and repeatable way. These slides are then left to dry in a temperature and humidity controlled environment.
The slides are mounted at 45 ° in a custom rig, with a water outlet mounted above the deposit. A peristaltic pump is used to deliver continuous drops of deionised water directly to the slide above the deposit, which is allowed to run down across the deposit to simulate a rain event.
The deposit is imaged using a USB microscope throughout the test, with one image taken every ten seconds for five minutes. The images are then analysed using custom software that measures the percentage of the deposit remaining in each image( Figure 1).
By plotting the time against the remaining deposit, we can observe the relative rainfastness performance at each time point and compare the properties of different additives
JAN / FEB 2026 SPECCHEMONLINE. COM
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