The science & significance of rainfastness adjuvants in agriculture
Ryan McDonald, applications team leader, and Sean Rouse, R & T specialist, at Croda share their insights into what rainfastness adjuvants are and why they are important to the agrochemical industry
In the ever-evolving world of agriculture, increasing demand for both food and renewable feedstocks, along with increasingly unpredictable weather patterns, fuels the drive for both higher performance and more weather-resistant formulations. Alongside these is the added challenge of increasingly restrictive regulations that reduce the size of the toolbox available to today’ s formulators.
A key area where all these factors come together is rainfall, which has the potential to wash away freshly applied herbicides, fungicides and insecticides before they can provide any protection to the plant. A key tool available to reduce the impact of rainfall on the performance of the formulation is the addition of‘ rainfastness additives’.
Rainfastness refers to a plant protection product’ s ability to maintain performance after exposure to rain or irrigation. This can be especially important in areas of high humidity or frequent rainfall, where timing applications around rainfall events is impractical.
Boosting the rainfastness of a formulation can allow farmers to protect the health of their crop while also reducing costs, emissions and environmental impact. It also reduces waste, allowing more of the active ingredient to reach the target, thus reducing the need for reapplications throughout the growing period and in some cases reducing the quantity of pesticide that ends up in unintentional locations like waterways.
Rainfastness additives are ingredients that can, through a variety of different modes of action( MoAs), maintain the efficacy of a plant protection product despite rainfall events. They usually increase the adhesion and / or spreading of the formulation on the leaf and the choice of additive is heavily informed by the properties of the actives. Actives that work by a contact MoA and need to sit on the leaf surface, which is common for insecticides, have very different requirements compared to a systemic herbicide that needs to penetrate the leaf cuticle.
The main types of rainfastness additives are:
• Super-spreaders
• Uptake enhancers
• Stickers
Super-spreaders
Trisiloxane adjuvants can increase rainfastness by providing‘ super-
Figure 1- Croda’ s rainfastness screening method
spreader’ properties to the formulation; they are highly effective wetting agents that very quickly form an even layer across the leaf and greatly accelerate the drying process.
This works well for some additives but can be counterproductive for many others; for example, if a super spreader is applied with an active ingredient that needs to be hydrated to be efficacious, it can result in the formulation not being hydrated long enough to be effective due to the faster drying time.
Additionally, hydrophilic actives( especially those that need to sit on the leaf surface) may have inherently low rainfastness performance due to their ease of redissolution, exacerbated by these high performance wetters resulting in even more of the active washing away at the next rain event.
20 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981