Croda: The Drive for Sustainable Rainfastness Technology

Katharine Gray
Lead Applications Scientist at Croda

Rainfall is one of the most important factors contributing to the growth and development of our crops worldwide. It provides water that is essential for photosynthesis and movement of nutrients throughout the plant. 78%¹ of the world cultivated area relies exclusively on rainfall for crop production, with no permanent source of irrigation. Whilst rain is a lifeline to the health of a plant, at the same time it can be detrimental when combined with pesticide applications, with as much as 90% of the initial deposit at risk of being washed away.

Rainfall can affect a pesticide application in several ways, including by:
    -    physically washing the active ingredient from the plant surface
    -    diluting the product to a less effective form
    -    extracting the active ingredient from the plant tissue
    -    redistributing the active ingredient (which can sometimes lead to phytotoxic effects)²

What is rainfastness?

Rainfastness describes the ability of an active ingredient applied to a surface to resist wash-off by rain. It can be increased through the addition of adjuvants, either built into the formulation or added to the tank. Adjuvants can both directly and indirectly improve rainfastness performance.

Direct modes of action work by sticking or increasing the adhesion of the active ingredient to the target surface increasing the retention of the deposit. These types of adjuvants are often called sticker adjuvants. There are two main mechanisms in which they can work, with some materials providing attributes that work via both modes of action:

1. Increases the adhesion or stickiness of the active ingredient to the target surface - some examples include things like synthetic latexes, terpenes, block copolymers, PVAc, waxes and celluloses.
   

2. Waterproof coating - this is often beneficial for water soluble active ingredients. When a water insoluble sticker is added it can impart hydrophobicity to the droplets creating a water-resistant barrier layer - some examples include crop and inorganic oils.
   

Indirect modes of action influence the penetration of the active ingredient so that enough of the active ingredient has been absorbed into the plant tissue prior to any rainfall events. Indirect adjuvants can be surfactants such as Croda’s Atplus™ UEP-100 that increase the rate of active ingredient uptake in foliar applications. They can also be wetting agents such as Croda’s Tween™ range that reduce the surface tension, aiding spreading onto the target surface.

The drive for new rainfastness technology

The key reason for using a rainfastness adjuvant is to increase the likelihood that a plant protection product (PPP) remains effective after rainfall (and is not washed off the intended target). This is driven by requirements for product performance, but if we look a little deeper there are many more benefits. For example, if the product is washed away, not only will the product not perform, but it could cause harm to the environment, or damage aquatic and human health. The PPP is more likely to end up in the soil or water courses, possibly damaging ecosystems. There are also economic benefits, as spraying a field again due to rainfall, costs the farmer time, fuel, and money in replacing the wasted PPP, all of which have their own sustainability impacts. It also could impact yields, as reapplications of the PPP may not be permitted in some countries if the pesticide limit has been reached.  

So why is there a drive for new rainfastness technologies? The most prominent driver is due to the proposal by the European Commission as part of its Plastics Strategy and the new circular economy plan, to ban microplastics from intentionally entering the environment. Several rainfastness technologies currently on the market contain microplastics and will fall under this regulation meaning they can no longer be used, so alternative technologies will be required. Additionally, with sustainability becoming increasingly important in the agrochemical industry globally, creating products that don’t negatively impact our environment is crucial.

New technology from Croda

Currently in development we have a new rainfastness technology, that not only will be microplastic free but have an enhanced sustainability footprint. This means we have considered the inherent properties of the technology including biodegradability, ecotoxicity, product hazards, carbon footprint and water use.

Testing for rainfastness performance

Croda has developed a new lab-based test method, paired with digital software that can be used to assess how adjuvants can reduce the pesticide deposit wash-off when washed with simulated rain droplets. This new test method allows quick screening of rainfastness performance, prior to costly and time-consuming greenhouse or field trials.

A droplet of agrochemical formulation containing the rainfastness adjuvant is applied to a hydrophobic slide. The deposit is then dried and imaged using a portable microscope. Deposit images are taken as the deposit is washed with simulated rain droplets, which can then be converted using the digital software to create semi-quantitative graphical representations of the deposit wash-off over the time course.

Initial results of the new rainfastness technology

The new rainfastness technology has been trialled in our internal lab-based test method as well as within a greenhouse trial. Two formulations have been trialled in the internal test, a 160 g/L phenmedipham SC (Figure 1) and a 250 g/L azoxystrobin SC (Figure 2). The rainfastness performance of the formulations was assessed with the rainfastness technology (3% w/w inclusion) and without. After simulated rainfall was applied, the retention of the deposit increased by 25%-45% when the Croda rainfastness technology was included.

Figure 1. Croda’s new rainfastness technology performance results using lab-based test method with 160 g/L phenmedipham SC

Figure 2. Croda’s new rainfastness technology performance results using lab-based test method with 250 g/L azoxystrobin SC

Greenhouse trials were conducted using a phenmedipham 160 g/L formulation containing Croda rainfastness technology. The performance of this formulation compared to a herbicide only control was assessed with and without simulated rainfall.

Photosynthetic efficiency, which refers to the fraction of light energy converted into chemical energy during the photosynthesis process, was used to measure performance. High values of photosynthetic efficiency, around 0.8, indicate a healthy plant whereas low values show disruption to the photosystem. Phenmedipham inhibits photosynthesis, leading to a reduction in the photosynthetic efficiency. Therefore, the lower the number, the better the retention of phenmedipham on the plants following the rain simulation.

Figure 3. The effect of adjuvants on herbicide rainfastness shown through changes in photosynthetic efficiency. Readings were taken 2 days after herbicide application. Letters on bars represent the results of a Tukey post hoc test. 5 replicates; CV% 25.1

Figure 3 confirms the results observed within Croda’s lab-based test method (Figure 1). Plants treated with Croda rainfastness technology showcase greatly improved herbicide efficacy following a rain simulation compared to the herbicide only control.

Visual differences in the performance of the herbicide with and without rain can be observed in Figure 4. After rain, the herbicide only plants show an improvement in health, compared to the plants treated with the formulation containing Croda rainfastness technology, showing the phenmedipham has likely been washed away by the rain.

Figure 4. Images of treated plants 7 days after herbicide applications, with and without rain

Closing remarks

The need for sustainable rainfastness technology is becoming increasingly clear. This need is not only driven by the impending microplastic regulation, but also by the increasing desire within the global agrochemical industry to create products that don’t negatively impact our environment. In development, Croda’s rainfastness technology has been shown to increase wash-off resistance in a range of formulations when exposed to rainfall. In addition, this technology possesses an improved sustainability profile compared to traditional technologies, and compliance to the upcoming microplastic restrictions. Croda has a goal to be sustainable – a goal we know many in our industry share. If you would like to reach out to us to discuss your sustainability requirements, we welcome the opportunity, please contact cropcare@croda.com.

¹ The state of the world’s land and water resources for food and agriculture 2021, Systems at breaking point | Produced by the Food and Agriculture Organization of the United Nations

² The effects of six adjuvants on the rainfastness of chlorpyrifos formulated as an emulsifiable concentrate, J Thacker, R Young

This article will be published in AgroPages '2023 Formulation & Adjuvant Technology ' magazine to be published this May.

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