The Importance of Formulation Design

All megatrends show that output of agricultural land has to increase over the coming decades. With climate change, reduction of residue levels, increasing weed resistance, increasing disease pressure, tighter regulations (leading to less active ingredients available), shortage of water and even shortage of phosphorous in the distant future, this requirement is a major challenge for the industry. This obviously poses the question; what can the agrochemical industry do to increase output on one hand and protect the environment and improve applicator safety on the other?

 

Formulation technology is becoming increasingly important in answering this question. By designing innovative formulations agrochemical products can become more effective as well as safer. Selecting the correct formulation additives is crucial in creating successful formulations, making them as significant as the active ingredient itself. In this review I will discuss four ways that formulation design can be used to overcome these challenges.

 

Example 1: Converting emulsion concentrates (ECs) into suspensions
 

Let’s start with a simple example, EC formulations, which are easy to use with high efficacy in the field. An EC is a chemical solution and hence the formulation is physically stable. However, most ECs contain volatile aromatic solvents which are not environmentally friendly or safe for operators. A common way to replace an EC formulation is to re-formulate it into a suspension, the well-known suspension concentrate (SC). Replacing the solvent with water has two major advantages: the formulation is safer and more environmentally friendly and because water is commonly cheaper than a solvent, the cost of the formulation is reduced. So far so good. Unfortunately, a suspension generally does not perform as well in the field as an EC formulation. This is because the large suspension particles are less likely to penetrate through the leaf cuticle than when the active is delivered as a solution. Including a built-in adjuvant in the SC can overcome this issue. However, to develop a suspension concentrate with a high concentration of built-in adjuvant is a major formulation challenge. Suspensions are stabilised with dispersants and builtin adjuvants are not known to have good dispersant properties. Applying the adjuvant as a tank-mix adjuvant is the obvious solution; however local regulations which vary from region to region are sometimes a hurdle in applying a tank-mix adjuvant.

 

At Croda we use polymeric dispersants to successfully build in an adjuvant.
 

Polymeric dispersants offer superior stability by strong adsorption to the surface along with multiple anchoring points. The resultant effect is that the dispersant will not be disrupted by the incorporation of an adjuvant leading to a stable and highly efficacious formulation. Figure 1 shows a dispersant with tristyrylphenol chemistry becoming displaced by the inclusion of an adjuvant. Whereas the superior dispersancy properties of Croda’s Atlox Metasperse™ 500L means the system remains stable (Figure 2).

Figure 2: A 500g/L formulation (unstructured) formulated with Croda’s dispersant Atlox Metasperse 500L with increasing levels of a displacer molecule.

 

The inclusion of adjuvants can not only increase the efficacy of a product but it can help reduce environmental impact. An example of this is Croda’s Atplus™ UEP-100 adjuvant which is designed to increase the uptake of systemic pesticides into leaves. Figure 3 demonstrates that performance can be increased while reducing the active ingredient content by introducing an adjuvant into the system.

 

 

An effective way to protect and nurture a young seedling is by applying a seed coating containing active ingredients and nutrients. In particular the health of the young seedling affects the yield of the full grown crop. A young and vulnerable seedling cannot be protected by a foliar application. By applying a seed coating the amount of active ingredients can be reduced dramatically. Besides plant protection products the seed coating also can contain (micro) nutrients or additives like humic acid, to promote nutrient root uptake. An example of the addition of humic and fulvic acids in a seed coating formulation is Incotec’s GeniusCoat™.

 

An interesting developing trend is the application of biologicals to a seed coating. In particular natural soil occurring microorganisms like rhizobacteria and trichoderma fungi contribute to increased crop yields. The application and exploration of soil born microorganisms is relatively new and is an interesting area of R&D activity for Croda.

 

Alternatively to seed coating applications, so-called in-furrow applications have become of increasing interest. At the same time that seeds are planted, direct injection of a starter fertilizer, a plant protection product and/or biologicals are also added. By doing so the seed and young seedling are protected and nurtured in an optimum way to maximise crop yields. Compatibility of fertilizer systems and plant protection products is an issue that needs to be addressed. The high salt strength of a typical starter fertilizer system is normally devastating for the stability of an insecticide or fungicide formulation. This can be effectively managed through smart formulation development. An example of chemical and biological protection is BASF’s Xanthion®. This formulation designed for in-furrow application comprises a co-pack containing rhizobacteria and a strobilurin fungicide.

 

 

As already mentioned in the introduction, resistance is a major issue nowadays and is jeopardizing crop yields. In 1975 only a handful of weed species were reported to show herbicide resistance. In 2016 over 450 weed species are showing herbicide resistance. Besides herbicide rotation, the current strategy is applying multiple herbicides. An example is Monsanto’s Roundup® Xtend, a combination herbicide of glyphosate and dicamba, which is currently pending registrations. It is not only weeds that are developing resistance rapidly, fungi are able to develop resistance even faster. Both the popular classes of triazoles and strobilurins have lost control for a number of pathogens. Again, the strategy to combine multiple actives is common practice nowadays. Both in-can and in-tank combinations of multiple actives result in formulation complexity. With this in mind Croda developed their first star polymer, Atlox™ 4916. With its unique star structure, this molecule provides multiple chain anchoring points into both the aqueous and the oil phases. Therefore, Atlox™ 4916 has superior anchorage at the oil/water/ particle interface providing matchless stability even in the most challenging formulation conditions.

 

As well as compatibility there is also the issue of various active ingredients requiring different adjuvants to enhance efficacy. Multiple adjuvants are a secondary complexity the industry has to deal with. However, despite these formulation challenges the industry has made some progress in this area: For example the US company Winfield has developed and introduced two hybrid adjuvants systems, Destiny®HC and Superb® HC improving the efficacy of both lipophilic and hydrophilic herbicides.

 

Example 4: On target delivery
 

To get the best from our actives it is of upmost importance that they are delivered to the correct target. An undesirable effect would be for spray droplets to be delivered to a neighbouring field or even worse to nearby houses or schools. For this reason spray drift needs to be controlled. The common approach in controlling drift is by nozzle selection and correcting operating conditions. Spray drift nozzles work by creating larger droplets which mean the droplets fall more quickly and are less affected by the wind. However, larger droplets are more likely to bounce or run off the intended target and provide less coverage leading to reduced performance of the product. In conjunction to the choice of nozzle, it is now widely acknowledged that incorporating an adjuvant into a product can have a significant effect on droplet size without the negative effects of increasing droplet size. A careful balance between drift control and maximizing retention needs to be established. For this purpose Croda has built a unique designed low speed wind tunnel to study the effect of nozzles in combination with chemical drift reduction technologies such as Croda’s Atplus DRT products.

 

Conclusions
 

With the global challenges ahead it is clear that formulation teams around the globe face an enormous task. With the limited introduction of new active ingredients, innovation in the agrochemical industry must come from more effective, more complex and safer formulations.