Formulating for the Grower

Certis Biologicals' research and development team navigates multi-faceted challenges to create effective, stable and user-friendly biological products for the grower. Their innovative approaches drive positive change in agricultural sustainability and performance.

As consumer concerns over environmental impact and food safety continue to escalate, growers have shifted toward biological pest management solutions. Biologicals use natural sources like microorganisms and plant extracts to provide protection and nutrition to crops. Because their efficacy is attributed to multiple modes of action, biologicals offer a promising complement to conventional chemical pesticides through improved resistance management. Our goal at Certis Biologicals is to create safe, effective and user-friendly crop protection products. As a Formulation Scientist, it is my responsibility to keep growers’ best interests in mind while addressing consumer concerns and navigating domestic and international regulatory policies. A case study is provided below to illustrate the multiple challenges associated with biopesticide formulation development. 

Case study: A fungal oil dispersion

One of my most recent challenges has been to create a liquid formulation for one of Certis Biologicals’ fungal active ingredients. Liquid products are typically preferred by growers for their ease of use: 

1. Liquids are packaged in resealable jugs whereas solids are oftentimes packaged in non-resealable bags. The product may lose efficacy if it is not resealed properly, and the risk of spillage is higher for a flexible bag than for a rigid jug.  

2. Liquids incorporate into mix tanks more quickly than solids.

3. Liquids typically remain dispersed/suspended in mix tanks longer than solids.

4. Liquids contain no dust.

However, liquid biopesticides, especially ones in which the active ingredient is a fungus, present specific challenges to the Formulation Scientist:

1. Hydrophobicity. Fungal spores can be cultivated via liquid or solid fermentation. Liquid fermentation produces blastospores, and solid fermentation produces conidia. Although conveniently hydrophilic, blastospores tend to be more difficult to preserve in biopesticide formulations than hydrophobic conidia. Thus, conidia are often preferred as the active ingredient for fungal products. 

   
   

   The two most prominent liquid formulation options for microbial actives are water-based suspension concentrates (SC) or oil dispersions (OD). Because conidia are hydrophobic, wetting agents and dispersing agents are required to formulate a suspension concentrate. However, storing fungal spores in water poses a shelf-life challenge. Conidia will sporulate in the presence of water, and if there are no nutrients in the formulation, they will die. If nutrients are present in the formulation, the conidia will germinate, producing hyphae that can thicken the formulation to the consistency of sludge over time.

   
   

   An oil dispersion is a more suitable formulation choice than a suspension concentrate for liquid fungal products. Oil wets hydrophobic actives, and conidia will not sporulate in oil. However, oil dispersions pose their own set of challenges, which are discussed in items 2 through 5 below.

   
   

2. Homogeneity. Both growers and Formulation Scientists prefer their liquid biopesticides to be homogenous. Separation as an aesthetic is sometimes associated with efficacy and may prompt questions such as, ″Is this product still efficacious or is it spoiled?″ or ″Once shaken, is the active ingredient evenly dispersed throughout the jug?″ 

   
   

   Lack of homogeneity can also cause ease of use issues. Although it is a good rule of thumb to always shake liquid biopesticides before use, aggressive shaking should not be required to resuspend sedimentation. An ideal liquid formulation will not separate over time, but separation is not a deal-breaker if it meets two criteria: The sediment should be easy to resuspend, and sedimentation should occur on the time scale of days, not hours, and certainly not minutes.

   
   

   With an oil dispersion, separation commonly occurs because of the difference in density between the oil and the active ingredient. To combat this separation, Formulation Scientists typically use surfactants and silicas in their formulations. However, these dispersing agents can inadvertently cause thickening issues that relate to pourability.

   
   

3. Pourability. Pourability, or the ability for a liquid to be poured from a vessel, is also associated with ease of use for the grower. If a liquid formulation is too thin or has low surface tension, it may dribble when being poured, leading to loss of product. The more common scenario is when a liquid formulation is too thick. A thick formulation will coat the sides of a jug more than a thin formulation. To recover this product, a grower may need to leave the jug tilted upside down for some time or wash out the jug with water. Although neither of these actions are necessarily deal-breakers for using the product, they are inconvenient. To prevent these inconveniences to the grower, a Formulation Scientist can add rheology modifiers to liquid formulations to reach a desirable consistency. 

   
   

4. Emulsifiability. Oil and water do not mix, which is why surfactants play a very important role in oil dispersion formulation development. A stable emulsion of oil in water correlates to an even distribution of active in the mix tank. This in turn correlates to an even distribution of active during application, which is imperative for the grower. If the emulsion is not stable, the oil will float to the surface of the mix tank. Because the hydrophobic active ingredient prefers oil i.e., has a lower chemical potential in oil, it will follow the oil and gather at the surface of the mix tank. 

   
   

   

   Homogeneity, pourability, and emulsifiability

   
   

5. Viability. I am frequently asked, ″What is the greatest challenge in biopesticide formulation?″ The answer is viability. I may make a homogenous oil dispersion that pours easily and forms a stable emulsion, but if my microbial active ingredient cannot survive at room temperature for a minimum of 6 months, I do not have a product. This shortened viability in oil dispersions can usually be attributed to the choice of oil carrier or other inert ingredients in the formulation. A stability study should always be conducted before greenlighting a product.

   
   

   A long shelf-life benefits both the manufacturer and the grower. It allows for products to be bought in advance of application and to be stored for subsequent applications. Longevity also reduces potential issues with supply chain, ensuring product availability for growers.

Poor oil dispersion vs good oil dispersion

The overarching challenge with biopesticide development is solving all formulation challenges simultaneously. For this oil dispersion case study, I was able to make a homogenous formulation with the addition of surfactants that emulsified the carrier oil. However, those surfactants thickened my formulation to the extent that it was not pourable. Once I added a rheology modifier to make the formulation pourable, it no longer formed a stable emulsion, so I then had to modify the surfactant package.

Formulation development is a cyclic process that requires research, experimentation, time and tenacity, but it is extremely rewarding when a formulation that facilitates the grower is achieved. As Stephanie Kwolek, inventor of Kevlar and winner of the Lavoisier Medal for technical achievements, once said, ″All sorts of things can happen when you’re open to new ideas and playing around with things.″

This article will be published in the AgroPages magazine 2024 Formulation&Adjuvant Technology.