Formulation Development is Critical for Product Success

Developing a commercially viable formulation is a critical step in the early-stage development of a pesticide, biostimulant, fertilizer, or any type of crop production input. Formulation development should begin as soon as the active ingredient (AI) is identified, screened or scoped for potential, and a decision is made to develop it into a commercial product.

Special Considerations for Microbial Pesticides and Biostimulants

Microbial pesticides and microbial biostimulants are often grouped with conventional agricultural inputs, but their formulation presents a fundamentally different challenge. In most of these products, the active ingredient is a living organism—or a biologically active structure such as a spore that must remain sufficiently viable, stable, safe, and functional from fermentation through storage, distribution, mixing, application, and establishment in the field.

A successful microbial formulation must therefore do more than disperse an active ingredient. It must preserve the biological identity and activity of a particular microbial strain, protect it from environmental stress, deliver an effective dose to the correct biological target, and meet manufacturing and regulatory specifications throughout its shelf life. These requirements make formulation development inseparable from strain selection, fermentation, quality control, packaging, application technology, and regulatory strategy.

For conventional chemical AIs, the solvent or carrier must be chemically and physically compatible with water and all other components in the formulation.

The carrier for a microbial AI must meet the following requirements:

• Be nontoxic to the microbial strain at the intended concentration.
• Maintain suitable moisture content and water activity.
• Provide acceptable pH, ionic strength, and osmotic conditions.
• Protect the organism during drying and storage.
• Disperse or suspend adequately in the application medium.
• Produce acceptable flowability and low dust.
• Pass through pumps, screens, and nozzles.
• Adhere to the seed, foliage, root, or soil target as required.
• Be commercially available with consistent composition and microbiological quality.
• Meet regulatory and residue requirements for the intended market.

Active Ingredients Are Just the Beginning

Non-active ingredients that may be necessary or beneficial in a formulation include a whole range of diluents, solvents, surfactants, penetrants, emulsifiers, suspending agents, sequestering agents, buffering agents, stabilizers, thickeners or agents for drift reduction, volatility reduction, dispersion, antifreeze and antifoam, or even antimicrobial preservatives. The critical product testing in the field, greenhouse or laboratory must be conducted using the formulation that will eventually be sold to the farmer. If a formulation is modified during the development process, the previous testing, other than initial screening, will be rendered invalid and must be repeated with the formulation to be commercialized.

Early identification of a viable formulation is also critical for regulatory efficiency. Required regulatory studies with the formulation may have to be redone if even a small change is made in formulation ingredients. Extensive delays in registration time and increased cost of registration can occur if all ingredients in the formulation are not approved by the appropriate regulatory agencies. These regulations vary from country to country and state to state, so even the early strategic plan should include the pathways forward for expansion once commercialized.

A commercially viable formulation is one that meets criteria that includes:

• convenient application and handling,
• maximum activity,
• relative safety for workers, users and crops,
• stable in storage as well as when mixed with water or other pesticides with which it may be applied
• only approved ingredients in addition to the AI, and
• compatible with other pesticides with which it is likely to be tankmixed.

The minimum assessment to confirm commercial acceptability of a formulation should include testing for stability while packaged, stored and when mixed for application. Evaluation of stability requires evaluation for physical and chemical stability and, for microbial pesticides, biological stability.

Some formulation testing may be required by regulatory agencies, but additional testing is advised for acceptance by distributors, dealers and farmers. Of most importance to dealers, distributors and farmers are tests to confirm compatibility and storage life of the formulation.

What’s Water Got To Do With It?

For most formulations, compatibility with water is necessary. Water quality varies greatly with geographical location. Water hardness or mineral content is a major challenge for many formulations. Extremely hard or soft water can cause problems with formulations that result in a mixture that cannot be sprayed or may be sprayable but is no longer active for the desired purpose. Water quality varies considerably across the U.S. Figure 1 presents data from a United States Geologic Survey (USGS) study across the U.S. Approximately 2,100 wells were sampled, and it is easy to see the challenge this presents to pesticide manufacturers and farmers. Formulation testing should include testing for physical, chemical and biological compatibility with a minimum of three hardness levels of water to confirm compatibility. In-field testing should always document the water characteristics to determine any impact from salinity, pH or thresholds of elements.