Ag-Formulations: Trends in Enhanced Activity
and Reduced Environmental Impact 

ALAN KNOWLES

FORM-AK Formulation Consultancy Services, Tonbridge, Kent, TN11 0RT, UK

INTRODUCTION        

Farmers and growers in all the main agricultural areas of the world rely very substantially upon crop protection chemicals to help them meet the ever-increasing demand for food and other materials such as natural fibres. Consumers continue to seek higher quality and more variety of produce. This development has led to a need for a wide range of product formulations, additives and process technology to accommodate the variety of physical and chemical properties of the pesticide active ingredients. The high cost of discovering new molecules has also meant that more emphasis has been placed on re-formulation of existing pesticides and mixtures of pesticides to give improved biological effects and to provide safer products. Surfactants and other additives have also been developed to enhance the biological activity of the active ingredients and reduce the application dose rate.  

CONVENTIONAL FORMULATION TYPES

Formulations based on the older technologies are still available and represent the greatest volume of products applied to crops. Granular formulations (GR) are used for direct broadcasting to the field as pre-emergence herbicides or as soil insecticides. Solution concentrates (SL), are aqueous solutions of active ingredients which merely require dilution in the spray tank. Some solution concentrate formulations contain a surfactant, often a non-ionic ethylene oxide condensate, to assist wetting onto the leaf surface. Emulsifiable concentrates (EC) have been very popular for many years and represent the biggest volume of all pesticide formulations in terms of consumption. Emulsifiable concentrates are made from oily active ingredients or from low melting, waxy solid active ingredients which are soluble in non-polar hydrocarbon solvents. Surfactant emulsifiers are added to these formulations. Wettable powders (WP) are made from solid active ingredients with high melting points which are suitable for dry grinding. Although wettable powders are gradually being replaced, packaging in water-soluble sachets may extend their usefulness in some cases.

TRENDS TOWARDS SAFER FORMULATIONS

The most important issues which are now being addressed are:-

·        safety in manufacture and use

·        reduced hazard in transportation

·        convenience for the user

·        ease of pack disposal or re-use

·        reduction of the amount of pesticide applied

·        reduction of waste and effluent of all kinds

·        minimising environmental impact

This has led to the development of water based formulations, water dispersible granules and encapsulated formulations for controlled release. The most important water based formulations are suspension concentrates (SC) for insoluble particles, oil-in-water emulsions (EW) for oily droplets, and suspoemulsions (SE) for mixtures of particles and droplets.

Water dispersible granules (WG), or dry flowables, as they are sometimes known, are a relatively new type of formulation and are being developed as safer and more commercially attractive alternatives to wettable powders and suspension concentrates. They are becoming more popular because of their convenience in packaging and use, being non-dusty, free-flowing granules which should disperse quickly when added to water in the spray tank. They, therefore, represent a technological improvement over wettable powders and imitate liquids in their handling characteristics, with the minimum of pack disposal problems. In the USA it was estimated that WG formulations represented nearly 20% of all formulation types approved for use in 1998, compared with about 10% in Europe and a very low number in the rest of the world.

The application of controlled release technology has been slow to reach commercialisation despite interesting research and development work by the major agrochemical companies over the last 10-20 years. Controlled release formulations have the advantages of longer residual biological activity and may reduce mammalian toxicity and phytotoxicity. Microcapsules (CS) are the most important type of controlled release pesticide formulation and are produced by an interfacial polymerisation microencapsulation process.

Most pesticide formulations are applied by spraying onto crops or weeds, but this can be a wasteful process. However, a significant amount of fungicide and insecticide products are applied directly onto seeds prior to planting into the soil. Water-based flowable suspensions (FS) are more environmentally friendly than powders or solutions, have good retention on seed and are now the preferred formulation for seed treatment.

There is increasing pressure from government regulatory authorities to reduce the application load of active ingredients on the environment, and this can sometimes be achieved by including surfactants and other adjuvants in the formulation to enhance biological activity, or to use spray tank adjuvants with the spray mixture. Nonionic surfactants are often used as built-in-wetters to enhance biological activity. They can increase the solubility of the pesticide in the droplet by micellisation, making it easier for the active ingredient to enter the target. Oil-based or silicone-based adjuvants are popular as tank mix additives, especially for glyphosate formulations.

In the last few years there has been a trend towards introducing surfactants and adjuvants which are themselves more environmentally friendly in terms of biodegradability and ecotoxicity, such as replacements for nonylphenol ethoxylate nonionic surfactants. Another example, is the use of surfactants based on sugar ethers, such as alkyl polysaccharides, which have good biodegradability and low ecotoxicity especially to fish, and are being used increasingly as biological enhancing adjuvants.