ISAA Conference Presentations and Posters – Highlights

A number of papers and posters were devoted to the use of surfactants and other adjuvants to enhance biological activity of pesticides by various modes of action such as:

* Reducing the dynamic surface tension of spray droplets
* Reducing the contact angle between spray droplets and leaf surfaces
* Increasing the retention and spreading of droplets on leaf surfaces
* Increasing translocation and uptake of pesticides into plant leaves

Many surfactants are available to achieve these effects either alone or in admixture with mineral or vegetable oils. Nonionic surfactants (NIS) are often used as adjuvants by adding them to pesticide formulations, or by adding them to spray tank mixtures. Nonionic surfactants of the ethyleneoxide condensate type (ethoxylates) are popular because they are available in a wide HLB range from non-polar to very polar with increasing solubility in water. Researchers develop the optimum bioenhanced pesticide formulation by testing for product physical properties and biological efficacy.

In the USA many surfactant and oil based mixtures are made for tank mixing with pesticide formulations. This approach gives farmers a greater degree of freedom to select the optimum mixture for their application. In the USA tank mix adjuvants do not require EPA approval in the same way as pesticide formulations. However, it is necessary to test the adjuvants with pesticide products in order to get a label approval for use application.

The situation in Europe is that adjuvants are usually built in to formulations so that farmers get an optimised product in a single pack. Registration of the whole formulation, including the adjuvant, is necessary in European countries.

Superspreaders

Spreading of trisiloxane surfactant solutions on hydrophobic surfaces such as plant leaves has been discussed in scientific literature for more than 20 years and can significantly improve the spreading of pesticide formulations. A popular superspreader used as a tank mix additive is Silwet L-77 supplied by a number of adjuvant companies. This can result in leaf coverage that is 10-30 times greater than with conventional surfactants. Evonik have developed a new product based on a mixture of a trisiloxane superspreader with an acrylate emulsion sticker.
 
Surfactants and solvents with low toxicity and environmental impact

Under increasing pressure from registration authorities many companies are now looking for surfactants and solvents with low environmental impact and low toxicity to mammals, especially for skin and eye irritation. The aim is to register products with few if any hazard and caution symbols on the product labels, and ultimately to have “Clean Labels”. This trend has meant that alcohol ethoxylate surfactants have been developed by many surfactant companies to replace nonylphenol ethoxylate surfactant (NPE’s) in pesticide formulations, especially in Europe. NPE’s are still used in the USA but are now being reviewed by the EPA.

Replacements are also being developed to replace NMP as a co-solvent in many EC formulations. Rhodia introduced a new polar co-solvent called Rhodiasolv PolarClean which is suitable for a number of active ingredients. The new solvent is non-flammable, has a high boiling point of 280°C and a low freezing point of -60°C. It also has no VOC problems.

Surfactants based on natural sustainable materials

Alkylpolyglucosides (APG) have been developed by many surfactant companies as low toxicity surfactants made from sustainable materials. They exhibit low dynamic surface tension and are used as built-in adjuvants for pesticide formulations as well as for tank mixes.

A range of more hydrophobic (lipophilic) surfactants based on ethoxylated aducts of saccharose has been developed by Cognis. Esterification of these materials leads to a new class of label-free non-ionic surfactants which are very effective at enhancing the biological activity of pesticides. These new surfactants have good toxicological and ecotoxicological profiles and can be added to the formulation or to the spray tank.

Adjuvants for glyphosate to replace TAMEO

Tallowamine ethoxylate adjuvants (TAMEO) have been used for many years as the standard surfactant to enhance the biological activity of glyphosate formulations. However, TAMEO has become a problem due to its aquatic toxicity and eye irritancy. Surfactant companies have now developed a number of safer adjuvants which can replace tallowamine ethoxylate in glyphosate formulations. For example, APG’s can be mixed with alcohol ethoxylates to give satisfactory biological activity in glyphosate formulations. Monsanto, Syngenta and other companies have done considerable work in this area and have patented their preferred adjuvants and mixtures for glyphosate.

Standard formulations of glyphosate at 360 g/l of glyphosate acid are based on the isopropylamine salt of glyphosate acid. It was not possible to make high strength formulations with the isopropylamine salt, so other salts such as the ammonium salt or the potassium salt of glyphosate acid up to 540 g/l of glyphosate acid have been developed. These formulations also require suitable surfactant adjuvants.

Surfactants for OD formulations

Most dispersions of pesticide particles are suspended in water to produce suspension concentrates (SC) formulations. However, some active ingredients such as sulfonylurea herbicides are not stable in water and need to be dispersed in an oil medium. These are known as OD formulations and require special surfactant dispersing agents for a non-aqueous medium. Bayer CropScience developed suitable formulations using dioctyl suphosuccinates as dispersing agents. Other dispersing systems with oil soluble dispersing agents are possible. Evonik have developed an OD formulation of nicosulfuron using dispersing agents based on modified phosphate polyethers or aliphatic fatty acid derivatives. Evonik also has a new thickener for OD formulations called Aerosil 380.

OD formulations are claimed to have enhanced activity due to the spreading effect of the oils in the formulation.

Report written by Alan Knowles, FORM-AK Ltd, UK

About Agropages.com

Agropages.com is a global leading provider of agrochemical market service. Agropages.com focuses on up-to-date industry news, features, market reports and products selling & buying information.

For more information, please visit: www.agropages.com