Pest management in agriculture is perhaps the most important task that crop producers worldwide must undertake every year. To accomplish this task, crop producers must make important decisions that focus on eliminating the pest without causing harm to the crop, humans, non-targeted species, and the environment.
To control pests, therefore, it is most ideal for a pesticide to be retained on the pest long enough to penetrate the protective surface layers. Often, there are barriers that must be overcome for a pesticide to do its job. For example:
- In plants, a waxy cuticle is a protective layer that covers leaves and prevents substances from easy entry into the inner parts.
- In insects, an impervious protective exoskeleton prevents substances from gaining easy entry into the inner parts.
To enhance pesticide penetration of the outer surfaces of pests, adjuvants are used as a partner chemical in pesticidal spray application. The purpose of the adjuvant is to enhance pesticide effectiveness.
Adjuvants enhance the activity of pesticides in a variety of ways including:
- Wetting of pest
- Modifying the rate of evaporation of spray
- Improving the weatherability of spray deposits
- Enhancing penetration and translocation of pesticide
- Adjusting pH of spray solutions and deposits
- Improving uniformity of spray deposit
- Enabling the compatibility of mixtures
- Ensuring safety of the crop
- Reducing drift
Adjuvants which improve wetness, modify the rate of evaporation, improve the weatherability of spray deposits, and enhance penetration and translocation of pesticide, e.g., silicone adjuvants, are of particular importance.
Silicone Adjuvants – An Overview
Silicone adjuvants are classified as surfactants that activate pesticides by enhancing their biological activity on pests. They were developed in the 1970s and have many uses due to the unusual properties of the silicone molecule.
- Silicone is a natural element from the earth’s crust, and the second most abundant after oxygen.
- A silicone molecule consists of a silicone backbone coupled with one or more polar groups. Many types of polar groups have been described but nonionic groups are the most common types.
Some of the larger applications of silicone adjuvants for agriculture are in the manufacture of plastic foams, as spreading and wetting agents, and in personal care products.
How do silicone adjuvants enhance the performance of agricultural chemicals?
Following their discovery, silicone adjuvants gained considerable popularity and became widely used in agricultural pest management. The popularity of silicone adjuvants grew because of the following features:
- Wetting agent:
- A wetting agent lowers spray droplet surface tension which enables the spray to increase coverage of targeted pest surface by each droplet. Consequently, good coverage of pest surface leads to good pesticidal activity.
- Silicone adjuvants are able to reduce the surface tension in solutions because of the water-attracting (hydrophilic) and water-repelling (hydrophobic) groups in its structure.
- Silicone adjuvants are often referred to as superwetters because of their enhanced wetting capabilities when compared with other wetting agents.
- Silicone adjuvants are often referred to as superspreaders because of their enhanced spreading capabilities when compared with other spreaders.
- Silicone adjuvants have nonionic surfactant properties.
- Increases the surface area covered by the pesticide spray droplet.
- Causes the aqueous spray solution to adhere to target pest surface.
- Silicone adjuvants are superior stickers because they decrease the rain-free period required after pesticide spray application.
- Usually referred to as rainfastness, which simply means the amount of time needed after application before a rainfall event for the sprayed pesticide to still be effective.
- Increase the wetting and spreading of a spray solution on a pest surface that leads to increased pesticide adsorption.
- Silicone adjuvants alter the solubility relationships of the spray solution that greatly increases the absorption of pesticides.
- By lowering the surface tenson of a spray solution, silicone adjuvants can reduce the amount of foam that can develop with some pesticide products.
- Silicone adjuvants have unique properties which provide superior emulsifying capabilities compared to similar adjuvants.
- Silicone adjuvants coat tiny particles or groups of liquid molecules to prevent them from coagulating with other like molecules.
- Because silicone adjuvants are good emulsifiers, they allow oil and water solutions to mix easily.
Thus, a silicone adjuvant combines several features in one product that can make some agricultural operations, like weed control, much easier to accomplish.
Silicone adjuvants and water-soluble herbicides
Silicone adjuvants were developed for water-based herbicide applications in agriculture, horticulture, industrial, turf, vegetation management, and forestry.
The benefit of using silicone adjuvants with herbicides includes:
- The dramatic reduction in surface tension which allows maximum wetting and spreading of the spray solution on nearly all plant surfaces.
- Better wetting, spreading, and penetration of hard to wet surfaces, e.g. plants with very hairy leaves or thick cuticles.
- Enhanced activity in species, particularly grasses, that are resistant to herbicides.
- Greater ability to enhance herbicides with very low water solubility.
- Greater control of difficult-to-control weed species like yellow nutsedge (Cyperus esculentus).
- Reduced surface tension to levels low enough to allow herbicide spray solutions to enter the leaf through the stomates.
Is there a downside to using silicone adjuvants?
Care must be taken when using silicone adjuvants because they often can make the spray mixture more potent (synergize) that leads to injury to nontargeted species or crop. For example:
- Plant damage can occur if silicone adjuvants are applied with herbicides when temperatures are above 90 F.
- Because of the excellent wetting properties of silicone adjuvants, they can allow bacteria and fungi to invade plants more easily via leaf stomates.
Despite these disadvantages of using silicone adjuvants, there are plenty of benefits to using them. However, care must be taken to ensure that the benefits of their use outweigh the disadvantages.
Read the pesticide label instructions for information on the use of silicone adjuvants for agriculture with pesticide.
Tank-mix silicone adjuvant with foliar applied chemicals
Tank-mixing pesticides sometimes with other agrichemicals, like liquid fertilizers, is a routine farming procedure which can:
- Reduce the cost of application,
- Enhance the activity of certain products, and
- Widen the range of treatments in a single application.
When tank-mixing silicone adjuvants for agriculture with foliar applied chemicals, care must be taken to avoid incompatibilities, whether known or unknown. Thus, one must:
- Read the labels of the pesticide and adjuvant, and
- Follow the proper procedure when tank mixing agricultural chemicals.
- For more information, read: The ABCs of Tank Mixing Pesticides.
- How Surfactants Affect Spray Droplet Size
- Pesticide Safety: 10 Things That Must Be on a Pesticide Label
- Sun Wet Surfactant – Best Postemergence Weed Control with Herbicides
- Pesticides 101: Introduction to Pesticide Adjuvants and Surfactants
- Everything You Need to Know About Agricultural Wetting Agents
- Optimize Your Wed and Brush Control with Silnet 200
Czarnota, M. and P. Thomas. 2013. Using Surfactants, Wetting Agents, and Adjuvants in the Greenhouse. Univ. Georgia Extn. Bull. No. 1314. https://secure.caes.uga.edu/extension/publications/files/pdf/B%201319_5.PDF (Verified, Jan. 29, 2022).
Jansen, L.L. 1973. Enhancement of Herbicides by Silicone Surfactants. Weed Science 21(2): 130-135. DOI: https://doi.org/10.1017/S004317450003191X
Roggenbuck, F.C. and D. Penner. 2000. Mode of action of organosilicone adjuvants. Acta Horticulturae 527(527): 57-64. DOI:10.17660/ActaHortic.2000.527.6
Stevens P.J.G. 1993. Organosilicone surfactants as adjuvants for agrochemicals. Pesticide Science 38: 103 – 122.
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