Take Advantage Of Adjuvants
March 1, 2012 Adjuvants are substances used to aid or modify the action of an agrichemical or the physical characteristics of mixtures in order to enhance performance. Adjuvants include surfactants, compatibility agents, anti-foaming agents, spray colorants such as dyes and drift control agents. Adjuvants can be added to the agrichemical product at the time it is formulated by the manufacturer or by the applicator to the spray mix just prior to treatment. Adjuvants are used for numerous different reasons. Adding adjuvants can potentially increase the efficacy of the pesticide being applied or reduce off target implications. However adjuvants can easily cause crop injury or have reduced activity if label instructions are not followed. Pesticide labels usually will state if a specific adjuvant is required and the amount of active ingredient the product should contain.
Surfactants Or Surface Agents
The word “surfactant” is a general term that includes soluble detergents in liquid, and other agents that improve emulsifying, dispersing, spreading or wetting spray mixes. Surfactants increase the spray coverage on foliages and help plants absorb the spray mix or increase the exposure of a pest to the spray mix. Surfactants include extenders, compatibility agents, buffers or pH modifiers, drift retardants, defoaming agents, thickeners, emulsifying agents, wetting agents (spreaders), crop oil concentrates, and stickers.
Emulsifying Agents
These are surfactants that promote the suspension of one liquid in another. There are two types of emulsions used in the applications of pesticides. One is “oil-in-water”, these are used to allow oil-soluble pesticides to be applied as water spray. The second type is “water-in-oil” emulsion; these are usually viscous and are used to improve resistance of spray mixes to rain, improve accuracy of delivery of the pesticide and enhance activity.
Wetting Agents
These materials are also known as spreaders. They improve the ability of a given pesticide to increase the area of contact and spread evenly over surfaces of leaves or fruits. There are four types of wetting agents: anionic, cationic, non-ionic and amphoteric. Anionic and cationic surfactants have electrical charges in water while non-ionic surfactants do not have an overall electrical charge. Amphoteric may have positive or negative charges depending on the pH of the solution. Most herbicides will recommend the use of non-ionic surfactants. It is essential to read the pesticide label to determine what type of wetting agent to use.
Crop Oil Concentrates
A crop oil concentrate refers to products that contain 80 to 85% petroleum or vegetable oil plus 15 to 20% surfactant and emulsifiers. An emulsifiable oil generally refers to products that contain about 98% oil and 1 to 2% emulsifiers. This group is often called nonphytotoxic oils and phytobland oils.
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Silicone Surfactants
Silicone surfactants are silicone-based and provide a tremendous reduction in water surface tension at very low concentrations. Typical concentrations range from 0.10 to 0.25% on a volume/volume basis.
Stickers
Stickers are adjuvants that cause the pesticide to adhere or stick to the target. They may be measured in terms of resistance to time, wind, water, mechanical action or chemical action. Stickers prevent runoff of the spray mixture from the target vegetation. By increasing the amount of spray remaining in contact with the vegetation and increasing the contact time of the herbicide, the desired result is an increase in the effectiveness of a pesticide application.
Compatibility Agents
These products allow simultaneous application of liquid fertilizer and agrichemical, or two or more agrichemical formulations, as a uniform tank mix. These products prevent the formation of clumps and are used primarily when the carrier solution is a liquid fertilizer. When several agrichemicals are combined it is always recommended to do a compatibility test in a jar to determine the stability of the mixture. If any clumping, separation, thickening, and heat release occur there is an incompatibility problem, the different agrichemicals should not be mixed together. The procedure for a compatibility test is often outlined on a pesticide label.
Acidifiers And Buffers
An acidifier is added to a mixture to lower the pH. On the other hand, buffers are compounds that when combined in solutions cause the spray mix to resist changes in pH. Buffers have a characteristic limited range of pH over which they are effective, they can change the pH of a water solution to a certain level, which will be maintained even if the pH of the solution changes. Acidifiers do not have a buffering action. Most pesticide solutions or suspensions are stable between pH 5.5 and pH 7.0 (slightly acidic to neutral). Above pH of 7.0 or higher, pesticides may be subject to degradation. Water pH in Florida is usually pH 7.0 or higher making some pesticides highly susceptible to degradation. Acidifiers and buffers must be added to the tank mix water first. The water must be neutralized or acidified prior to adding pesticides and adjuvants. Check the product label to determine if the pH of the water may impact the stability of the agrichemicals to be used.
Anti-foaming Agents And Spray Colorants
These are products used to inhibit or prevent the formation of foam when pesticide mixtures undergo mixing or agitation in the spray tank. Anti-foaming agents should be added as the tank is being filled for better results. On the other hand, spray colorants are used so that the pesticide applicator can see the areas that have been treated in the field and prevent overlap.
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Drift-Control Agents
A material used in liquid mixtures to prevent drift. Drift control agents are also known as “deposition aids” and improve on-target placement of the pesticide spray by increasing droplet size. Drift reduction can reduce efficacy of some pesticides but may be well worth using it when spraying agrichemicals in sensitive areas.
Surfactant Selection (Source: Adjuvants- EDIS Publication SS-AGR-109)
The numerous types of surfactants available often lead to confusion. The following suggestions will aid in selecting a suitable surfactant:
1. Purchase a surfactant specifically manufactured and marketed for agricultural use. This is the case particularly for non-ionic surfactants, where only those sold specifically for pesticide use should be used.
2. Purchase a surfactant on the basis of percentage active ingredient. For example, it is less profitable to purchase a product with 10% active ingredient at $4/gal than it is to purchase a product with 85% active ingredient at $12/gal.
3. Isopropyl alcohol or water should not be considered as active ingredients. If the label on the container does not specifically state the percentage active ingredient in the container, ask the dealer for this information.
4. Products manufactured for household use should not be used with herbicides.
5. Be careful with claims that a surfactant may cost more, but can be used at lower concentrations than with conventional surfactants. Evidence does not exist that there is any one particular surfactant being marketed that is so effective that rates may be reduced and still obtain normal control.
6. Ignore claims such as: the surfactant contains a silicone or some other agent that will help keep the spray equipment clean, or the surfactant increases water pentration into the soil, or the use of the surfactant will increase root penetration and nutrient uptake by the crop.
7. There are no “miracle” surfactants. There are none that perform substantially better that justify a significant price increase.
8. Some products are recommended to be used with certain surfactants. Consult the label for the approved list.
Choosing the appropriate adjuvant will allow for the maximization of efficacy, mitigation of off-target effects or both, however it is critical to make sure that the adjuvants being used are appropriate for the application being made. In some instances, the adjuvants may not work as intended.
Disclaimer. The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer’s label. Use pesticides safely. Read and follow directions on the manufacturer’s label.
Sources:
Brecke, J.B and Unruh, J.B. (2003). Spray Additives and Formulations.http://edis.ifas.ufl.edu/pdffiles/LH/LH06100.pdf
Ferrell, J.A., MacDonald, G.E. and Sellers, B. (2008). Adjuvants.http://edis.ifas.ufl.edu/pdffiles/WG/WG05000.pdf
Young, B. (2012). Compendium of Herbicide Adjuvants. 11th Edition.http://www.herbicide-adjuvants.com/index.html
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