What are agricultural adjuvants?
Adjuvants are products added to a spray mixture to improve how an application behaves or performs.
Depending on the product, they can help improve spreading, retention, penetration, droplet behaviour, water quality or the way an active ingredient reaches its target.
They do not control weeds, pests or diseases themselves. Instead, they support the performance of crop protection products by helping the spray work more effectively under particular crop, target and application conditions.
Choosing the right adjuvant depends on the chemistry being applied, the crop, target, water quality and spraying conditions. Used correctly, they can help improve application consistency and make better use of the products already being applied.
What are adjuvants in agriculture?
Adjuvant definition and meaning in farming
The term adjuvant covers a range of products designed to modify the physical or biological behaviour of a spray application.
Some are added to the spray tank by the operator, while others may already be included within a formulated crop protection product.
Their role varies. An adjuvant may be used to improve wetting and spreading, help a spray remain on the target surface, increase penetration, modify droplet size, condition spray water or improve mixing within the tank.
This means adjuvants should not be treated as a standard addition to every spray. The value comes from selecting a product with the right function for the application.
What is an adjuvant in herbicides and pesticides?
The role of an adjuvant depends on the crop protection product and the target.
With herbicides, an adjuvant may be used to improve retention on the leaf, spreading, penetration or, in some situations, the behaviour of residual chemistry on the soil surface.
With fungicides and insecticides, the priority may be coverage, deposition or retention, particularly where good contact with the target surface is important.
Not every pesticide application requires an additional adjuvant. Some products already contain an effective adjuvant system, while others have specific label requirements or restrictions. Product labels and current technical guidance should always be checked before adding an adjuvant.
Why are adjuvants used in crop protection?
Adjuvants can help address specific weaknesses within an application.
These may include poor wetting of a waxy surface, uneven coverage, reduced retention, difficult water quality or an increased risk of spray drift.
The aim is not simply to add another product to the tank. It is to improve a particular part of the application where there is a clear agronomic benefit.
Improving coverage, penetration and retention
Leaf surfaces differ considerably between crops and weeds. Some are relatively easy to wet, while others have waxy cuticles, hairs or upright leaves that make spray retention more difficult.
Wetting and spreading adjuvants alter the behaviour of spray droplets so they cover the target surface more effectively.
Other products are designed to improve retention, helping more of the applied spray remain on the leaf rather than bouncing or running off.
Where appropriate for the chemistry, penetration adjuvants can also help active ingredients move through the plant surface.
The required effect depends on the product and target, so more spreading or penetration is not automatically better.
Supporting herbicide and fungicide performance
Adjuvants can help improve the consistency of some herbicide and fungicide applications where crop, weed or weather conditions make application more difficult.
For herbicides, this may include improving retention or uptake on difficult-to-wet weeds, or helping residual products remain better distributed within the target soil zone.
With fungicides, the value may come from improving coverage and deposition through the crop canopy or across the leaf surface.
The benefit is product-specific. An adjuvant should therefore be selected to address a defined application issue rather than used simply to increase the perceived strength of the spray.
Reducing spray drift and improving deposition
Some adjuvants are formulated to influence droplet formation and reduce the proportion of very fine droplets that are more prone to drift.
This can improve deposition on the intended target and reduce avoidable off-target movement.
Droplet size is only one part of good spray practice. Nozzle choice, pressure, forward speed, boom height and weather conditions remain important, and all pesticide applications must comply with the product label and relevant application guidance.
Types of agricultural adjuvants
Adjuvants can be grouped according to the job they are intended to do.
Wetting and spreading adjuvants
Wetting agents and surfactants reduce surface tension and help spray droplets spread across the target surface.
They can be particularly useful where the leaf or target surface is difficult to wet and where good coverage is important.
Non-ionic surfactants are widely used in agricultural applications because they can improve wetting and retention without carrying an electrical charge.
Retention and penetration adjuvants
Retention adjuvants help droplets remain on the target following application.
Penetration adjuvants are designed to help selected active ingredients move through the leaf surface where this is required.
Oil-based products and some surfactants can perform this role, but suitability depends on the crop protection product, crop and environmental conditions.
Drift-management adjuvants
Drift-reduction adjuvants alter spray characteristics to reduce the proportion of fine droplets that are more susceptible to off-target movement.
They should be used as part of an overall application strategy rather than as a substitute for correct nozzle selection or spraying conditions.
Water conditioners and tank-management products
Spray water can influence the performance of some active ingredients.
Hardness, pH and dissolved minerals may affect certain products, and water conditioners can be used where appropriate to manage these issues.
Anti-foam products and compatibility aids may also be used to improve the handling of more complex tank mixes.
Adjuvants in herbicide programmes
Adjuvants for glyphosate
Glyphosate performance can be influenced by water quality, weed growth stage, environmental conditions and application technique.
Hard water can reduce efficacy in some situations because dissolved cations can interact with glyphosate. A suitable water conditioner may therefore be useful where water quality is known to be an issue.
This should not be treated as a reason to automatically add an adjuvant to every glyphosate application. The formulation, water source, target weed and label guidance should all be considered.
Correct rate and timing remain fundamental, with applications made to actively growing weeds at the appropriate growth stage.
Adjuvants for pre-emergence and residual herbicides
The performance of residual herbicides depends heavily on soil conditions, even coverage and the position of the active ingredient within the upper soil layer.
Some adjuvants are designed to improve deposition, retention and distribution of residual chemistry on the soil surface.
They may also help reduce movement away from the target zone in certain conditions.
However, residual herbicide performance is still strongly influenced by seedbed quality, soil moisture, application timing and subsequent rainfall.
Specific uses such as difficult-to-wet weeds
Some weeds are more difficult to wet than others because of leaf angle, waxiness or surface structure.
In these situations, an appropriate wetter, retention aid or penetrant may help improve contact between the spray and the target.
The choice should be based on the herbicide formulation and the particular weed being treated, rather than assuming one adjuvant type will suit all waxy-leaved weeds.
Spray adjuvant formulations
Adjuvants are available in a range of formulations depending on their function.
These may include soluble or emulsifiable liquids, oils, surfactant blends, water conditioners and specialist drift-management products.
The formulation affects how the product behaves in the tank and at the target surface, so compatibility with the crop protection product is important.
Adjuvant vs surfactant: what is the difference?
A surfactant is one type of adjuvant.
Surfactants alter surface tension and are commonly used to improve wetting, spreading and retention.
The term adjuvant is broader and also includes products used for drift management, penetration, water conditioning, anti-foaming and other application functions.
Put simply, all agricultural surfactants are adjuvants, but not all adjuvants are surfactants.
Choosing the right adjuvant on farm
Matching the adjuvant to the crop, product and conditions
No single adjuvant suits every application.
The correct choice depends on the crop, target, chemistry, leaf or soil surface, water quality and application conditions.
Questions worth considering include:
- Is coverage or retention the main limitation?
- Does the active ingredient need help with penetration?
- Is water quality likely to affect performance?
- Is drift management a priority?
- Does the crop protection label specify or restrict the use of an adjuvant?
The objective should always be to solve a specific application problem.
Label guidance and compatibility
Product labels and manufacturer guidance should always be followed.
Some crop protection products already contain adjuvant systems. Others require or recommend the use of a named adjuvant, while some restrict what can be added.
Where a specific adjuvant is recommended with a plant protection product, compatibility and approved-use requirements should be checked before application.
Adding the wrong adjuvant can increase the risk of crop damage, poor compatibility or reduced spray performance.
How agronomy advice supports adjuvant use
The value of an adjuvant comes from choosing the right product for the right application.
An agronomist can help assess the crop, target, chemistry, water quality and spraying conditions before deciding whether an adjuvant is likely to add value.
This may include looking at spray coverage, retention, penetration, drift management or water conditioning, as well as checking compatibility and label requirements.
The aim is a more consistent and effective application, not simply a more complex tank mix.
In summary
Adjuvants can play an important role in spray application, but their value depends on matching the product to a specific need.
They may help improve coverage, retention, penetration, droplet behaviour or water quality, depending on the application.
They do not replace good agronomy, correct product choice or appropriate spraying conditions. Used well, they can help improve the consistency of crop protection applications and make better use of the chemistry already being applied.
Speak to your Agrii agronomist to discuss where an adjuvant may add value within your crop protection programme.