Pest & Disease Management – Adjuvants

Adjuvants are substances that can be added to the spray tank to modify a pesticide and/or spray mixture's performance.

If there are application issues with the equipment or product, then adjuvants can help to overcome them, providing enhanced efficacy.

Although adjuvants are not classed as pesticides, they need to be registered with the Chemicals Regulation Division because they are modified chemicals.

If you know your particular needs and the limitations of the products you intend to use, adjuvants can increase the efficiency of pesticide applications. Their correct use does require some in-depth knowledge.

Adjuvants can minimise or eliminate issues such as incompatibility, instability, foaming, drift, evaporation, volatilisation, degradation, adherence, penetration, surface tension and coverage. They are designed to perform functions such as wetting, sticking, spreading, emulsifying, buffering and dispersing. They may also have some positive effect on managing water hardness. However, no single adjuvant can do all these things.

Make sure the adjuvant has been thoroughly tested and proven - test new products on a limited crop area before full-scale use. Certain pesticides need certain types of adjuvants so check the product label and only use the correct type. Do not substitute an anionic or cationic type of surfactant when a non-ionic type is recommended. For nursery crops it is usually the non-ionic types that are most suitable.

Check adjuvant labels carefully - pesticide labels need checking too, along with any information detailed in their EAMUs, to make sure an adjuvant is suitable for the site, the crop you plan to spray, the target pest, your equipment and, of course, the pesticide you plan to use. Some pesticides have additional restrictions on product choice, when using an adjuvant, to limit the risk to the environment and in some cases you are advised to reduce the pesticide rate when using an adjuvant.
Many pesticide products already contain an adjuvant, which reduces the need to add one, but not all product labels state whether they are included. If a pesticide is formulated properly for your crop, using a wetter-spreader may not give better spreading or coverage. Rather, it could increase run-off, reduce deposit and even severely damage the target plants.

Use only adjuvants manufactured and marketed for horticultural uses. Do not use industrial products or household products with pesticides because they may contain other substances that may interfere with pesticide performance and may not be approved. Adjuvants are generally categorised according to function and the main groups are as follows:

Acidifiers
These lower the pH of a pesticide spray tank solution. This is particularly important should you use a hard water for spraying. Lowering the pH of the spray solution to that nearer the leaf pH helps penetration of systemic products.
- Acidifiers include Guide, Li-700, Spraymac and X-Change.

Buffers
These tend to stabilise the pH at a constant level. Most pesticide solutions are stable between pH 5.5 and 7.0. Pesticides diluted with hard water do not always penetrate the tissue so effectively.
- Buffers include Companion Gold.

Compatibility agents
Products that facilitate more uniform mixing of liquid fertiliser and pesticides, or mixing of two or more pesticides in a tank mix with any liquid carrier.

Crop oils
Petroleumor vegetable-based product generally containing two per cent emulsifier and 98 per cent oil. These can aid product absorption by the plant because they soften the cuticle. They can also increase risk of leaf scorch in hot, sunny conditions.

De-foaming agents
Some pesticides cause foaming in the tank. This can be the result of the type of surfactant used or tank agitation. A de-foaming adjuvant can suppress both surface foam and trapped air in the spray mixture.
- De-foamers include Companion Gold and X-Change.

Drift retardants
Products used in spray mixtures to reduce drift.

Plant penetrants
Products that enhance a liquid's ability to penetrate plant roots, leaves and stems. They can be quite specific to plant types. Some herbicides and translocated fungicides can be enhanced by penetrants.
- Penetrants (for general crops) include Guide, Headland Fortune, Headland Intake, Katalyst, Li-700, Torpedo II and Wetcit.

Stickers
Adjuvants that increase the adhesion of fine solids to the leaf surface. They also decrease the amount washed off by rain or irrigation, reduce evaporation and, in some cases, reduce the ultraviolet degradation of a pesticide.
- Stickers include Addit, Asu Flex, Bio Syl, Biofilm, Biothene, Bond, Broad Flex, Companion Gold, County Mark, Designer, Desikote Max, Eco-Flex, Elan Xtra, Gateway, Gly-Flex, Gly Plus A, Grenadier, Headland Guard Pro, Impala, Intracrop Agwet GTX, Intracrop Boost, Level, Meco Flex, Nu Film P, Profit Oil, Sprayfast, Spray-Fix, Spraygard, Stika and Zigzag.

Surfactants
These modify surface tension, can influence the wetting and spreading of liquids and can modify dispersion, suspension or precipitation of a pesticide in water. For a spray droplet to perform properly it must be able to wet the foliage and spread evenly over the surface. These products alter the size of the droplet and enlarge the area of coverage, which is important for waxy and hairy leaves.

There are non-ionic surfactants (no electrical charge), anionic surfactants (negative charge) and cationic surfactants (positive charge). Non-ionic products are mostly used with systemic products in horticultural crops to help penetration. Cationic products are mainly for herbicide purposes and are not to be used generally.

- Non-ionic surfactants include Activator 90, Mixture B NF, Intracrop Questor, Intracrop Saturn, Planet, Solar, Spraymac and X-Wet. Cationic surfactants include Jogral and Ryda.

Thickeners
Adjuvants that increase the viscosity of a spray mixture, which increases the droplet size and reduces drift. These would normally be used on large-leafed tree and shrub subjects.