How to make the most of your herbicides using wetters and spray additives


If you rely on herbicides to control weeds, there are a number of steps you can take to really get the most out of your chosen products. Amplifying the efficacy of your herbicide will not only help to keep costs down but can also guarantee higher yields and consequently, greater profits – an undeniable win-win. 

Wetters and spray additives are vital products that have quickly risen to popularity and developed a reputation for their effectiveness at eradicating even the most persistent weeds found in broadacre farming settings, horticultural crops, and pasture environments. They’re a must-use for anyone looking to accelerate the performance of their herbicides and tackle hard-to-kill plants in a simple and effective manner.

Looking to make the most of your herbicides? Our team of experts at Specialist Sales have decades of experience advising farmers and amateur growers alike. Keep reading as we break down everything you need to know about using spray additives and wetters to boost the performance of your chosen herbicides. 

Understanding adjuvants, surfactants, and penetrants

To best address the unique needs of your situation, it’s critical to first understand the chemistry behind accelerators like spray additives and wetters. Let’s break down three of the most common terms you’ll hear when looking to improve your herbicide performance – adjuvants, surfactants, and penetrants.

What is an adjuvant?

‘Adjuvant’ is a broad term used to describe substances that can be added to herbicide formulations to enhance efficacy. Surfactants (wetters) and spray additives are types of adjuvants. There are many subsets and formulas of adjuvants, no two of which work in an identical way – as you explore potential options, you’ll find that adjuvants all serve different functions depending on the specific requirements of your chosen herbicide and its application process.

Spray additives (AKA spray oils), for example, are a commonly used adjuvant designed to enhance the penetration of herbicides through the target weed’s waxy cuticles. Often derived from mineral or vegetable sources, spray oils soften this waxy layer, thus boosting the herbicide’s rate of entry into the plant tissues.

What is a surfactant?

Surfactants are a type of adjuvant that work by reducing the ‘surface tension’ of herbicide solutions – that is, making it easier for herbicides to be absorbed through the surface of the target plant. In typical herbicide applications, non-ionic surfactants – also known as wetters – are the most regularly used subtype. Non-ionic surfactants also help herbicide droplets to spread evenly and adhere more effectively to the leaves and stems of the chosen weed, improving coverage and absorption on the whole. This increase in ‘wetting’ significantly enhances the performance of a herbicide as it facilitates better contact between the product and the deep tissues of the target plant.

What is a penetrant?

Organosilicone penetrants are substances added to herbicide solutions to facilitate better product penetration into target plants. As a type of surfactant, they work by reducing the plant’s surface tension, allowing your chosen herbicide to spread and enter the plant’s foliage with less resistance. These additives are particularly valuable when dealing with weed species that have waxy or hairy leaves or thick cuticles, properties that can impede herbicide absorption, as they are generally more penetrative than a typical surfactant. Penetrants are also effective at evenly distributing the herbicide’s active ingredients, which leads to better absorption across all areas, including those that may be hard to reach. This helps to prevent further weed growth and reduces the development of herbicide resistance. 

What common challenges do herbicide accelerators address? 

All herbicides are formulated to kill weeds, but without proper absorption and translocation through the target weed, they’re rendered ineffective and can hinder the weed management process significantly – which is why herbicide accelerators are so critical. Adjuvants and their subtypes, including surfactants and penetrants, address a wide variety of challenges that are commonly encountered with regular herbicide use.


Adjuvants like non-ionic surfactants (wetters) and spray oils are particularly effective at tackling hydrophobia, wherein a plant’s surface has the ability to repel liquids. Depending on the type of product you select, this works either by reducing surface tension or breaking down the waxy upper layers of the plant’s cuticle, both of which lead to better conditions for herbicide absorption.


Rainfastness refers to a herbicide’s ability to withstand rainfall shortly after application without being washed away. In Australia, where unpredictable weather is commonplace and conditions can change at any moment, rainfastness poses a huge challenge to herbicide absorption and its resultant efficacy. Consequently, selecting an adjuvant with rainfast properties can help ensure that herbicides stay effective at preventing weed growth during rainy seasons or in areas where rainfall is uncertain. Supporting a herbicide’s rainfastness can also benefit the surrounding environment – if the product is more easily absorbed and less prone to runoff and leaching, this reduces the chances of environmental contamination. 

Spray droplet retention

Adequate retention of herbicide droplets on a target plant’s surface is crucial for effective weed control. Adjuvants and their subtypes work to improve spray droplet retention by modifying the physical properties of a herbicide’s droplets for increased viscosity and a lower evaporation rate. This is critical in areas with windy conditions, as drift – where the wind carries away herbicide droplets, minimising efficacy and potentially resulting in damage of non-target plants – can be a hugely detrimental factor in weed control. 

Effective uptake of active ingredients

Finally, by optimising the uptake of herbicides through modifications to the plant and/or herbicide’s structural properties, adjuvants and their respective subsets can bolster the effectiveness of active ingredients. This generally results in a faster, more thorough, and longer-lasting weed kill, which in turn has many financial and environmental benefits. 

Selecting the right herbicide accelerator

Choosing the right formula of spray oil, wetter, or penetrant is integral to achieving high-quality and sustainable outcomes on your property. While each type of herbicide accelerator has similar properties, there are small yet significant differences that should influence the type of product you select.

Wetters (non-ionic surfactants) are particularly valuable when dealing with weeds with very dense foliage and where herbicide coverage could be uneven or inadequate. By reducing surface tension, herbicides are able to coat the plant’s surfaces more effectively and comprehensively, improving absorption across broad, dense weed coverage. Tried-and-tested non-ionic surfactants include Wetter 1000, which is suitable for spray coverage when using agricultural chemicals, and Reactor Wetter 600, which is designed to be used as a spray additive when using herbicides, fungicides, insecticides, and other weed control pesticides. 

Spray additives, on the other hand, have fantastic crop tolerance but are less effective at spreading and sticking to the plant’s surface. This makes them an optimal choice when trying to tackle rainfastness amongst smaller weed quantities with no herbicide resistance. Spray oils that have proven effective at controlling unwanted plants across a variety of settings include Hasten Spray Adjuvant, and Uptake Spraying Oil, both improving the spreading, wetting, and retention of crop protection products on plant surfaces. 

Finally, organosilicone penetrants are incredibly effective at reducing surface tension, more so than any other common type of adjuvant. They have excellent spreading capabilities and are able to increase the rainfastness of your chosen herbicide with ease. As a result, they are the most effective option when attempting to address plants that have proven to be difficult to eradicate or are exhibiting signs of herbicide resistance. Effective organosilicone penetrants include  Consume Penetrant and  PCT Reactor Penetrant, which is ideal for tackling weeds in challenging hot, dry, or excessively wet conditions. 

Ultimately, embracing the strategic use of wetters (non-ionic surfactants), spray oils, and penetrants is undoubtedly a wise decision for farmers, horticulturalists, and gardeners looking to enhance herbicide performance and unlock the full potential of their chosen products. Not only are adjuvants capable of increasing weed control, but consistent and mindful use can have positive trickle-down effects on the surrounding environment and for the cost-effectiveness of your operations. Simply put, herbicide accelerators are worth the additional cost, and in the long run, the benefits are tenfold.

Need expert advice as you navigate the process of selecting and employing a wetter or spray additive? Get in touch with our knowledgeable team at Specialist Sales today.

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