A wetter helps spray droplets spread across a leaf and stay there, instead of beading up and rolling off before the herbicide gets in. Use a non-ionic wetter for everyday spraying, and step up to an organosilicone wetter for waxy, hairy, dusty or stressed weeds. Always check the herbicide label first, because it tells you whether a wetter is needed at all.

  • ✓Herbicide can only work on the part of the leaf it actually touches
  • ✓Non-ionic wetters suit general spraying on easy-to-wet weeds
  • ✓Organosilicone wetters are for gorse, blackberry, rushes and other hard-to-wet targets
  • ✓The herbicide label decides whether you add a wetter, and which kind

You can buy the right herbicide, mix it at the right rate and spray on a good day, and still get a patchy result. Often the reason is simple: the spray never stuck to the weed. Choosing the right wetter for herbicide spraying in NZ is one of the cheapest ways to get more out of every tank. This guide covers what a wetter actually does, the two main types, and how to match one to the job.

What does a wetter do?

A wetter (also called a surfactant or wetting agent) lowers the surface tension of the spray, so droplets flatten out and spread across the leaf instead of sitting up as round beads. More of the leaf gets covered, and the herbicide has a better chance of getting in.

Plenty of weeds are built to shed water. A waxy coating, a layer of fine hairs, or a film of dust all stop droplets landing flat. Without help, a lot of the spray either rolls off onto the ground or dries on the surface as a bead that only touches a tiny patch of leaf.

Wetters are a type of adjuvant, which just means something you add to the spray tank to help the main product work. Other adjuvants do different jobs, such as anti-foams, markers and water conditioners. This guide sticks to wetters.

There are two main kinds you'll come across:

  • Non-ionic wetters. "Non-ionic" means the wetter carries no electrical charge, so it mixes with a wide range of products without reacting. These are the everyday, general purpose option.
  • Organosilicone wetters. Silicone-based wetters that drop the surface tension much further, so droplets spread right out, even over waxy or hairy leaves. They're built for the hard-to-wet stuff.

Why wetters matter in New Zealand

A lot of New Zealand's worst weeds are exactly the kind that shed spray, and our weather doesn't always give a long dry window after spraying. Getting the spray onto the leaf, and into it quickly, makes a real difference here.

  • Our problem weeds are tough to wet. Gorse, blackberry, broom and rushes all have waxy or spiny surfaces that droplets bounce off. They're common right across NZ hill country, roadsides and lifestyle blocks.
  • Dusty and stressed weeds are common by late spring. On the drier east coast, in places like Hawke's Bay and Canterbury, weeds along tracks, races and roadsides pick up a coat of dust, and plants under dry stress harden up. Both make spraying less effective.
  • Changeable weather shortens the rain-free window. A shower can blow through a few hours after you've sprayed. A wetter that helps the herbicide get into the leaf faster can reduce the risk of it being washed off before it's done its job.

How to choose the right wetter

Start with the herbicide label, then look at the weed in front of you. The label tells you whether a wetter is recommended, and the weed tells you which type is likely to suit.

  1. Read the herbicide label first. Some herbicides already contain a built-in wetter, some recommend adding one, and a few specify a particular type. If the label says a wetter isn't needed or names a type, follow that.
  2. Look closely at the leaf. Is it smooth and soft, or waxy, hairy, spiny or dusty? Drop a little water on a leaf. If it beads up and rolls off, that weed is hard to wet.
  3. Match the wetter to the target. For softer, easy-to-wet weeds, a non-ionic wetter is usually all you need. For waxy, hairy, woody or dusty targets, an organosilicone wetter can give better coverage and faster uptake.
  4. Mix it in the right order and at the label rate. Fill the tank partway with water, add the herbicide, then add the wetter and top up. Use the rate on the wetter label, and don't add extra "for luck".

Here's how the two types compare side by side:

Non-ionic wetter Organosilicone wetter
Best for: everyday spraying of most broadleaf weeds on softer, easy-to-wet leaves. Best for: waxy, hairy or woody targets like gorse, blackberry and rushes, plus dusty or stressed weeds.
How it spreads: flattens droplets so they cover more of the leaf. How it spreads: spreads droplets much further, often into the leaf's tiny pores, for faster uptake.
Rain risk: helps uptake, so can shorten the time the spray needs to stay dry. Rain risk: faster uptake can shorten that window further in most conditions.
Cost: lower cost per tank, a sensible default. Cost: higher cost per tank, worth it on the hard stuff.

From the Rainbow & Brown range

SprayWetter is our non-ionic wetter for general spray jobs. SuperWetter is our organosilicone wetter for the hard-to-wet targets. Both also have turf uses, such as treating dry patches on lawns and sports grounds.

Always follow product label and local regulations.

Practical tips for using a wetter

A wetter helps the herbicide do its job, but it can't fix poor timing or a bad mix. These habits get the most out of it.

  • Tip: Spray weeds while they're young and actively growing. Soft new growth takes up herbicide far more readily than old, hardened or stressed plants, with or without a wetter.
  • Tip: Avoid spraying in the heat of the day. Droplets dry fast in hot, sunny conditions, which cuts the time the herbicide has to get into the leaf.
  • Tip: Keep an anti-foam handy. Wetters can make a tank foam up, especially when filling fast. A dash of anti-foam like FoamCrusher keeps the foam down so you can see the fill level properly.
  • Tip: Use clean water. Muddy or dirty water can tie up some herbicides before they reach the weed. A wetter won't undo that.
  • Tip: Write down what you used. Note the herbicide, wetter, rate and conditions for each job. When something works well, you'll know exactly how to repeat it.

Common wetter mistakes

Most wetter problems come down to using the wrong one, or using one when it isn't needed.

Mistake: Skipping the wetter on waxy weeds. Spraying gorse, blackberry or rushes without one often means most of the spray runs off. If the label recommends a wetter, match it to the target.

Mistake: Doubling up. Some herbicides already have a wetter built in. Adding more when the label doesn't call for it costs money and can cause problems, so check the label before you add anything.

Mistake: Using kitchen detergent. Dishwashing liquid isn't made for spray tanks, foams badly and can behave unpredictably with herbicides. Use a purpose-made agricultural wetter.

Mistake: Expecting a wetter to rescue a stressed weed. A drought-hardened or frosted weed won't take up herbicide well no matter what's in the tank. Wait until it's growing actively again.

Quick wetter checklist

Run through this before you fill the tank.

  • Herbicide label checked for wetter recommendations
  • Weed identified and leaf surface checked: soft, waxy, hairy or dusty
  • Wetter type matched to the target
  • Clean water in the tank
  • Mixing order followed: water, herbicide, then wetter
  • Wetter rate taken from the label, no extra added
  • Weeds actively growing, not drought or frost stressed
  • Forecast checked for rain, wind and heat

Next step: pull out the label for the herbicide you'll use next and check what it says about adding a wetter.

Wetter FAQs

Do I need a wetter with glyphosate?

It depends on the glyphosate product. Some formulations already contain a wetter and some don't. The label will tell you whether to add one and what type. On hard-to-wet targets like gorse or blackberry, labels often recommend adding a wetter.

What's the difference between a non-ionic and an organosilicone wetter?

Both help spray droplets spread across a leaf. A non-ionic wetter is the general purpose option for everyday spraying. An organosilicone wetter spreads droplets much further and can help herbicide get into waxy, hairy or dusty leaves faster, so it's the better match for tough targets.

Does a wetter make my spray rainfast?

Not completely. A wetter can speed up how quickly the herbicide gets into the leaf, which can shorten the time the spray needs to stay dry. You still need to follow the rain-free period on the herbicide label.

Can I use dishwashing liquid as a wetter?

We don't recommend it. Household detergents aren't designed for spray tanks, they foam a lot and they can react with herbicides in ways you can't predict. A purpose-made wetter is a small cost next to a wasted tank of herbicide.

Further reading

Not sure which wetter suits your spray job? Contact us and we'll help you work it out.