Weed Sprayer Trailer: Tank Capacity, Axles & Safety Guide

A weed sprayer trailer can turn a long, messy spray job into a controlled, efficient run behind your ATV, ute or tractor. But if you get the tank size, axle setup or safety wrong, you can end up with a dangerous, hard-to-handle rig and patchy results.

This guide walks through how to spec a weed sprayer trailer for Australian conditions – from tank capacity and axles to brakes, pumps and safety checks – so you can spray more area in less time without putting people, machines or paddocks at risk.

What is a weed sprayer trailer?

A weed sprayer trailer is a tow-behind sprayer mounted on a small trailer chassis. It usually includes:

• A poly spray tank (often 100–400 litres for ATV and ute setups)
• A 12V or engine-driven pump
• A spray boom or boomless nozzle for broad coverage
• A hose reel and gun for spot spraying
• A single or tandem axle trailer with road-ready running gear

You’ll also see them marketed as trailer sprayers, tow behind sprayers, ATV weed sprayers or boom spray trailers in Australian retail catalogs.

If you want a real-world reference point for what a purpose-built unit looks like, GreenPRO’s Spray Trailer (GP-400T) is a good example of a trailer platform designed around stability, spraying efficiency, and property work use-cases.

How a trailer sprayer works

The pump draws herbicide mix from the tank and pushes it through either:

• A spray boom (a bar with multiple nozzles for a wide spray width), or
• A boomless nozzle (one or two nozzles that throw a wide pattern without a physical boom), or
• A hose and spray gun for spot spraying around posts, trees and sheds.

A pressure regulator and gauge control how hard you’re pushing the liquid out, and a return line sends excess flow back to the tank to keep the mix agitated.

Common use cases on Australian properties

Typical jobs for a weed sprayer trailer in Australia include:

• Paddock and pasture spraying for broadleaf weeds
• Fenceline and track maintenance
• Firebreak and roadside spraying
• Spot treating around sheds, yards and water points
• Orchard, vineyard or tree line spraying with the right boom or nozzle setup

If you’re regularly spraying more than a couple of hectares, a properly spec’d tow-behind sprayer quickly pays for itself in time and chemical saved.

 

Tank capacity – how many litres do you really need?

Tank capacity is the first big decision. Too small and you’re constantly refilling. Too big and you overload the tow vehicle or create a trailer that’s hard to control.

Match tank size to property size and terrain

As a rough starting point for Australian conditions:

• Up to 2–3 acres / 1 ha (lawn, house paddock, small block)
• A 60–100L trailer sprayer behind an ATV or ride-on mower can be enough for fence lines, driveways and lawns.
• Small acreage (5–20 acres / 2–8 ha)
• Look at 150–300L tanks. That’s a common size for tow behind sprayers used on lifestyle blocks and small farms.
• Broadacre / larger grazing blocks
• 400L+ tanks and wider booms on heavier trailers behind a ute or tractor make more sense here.

Terrain matters too. Steep, uneven country puts more stress on the trailer. In hilly areas, it can be safer to run a slightly smaller tank and make more refills rather than haul a heavy, sloshing load.

Typical tank sizes (100L, 200L, 400L+) and when they fit

You’ll often see Aussie weed sprayer trailer ranges built around:

• 100L – compact ATV rigs for fence lines, yards and smaller paddocks
• 200L – all-rounder size for small acreage and general farm work
• 400L – heavy-duty dual-axle units for larger paddocks and more serious work

Above that, you’re moving into big boom spray trailers or dedicated broadacre machines.

Weight, towing capacity and GVM explained

Water weighs roughly 1 kg per litre. So a 400L tank is 400 kg of water before you even count the trailer, pump, boom and fuel. A fully loaded 400L weed sprayer trailer can easily be 600–700 kg or more.

Three numbers matter:

• Tare weight – empty trailer weight
• Payload – how much it can legally carry
• GVM (Gross Vehicle Mass) – maximum legal loaded weight of the trailer

Your tow vehicle’s towing capacity and towball load limit must also cover the loaded trailer. If the numbers don’t stack up, you’re not just illegal – you’re unsafe. Always check the trailer’s compliance plate and the vehicle handbook, and leave a safety margin instead of running on the limit.

 

Axles, tyres & brakes – keeping the trailer stable

Once you know your tank size and loaded weight, you can spec the axle and running gear.

Single vs tandem axle trailers

For smaller rigs (say 60–200L), a single axle trailer with quality hubs, bearings and off-road tyres is usually fine.

For heavier setups (300–400L+), a tandem axle (dual axle) weed sprayer trailer has big advantages:

• Better weight distribution
• Smoother ride over rough paddocks
• More stability if you lose a tyre or hit a pothole
• Less bouncing and sway on corrugated tracks

Yes, it costs more up front, but with a big tank and boom it’s usually the safer, smarter choice.

Tyre size, suspension and ground clearance

Don’t cheap out on tyres. Look for:

• Decent diameter tyres (not tiny garden trailer wheels)
• Load-rated tyres and rims to suit your GVM
• Enough ground clearance to climb into paddocks and over washouts without bellying out the frame

Leaf spring suspension is common on weed sprayer trailer setups. For regular on-road use between properties, consider suspension and tyres rated for highway speeds, not just paddock work.

Brakes, GVM and staying legal on Australian roads

Australian road rules require brakes on trailers above certain weight thresholds, and state rules vary. As a general guide:

• Light, unbraked trailers are limited to lower GVM
• Heavier trailers need mechanical or electric brakes
• Over a higher threshold again, you may need breakaway systems

For a 400L dual-axle weed sprayer trailer that you plan to tow on public roads, electric or mechanical brakes are common and often mandatory. Check your state or territory rules and make sure the trailer is ADR-compliant and registered if required.

 

Pump, boom and hose setup for even spray coverage

Capacity and axles are only half the story. Your pump, boom and hose setup determine how evenly you lay product down.

Pump flow rate and pressure for herbicide work

Most smaller trailer sprayers use 12V diaphragm pumps. Larger units may use engine-driven pumps for higher flow and pressure. Look at:

• Flow rate (L/min) – enough to supply your boom width at the desired application rate
• Pressure (psi/bar) – enough to maintain a consistent pattern through all nozzles

Many Australian tow-behind sprayers in the 100–400L range use pumps around 7–12 L/min and 100–360 psi, depending on boom size and use case.

A pressure regulator and gauge are non-negotiable. You need to read and adjust pressure to match your target litres/ha and nozzle chart.

Boom vs boomless nozzles for paddocks and fence lines

You’ve got three main options:

• Conventional boom (e.g. 3–4 m)
• Great for uniform paddocks and lawns
• More accurate swath width
• Can be vulnerable to posts, rocks and trees
• Boomless nozzle kit
• One or two nozzles spraying a wide fan pattern (e.g. 7–15 m total coverage)
• Better for rough ground, firebreaks and fence lines
• Less hardware hanging out, but more wind-sensitive
• Combination setup
• Boom for paddocks, turn off boom and use the hose reel for spot spraying

Choose based on your main jobs. Broadacre pasture? Go wider boom or boomless. Tight laneways and tricky fencelines? Boomless plus a good hose reel can be a better fit.

Hose reels and spot spraying for awkward areas

A quality hose reel and spray gun is crucial for:

• Around sheds and yards
• Under fences
• Tight corners and obstacles

Look for:

• At least 10–30 m of chemical-resistant hose
• A comfortable gun with adjustable pattern
• A reel that doesn’t bird’s nest every second job

If you want to dial this in properly, use GreenPRO’s guide on Sprayer Hose Reel: Hose ID, Length & Pressure Ratings to match hose size and pressure so your flow stays steady at the nozzle.

And if you’re comparing reel options (manual rewind, capacity, build materials), GreenPRO’s GreenPRO Reels range is a helpful reference for common reel formats used for spraying, watering, and property work.

Safety essentials for trailer spraying

Working with herbicides behind a moving vehicle adds risk. Don’t gloss over it.

Loading, hitching and towing speed

Key rules:

• Load the trailer on level ground
• Keep heavy items low and central (don’t throw drums or tools up high)
• Make sure the coupling, chains and lighting all work before you move
• Use the correct towball size and locked latch
• Stay within the trailer and vehicle towing limits – especially on wet slopes

On paddocks and back roads, slow is safe. High speed plus a sloshing full tank is how trailers start to sway and roll.

Chemical handling, PPE and spill control

At minimum, for herbicide work you should have:

• Chemical-rated gloves
• Eye protection
• Long sleeves and long pants
• Enclosed footwear
• Clean water and a basic spill kit on or near the weed sprayer trailer

Mix herbicides following the label, and only use products registered for the target weeds and situation (grazing paddock, orchard, roadside etc). Store chemicals in a separate, ventilated area – not loose in the trailer.

Spray drift, wind, neighbours and waterways

Spray drift is one of the biggest risks with any tow behind sprayer:

• Avoid spraying in strong or gusty winds
• Drop boom height and pressure where possible to reduce drift
• Use low-drift nozzles if you’re working near sensitive crops or neighbours
• Stay well back from waterways, dams and creeks unless the label allows otherwise

Drift complaints travel faster than any weed will.

 

Pre-start and maintenance checklist

A few minutes before each spray and at the end of each season will keep your weed sprayer trailer working for years.

Checks before every spray

Before you leave the shed:

• Inspect tyres for damage and correct pressure
• Check wheel nuts and hitch components
• Confirm lights and indicators work (if using roads)
• Look for cracks in the tank, frame and drawbar
• Check hoses, fittings and the gun for leaks or wear
• Test the pump, pressure regulator and gauge with clean water
• Flush out any old mix if the trailer has been sitting

Do a short test spray and adjust pressure and speed before you start applying chemical.

Seasonal service and storage

At least once a year:

• Flush the system thoroughly with clean water (and recommended neutraliser where needed)
• Clean or replace filters and strainers
• Grease hubs and moving parts as recommended
• Touch up any chipped paint on the chassis to prevent rust
• Store with tank empty in a shaded area to protect poly from UV

If you’re in a frost-prone area, make sure there’s no water left sitting in pumps or lines over winter to avoid cracking.

 

Choosing the right weed sprayer trailer for your operation

When you’re comparing brands and models, look past the glossy photos.

Key questions to ask a supplier

Ask these before you hand over money:

• What tank sizes are available, and what’s the warranty on the tank?
• Is the axle and GVM rating suitable for my intended full weight?
• Are brakes included or available, and are they legal for my state and towing vehicle?
• What pump comes standard (flow, pressure, 12V vs engine-driven)?
• Can I choose between boom and boomless nozzles?
• How long is the hose reel, and is it chemical-resistant?
• Are spare parts (nozzles, pumps, hoses) easily available in Australia?

A good supplier should be able to calculate application rates with you and help you match boom width, pump and speed to your paddocks.

When a custom build makes sense

A custom weed sprayer trailer is worth considering if:

• You’re running organic or specialised herbicides and need specific nozzles
• You want a dual-purpose trailer (e.g. fire unit plus weed spray setup)
• You have unusual terrain and need a particular axle, tyre or suspension spec
• You spray a lot and need extra hose reels, tanks or rinse systems

Plenty of Australian manufacturers offer custom boom spray trailers and tow-behind sprayers built to suit local conditions and crops.

 

Weed Sprayer Trailer FAQs

What size weed sprayer trailer do I need?

For small blocks and house paddocks, 60–100L is often enough. Small farms and lifestyle properties usually suit 150–300L. Larger grazing paddocks often need 400L+ tanks and a heavier trailer. Always check the loaded weight against your tow vehicle’s rated towing capacity and the trailer’s GVM.

Do I need brakes on my weed sprayer trailer?

It depends on the trailer’s GVM and your state or territory rules. Light trailers may be unbraked, but heavier 300–400L dual-axle units usually require mechanical or electric brakes for legal road use. When in doubt, choose a braked trailer – it’s safer and easier to tow.

Is a boom or boomless setup better?

Booms are great for flat paddocks and lawns where you want a neat, consistent swath. Boomless nozzles are better in rough, obstacle-filled areas like firebreaks, tracks and fence lines. Many operators run both – a boom for open ground and the hose reel for awkward corners.

Can I tow a weed sprayer trailer with an ATV?

Yes, many smaller trailer sprayers are designed specifically for ATVs and UTVs. Just make sure the loaded weight is within the ATV’s towing limit and that the trailer has suitable tyres, suspension and brakes (if required). On steep or wet slopes, reduce speed and avoid sharp turns.

How fast should I drive when spraying?

Speed depends on your nozzle choice, pressure and target application rate. Many operators spray somewhere between 6–12 km/h. The key is to pick a safe, consistent speed that your tractor, ATV or ute can hold comfortably over the ground you’re in, then calibrate your rate to that speed.