How to use a pump or backpack sprayer

A pump sprayer is a tank you pressurise by hand. Backpack versions carry more and pump as you walk. Both let you control the water volume, which matters for any product whose label gives both a product rate and a water volume per area. They’re also the right tool for spot spraying individual weeds rather than treating the whole lawn.

This guide covers choosing and checking a sprayer, calibrating it with water, mixing exactly, spraying evenly and safely, and cleaning up.

Choosing a sprayer

• Hand-held pump-up sprayers (about the size of a watering can) suit small lawns, spot spraying and garden edges.
• Backpack sprayers hold more and let you pump with one hand while spraying with the other, so pressure stays steadier over a large area.
• Nozzles matter. A fan nozzle gives an even strip for broadcast spraying. An adjustable cone nozzle suits spot spraying. Some sprayers come with a pressure-regulating valve or nozzle, which keeps output steady as the tank pressure drops.

Whatever you buy, keep one sprayer only for herbicides and label it clearly. Traces of weed killer left in a sprayer can damage plants you spray later with something else.

Before you start

• Read the whole label. Rate, water volume, grass types, weeds, timing, weather conditions, protective equipment, re-entry and disposal.
• Check the label suits your lawn. It must list your grass type and the weed or pest. Buffalo is sensitive to some herbicides, so take particular care.
• Check the sprayer. Look for cracked hoses, worn seals and drips. Fill it with water and pump it up to check for leaks before you use product.
• Check the weather. You need calm conditions and no rain within any rain-free period on the label.

Calibrate with water

The label might say to apply the product in a set volume of water per 100 m². Whether you actually do that depends on your nozzle, pressure and walking speed, so you need to measure.

1. Mark out a test area of at least 10 m², for example 5 m × 2 m, on the lawn or a driveway.
2. Fill the sprayer with a measured amount of clean water and pump to your normal pressure.
3. Spray the test area at your normal walking pace, moving the nozzle steadily at a constant height.
4. Measure what’s left and work out how much you used.

Enter the figures in the Sprayer Calibration Calculator. It tells you your output per 100 m² and how it compares with the label’s water volume. If you’re putting out too much, walk a little faster or use a smaller nozzle; too little, slow down. Test again until you’re close. Write down your setting and pace so you don’t have to start from scratch next time. The how to calibrate a sprayer guide goes into more detail.

Mix exactly

Work out the product and water for your area with the Product Application Calculator, using the label rate. Then:

1. Mix outdoors, on a hard surface away from children, pets, drains and garden beds.
2. Wear the protective equipment the label lists while you handle the concentrate.
3. Follow the label’s mixing directions. Many start with partly filling the tank with water, adding the product, then topping up.
4. Measure the product with a measuring cylinder or jug kept only for chemicals. Never use kitchen utensils.
5. Mix only what you need for the area you’re treating today.

Never “add a bit extra”. A stronger mix doesn’t kill weeds faster; it risks damaging your lawn, and using a product other than as its label directs can be illegal.

Only mix two products together if both labels allow it. See the tank mixing guide.

Spraying

Broadcast spraying (the whole lawn or a large area): walk at your calibrated pace in parallel strips with a slight overlap, keeping the nozzle at a constant height. Start at the far end so you aren’t walking through wet spray.

Spot spraying (individual weeds): wet the weed’s leaves as the label directs. Don’t spray to run-off unless the label says to, and keep the nozzle low and close to the weed. See the spot-spraying guide.

In both cases, pump regularly to keep the pressure steady. Pressure changes the output, so a sprayer that has dropped pressure puts out less than it did during calibration.

Check your work. When the tank is empty, compare the area you covered with the area you planned. If you finished well short or had a lot left over, your pace or pressure changed from the calibration run. Don’t go back over the lawn to use up the extra; note what happened and adjust next time. For a weed treatment, look again after the time the label gives for the product to work, and only re-treat if the label allows it.

Weather and drift

Spray only in the conditions the label allows: not in strong or gusty wind, not when rain is forecast within the label’s rain-free period, and not on hot afternoons. Home garden herbicide labels warn against letting spray contact or drift onto plants you don’t want to kill.

A coarse spray at lower pressure reduces drift. Fine droplets stay in the air longer and travel further, so keep the nozzle close to the target. Stop if the wind picks up, and never spray towards a neighbour’s garden, a pond or a creek.

Edges, garden beds and paths

Lawn edges are where most accidental damage happens. A herbicide that is safe on your lawn can kill the shrubs and vegetables next to it.

• Spray edges with the nozzle low and angled away from the garden bed.
• Use a spray shield or hood if your sprayer has one. It stops droplets escaping sideways.
• On a breezy day, leave the edges for another time rather than risk drift.
• Keep spray off paths and driveways. Anything that lands on a hard surface can wash into stormwater drains in the next rain.

Protective equipment

Wear what the label lists. As a minimum for most lawn chemicals that means:

• chemical-resistant gloves, not cotton or leather, which soak up liquid;
• long sleeves and long trousers, with the trousers over your boots;
• eye protection, especially while mixing the concentrate;
• enclosed shoes or boots.

Some labels also require a respirator or a face shield. Wash gloves before you take them off, then wash your hands and face before eating, drinking or smoking. Wash spray clothes separately from the household washing.

Looking after your sprayer

A well-kept sprayer is more accurate and safer to use.

• Check output each season. Nozzles wear and output creeps up. Re-run your water calibration at the start of each season and after changing a nozzle.
• Replace worn seals and O-rings as soon as the tank stops holding pressure or the wand drips. Most makers sell spare-part kits.
• Clean the filter in the handle or tank outlet after each use.
• Store it clean, empty and depressurised, out of the sun, which degrades hoses and seals.

People, pets and waterways

Keep children and pets indoors while you mix and spray, and off the treated area until the label’s re-entry conditions are met. Keep spray away from fish ponds, creeks, gutters and drains. Some products are toxic to bees, so avoid spraying flowering weeds while bees are working them, as the label directs.

If someone swallows a product or gets it in their eyes, follow the label’s first aid instructions and call the Poisons Information Centre on 13 11 26.

After spraying

1. Spray any small amount of leftover mix onto the treated area at the label rate, if the label allows. Never pour leftovers down a drain or into the garden.
2. Rinse the tank, hose and nozzle with clean water, and spray the rinsate over the treated area or dispose of it as the label directs.
3. Release the pressure and store the sprayer upside down to drain, out of the sun.
4. Store the product in its original container, locked away.
5. Log the application in your Lawn Journal, including the product, rate, area and weather.

Common mistakes

• Skipping calibration and guessing whether you’ve hit the label’s water volume.
• Letting the pressure drop as you go, so less comes out by the end of the strip.
• Spraying when the label says not to, such as in heat, wind or before rain, or on stressed weeds.
• Mixing a full tank for a handful of weeds. Work out what you need and mix only that.
• Leaving mixed product in the tank for another day, unless the label allows it.
• Using the herbicide sprayer for fertiliser without thorough cleaning.

Troubleshooting