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Knapsack sprayer weed killer

Updated: 21.10.2026

The drive has a line of weeds in the cracks, the 5 litre bottle is already empty, and the backpack you are considering prints 100 PSI on the box. A knapsack sprayer weed killer job on a home drive, path or patio is a coarse spray at low pressure, at the rate on the amateur bottle, not at that maximum. The [knapsack sprayer comparison](/hub/garden-tools/knapsack-sprayer) holds the eleven amazon.co.uk listings and their stated pressures. Products Compared used those files and public UK sources, including HSE's garden pesticides pages, not a laboratory dose trial. A qualifying purchase can earn a commission at no extra cost to you.

The drive has a line of weeds in the cracks, the 5 litre bottle is already empty, and the backpack you are considering prints 100 PSI on the box.

Our top picks

SideKing SideKing 16 L battery knapsack

Best overall

SideKing SideKing 16 L battery knapsack
7.2/10about £89.99
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Faithfull Faithfull 16 L knapsack sprayer

Best value

Faithfull Faithfull 16 L knapsack sprayer
7.1/10about £37.69
View offer
Oregon Oregon 16 L backpack sprayer

Alternative

Oregon Oregon 16 L backpack sprayer
6.9/10about £50.80
View offer
On this page
  1. 1.A driveway is a backpack job
  2. 2.Low pressure, coarse drops
  3. 3.The nozzle and the label, not the box PSI
  4. 4.Amateur bottle or professional product

A driveway is a backpack job

A path with a few weeds is a handheld bottle. A drive is a backpack, because you otherwise spend the hour walking back to the tap. The Weed Guy, updated on 23 September 2026, puts a driveway on a 15 to 16 litre knapsack rather than a 5 litre shoulder sprayer. The 15 and 16 litre tanks in this set match that size.

Low pressure, coarse drops

Best Sprayers, a UK shop, recommends about 1 to 1.5 bar for weed killers, moss killers and other garden plant-protection products, because the droplets are larger and less likely to drift. The same note allows about 0.1 bar of pressure lost for each metre you lift the lance. The Weed Guy reads professional glyphosate labels as wanting a medium or coarse spray at no more than 2.5 bar, about 36 PSI. TreeMarker's forestry note sits near 1 bar for weeds and up to about 3 bar for foliage. Your bottle's label still beats those guides. Lever against battery is on battery knapsack sprayer vs manual.
SideKing SideKing 16 L battery knapsack

Testsieger

SideKing SideKing 16 L battery knapsack
7.2/10about £89.99
View offer

The nozzle and the label, not the box PSI

Use a flat fan when you want a band along a path edge or a fence line, and a coarse cone when you want drops on a weed rather than a fog. Oregon's kit names flat fan and adjustable cone among four nozzles. A jet reaches a gap. It also blasts mix off the target if you hold it close. HSE's code tells hand-held users not to work into the wind and to keep the spray on the target. Walk so the spray goes away from you, and do not walk back through the strip you have just treated.

Amateur bottle or professional product

A home gardener using an amateur weed killer as the label says does not need a certificate for that job. HSE's garden and agricultural pages draw that line. Professional products usually need PA1 and PA6, and a large tank does not change that. If the concentrate is marked for professional use and you do not hold the certificate, do not pour it in. The sprayer itself is not NSTS-tested by being sold on amazon.co.uk. The Sustainable Use Regulations 2012 leave knapsacks off the inspection interval that applies to boom sprayers. NSTS still expects a competent person to inspect knapsacks used for professional pesticide. If the ground is public, or spraying is your job and you cannot describe the risk, use someone who can. If the tank splits with chemical already in it, stop and get competent help rather than rinsing it into a drain. For an intact sprayer and your own drive, the water test, the fill and the rinse are on how to use a knapsack sprayer.

Common questions

Is 100 PSI better for weeds?
No. One hundred PSI is about 6.9 bar on The Weed Guy's reading, and it is several times the 1 to 1.5 bar shop guidance for coarse drops. SideKing and SEESII print 100 PSI as a maximum. Other batteries here print 120 or 150 PSI. Turn the control down, or pump a manual only until the cone is coarse, and keep the nozzle close to the crack you mean to treat.
Flat fan or mist?
A flat fan for a band along the path, and a coarse cone for weeds in cracks. Mist is the wrong end of an adjustable nozzle for weed killer, because it drifts. Oregon includes both a flat fan and an adjustable cone. If the only way to get liquid out is a cloud, the pressure is too high or the nozzle is wrong. Change the tip before you walk the length of the drive.
How big a tank for a drive?
Fifteen or 16 litres is the backpack size The Weed Guy and TreeMarker treat as a normal carry for this kind of work. Twelve litres means more refills and less weight, which is the SYLSTAR battery at £41.99. Twenty litres is about 20 kg of water before the tank. Capacity does not set the dose. The label does. Mix less than a full tank when the area is smaller than a full tank of mix.
Can I use a professional weed killer at home?
Not as an untrained amateur. Amateur products from a garden centre, used in a home garden as the label says, do not need a certificate. Professional products usually need the recognised certificates, commonly PA1 and PA6 for handheld and knapsack work. The size of the sprayer does not change that. If the bottle is a professional concentrate, leave it out of this tank unless you are qualified for that product and the situation.
How do I know the rate if the label is in litres per hectare?
Read the label's own method for smaller areas if it prints one, and measure the drive rather than guessing a hectare in your head. A hectare is 10,000 square metres. A home drive is a small fraction of that, and a wrong division is how people overmix. Agrigem's point is that a single borrowed rate will not match your walk. If the label gives no home-garden method, that product is probably not the amateur bottle this page is about.

Related pages

Knapsack sprayer buying guide

Knapsack sprayer

Battery knapsack sprayer vs manual: steady or pumping

Best knapsack sprayer UK: a backpack, not a bottle

How to use a knapsack sprayer: test, fill and rinse

Sources

Public UK sources used for this comparison. Listing prices, stars and review counts are from amazon.co.uk on 19 October 2026.

  1. HSE — Garden and allotment pesticides (retrieved 19.10.2026)
  2. HSE — Agricultural pesticide FAQ (retrieved 19.10.2026)
  3. HSE — Understanding the product label (retrieved 19.10.2026)
  4. HSE — Code of practice, section 4 (retrieved 19.10.2026)
  5. HSE — Sustainable Use Regulations 2012 guidance (retrieved 19.10.2026)
  6. NSTS — Legislation (retrieved 19.10.2026)
  7. TreeMarker — Knapsack sprayer selection and calibration (retrieved 19.10.2026)
  8. The Weed Guy — How to use a knapsack sprayer (retrieved 19.10.2026)