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Slug control 2: handling and machine preparation

Course: Slug Control | Last Updates: 30th August 2017

Dr. David Glen
Biography >>


Slug pellets are pesticides and must be handled and stored according to label instructions. Operators must have a PA4 Certificate, either from sitting PA4 training itself or from taking PA1 and PA2 before 1994, in which case a PA4 was issued automatically.

Operators without PA4 should sit the NPTC’s new Slug Pelleting Seminar, which includes a 25 question multiple-choice test.

Good practice requires using appropriate personal protective equipment, including coveralls, gloves, Wellington boots and faceshield. Some products may be dusty, so work upwind when handling them.


Receiving pellets on to the farm carries significant risks, so ensure bags are not damaged by forklift tines, for example. They should be rejected and delivery vehicles should have clean-up kits, so ask the driver to clean up any spills.

Pellets should be stored in a dedicated chemical store, which is dry, fireproof and secure. Avoid stacking pallets on top of each other and if product is supplied in paper bags avoid storing on a concrete floor, which could allow moisture to degrade the bag.


Only ever move slug pellets by vehicle or on a trailer behind an ATV, pickup or tractor; never on the ATV itself, since that poses a risk to operators, others and the environment. For the same reason don’t leave individual bags around a field headland awaiting use.

Filling quad spreader

If loading in the yard use a dedicated pesticides filling area where spills can be cleared up more easily. The pelleter really should be treated as if it were a sprayer, and the best place to fill it is in the field, well away from ditches and watercourses, away from headlands and compacted/saturated ground. Open sacks carefully, preferably standing on a firm surface. Reseal part bags, clean up spills immediately, never leave bags unattended and check that used bags are completely empty before storing securely.

Machine checks

Check the machine over to be sure the vanes of the spinning disc are in good condition and not worn. Try to calibrate each time a new batch of pellets is used, since specifications can vary and pellet performance is variable.

First, conduct a speed check to ensure correct rpm of the spinning disc. Then make sure the mounting of the machine on the ATV is secure. Even it up using the adjusters provided. Measure height of the disc from the ground and check against what the manufacturer advises. If using an ATV, a working height of 1 metre is most commonplace for a fully laden bike, including operator. Heights vary for other machines, such as those mounted on a sprayer.

Application rate check

Check application rate for the chosen pellet and adjust machine accordingly. While a machine may operate up to 24m, this may be at the very limit of the machine/pellets being used. Working in 12m bouts at half the application rate will give more uniform spreading and potentially better slug control.

Spread pattern

Check spread pattern using proper calibration trays with baffles to catch pellets. One of the most common problems this will reveal is more pellets being thrown to one side of the machine than the other, probably because the machine is unbiased. Alter the bias, if possible.

Windy weather may also be to blame, in which case using 12m bouts rather than 24m will help. But if it is too windy to spray it is too windy to pellet.

Another problem can be fewer pellets in the end trays, suggesting the machine isn’t throwing pellets far enough, because the disc speed is too slow and/or the vanes are worn and need changing.

Ideally, machines should be tested annually. The National Sprayer Testing Scheme has been extended to include an MOT-type test for pelleters. The test protocol ensures machines are operating correctly and to the manufacturers’ specifications, and that set-up and spread pattern are correct. The cost is likely to be between £100 and £140 per machine.


  • Choose a comfortable forward speed to give a smooth ride, minimal bounce and sway: 10-15kph is normal
  • Measure 100m and time how long it takes to cover it
  • Check forward speed by dividing 360 by the time in seconds to cover 100m
  • Attach calibration shroud to machine; let machine run for 60 seconds
  • Weigh amount of pellets delivered in 60 seconds to check flow rate is correct
  • If too much, decrease the size of the opening, or vice-versa to up the rate
  • Repeat three times to get an average application rate

Static calibration can give be misleading as pellet flow can be affected by forward speed and terrain condition. To check the accuracy of the calibration apply what is calculated to be the required amount to an area of a known size, preferably away from a watercourse. If needed, adjust the applicator accordingly and repeat until accurate calibration is achieved.

If you don’t have a chute, fill the hopper with 1kg of product and record the time taken to empty while running the machine at normal speed at different feed opening settings. From this you can produce your own calibration guide.

  • Preparing to spread
  • Choose the right product
  • Take care with delivery/storage
  • Check equipment and training
  • Calibrate to avoid overdosing
  • Check spread pattern
  • Get machine NSTS tested
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