Warfarin poison may only be deployed out of doors against grey squirrels for tree protection and only between 15 March and 15 August. A successful poisoning operation will be at least as effective as cage trapping, even though few, if any, dead squirrels will be found. Squirrels may be poisoned in loft spaces all year round but in the autumn it can difficult to get them eating poison and alternative methods are best used.

Only the 0.02% warfarin bait (Grey Squirrel Bait MAPP no. 13020) may be used. The approval for Grey Squirrel Liquid Concentrate MAFF no. 06455 has been revoked.

Only trained operators can buy warfarin bait.

Poison formulations for the control of rats and mice must not be used.

The Grey Squirrels (Warfarin) Order 1973 permits the poisoning of grey squirrels with the anticoagulant warfarin for the purpose of tree protection. The Control of Pesticides Regulations 1986 specifies, on the product label (ref. MAPP 13020_Grey Squirrel Bait) how, where and when it may be deployed. These specifications include the bait, and the design and dimensions of the hopper.

Warfarin must not be used outdoors where red squirrels or pine martens occur. Operators must be trained before using warfarin. The National Proficiency Tests Council (NPTC) provides a nationally recognised Certificate of Competence for Vertebrate Pest Control, which includes grey squirrel control. The responsible use of warfarin is vital and every attempt must be made to prevent or reduce risk to other species. Hoppers should hold no more than 4 kg bait and be clearly labeled with a warning that they contain a poiso

The bait

Only the 0.02% warfarin bait (Grey Squirrel Bait MAPP no. 13020) may be used. The approval for Grey Squirrel Liquid Concentrate MAFF no. 06455 has been revoked. Users of the Grey Squirrel Liquid Concentrate who purchased product before 31 December 2006 have until 31 December 2007 to use the product (effectively August 2007 for tree protection use). Gloves (unlined or flocklined synthetic rubber or PVC to European Standard EN 374) should be worn when handling the bait and the control operation should be covered by a written Risk Assessment. Disposal of contaminated personal protective and other equipment should be through a registered waste contractor.

Hoppers

The image below shows the required dimensions of the hopper, which are set to prevent animals larger than grey squirrels gaining access to the poison. Selective access hoppers should be used. These have a flap door in the tunnel entrance preventing access by smaller animals20 and reduce bait usage by approximately 50%. There are two types of door: the weighted door which is the most reliable; and the magnetic door that is equally effective when operating correctly, but the magnet may become dislodged or lose power with age or from a coating of debris.

Hopper deployment

The choice of sites for hoppers is as described in control site selection (page 5). Sites should be spaced approximately 200 m apart and distributed throughout the control area at a density of one hopper to 1–4 ha, depending on intensity of control. At each site a hopper is placed at the base of a tree or stump with the tunnel tilted slightly down to prevent surface water flowing down the tunnel into the bait. The entrance may either face into or away from the tree/stump. Placing hoppers facing the tree 20–25 cm away limits access by non-target species, and bait spillage. The hopper is firmly secured with branch- wood or with one or two stakes which must not prevent the lid from closing fully. The hopper is held to the stake with either tying wire or bands made from a car tyre inner tube. Branchwood, stone or turf can then be used to camouflage the hopper from the public. An alternative is to dig the hopper into a bank. Occasionally, badgers, muntjac deer or feral wild boar will persistently disturb hoppers despite being well staked and secured. Another site should first be sought, but if this is not possible or it is also disturbed, the hopper must be placed above the ground either in the fork of a tree or on a platform. Hoppers sited above ground are difficult to hide.
Bark-stripping damage can occur on trees close to a well used hopper due to subordinate animals ‘waiting’ for a dominant squirrel to finish feeding. The addition of a second hopper 3–5 m away will generally curtail further damage. It is advisable to avoid placing hoppers near to final crop trees.