Warren ripping costs vary dramatically depending on the type of equipment used and the terrain. The aim of ripping is to destroy the warren structure, not just to bury the warren entrances. Key points to note before landholders undertake a ripping program are:
- Ensure adequate ripping depth; 700- 900 mm penetration is usually necessary to destroy most of the sub- surface structure.
- Ripping is most effective in dry, friable soils that flow down into lower warren spaces.
- Rip when weather is hot to ensure all rabbits are underground and that survival of rabbits above ground is low. Rabbits are also less likely to be breeding in summer. The aim should also be to rip when rabbit numbers are at their lowest based on their breeding cycle and/or recent disease outbreak, or following a baiting program.
- Rip two metres beyond the edge of the warren to destroy burrows that have entrances on the edge of the warren and lead outwards.
- Cross-rip or use winged tines to ensure burrows running parallel to and between the tines are not left intact.
- Ensure that all warrens are ripped. Rabbits surviving in small missed warrens frequently re-open the larger ripped warrens from which they originated. The efficiency and effectiveness of ripping large areas can be greatly enhanced by using experienced spotters on motorbikes who log warren locations on a GPS before the ripping operation commences.
- Larger machinery may be more expensive on an hourly basis, but is often more cost-effective overall due to the following factors: able to pull more tines and therefore cover a larger area with each pass; able to rip to a greater depth and pull winged boots which usually avoids the need to cross-rip; and the weight of the machine itself facilitates warren destruction.
- Small machinery is most cost-effective for areas with low warren density or for follow-up ripping, where the travel time between warrens is high relative to the time spent ripping warrens.
- Smoothing/back blading the ripped warren complex as well as spreading seed will make it more difficult for rabbits to dig back in and will facilitate surface cover which may be essential to avoid soil erosion on sloped ground. However, these measures are only likely to be cost-effective for smaller operations in higher rainfall areas.
- Get it right the first time. There is no substitute for thoroughness. The unit costs of returning to fix a problem (by re-ripping or any other method) far exceed the additional costs of extra care in the primary treatment.
- Where possible, removing surface rabbit harbour such as scrub, briars, logs and rockpiles should also be conducted to assist long-term rabbit control provided such activities are not detrimental to farm production, biodiversity or cultural resources.
Other conventional control techniques:
Poison baiting 1080
Poison baiting is used as a primary treatment for rabbit control in agricultural lands to knock down rabbit populations. It is a particularly useful tool for reducing rabbit numbers prior to warren destruction. Key points to note before landholders undertake a baiting program are discussed below:
Notes: Carrots may also be used as a bait material but requires more preparation and deteriorates more rapidly than oat bait.
Western Australia uses a ‘one-shot oat’ technique where a small proportion (‘one in a hundred’ grains) of the oat bait contains sufficient 1080 to kill a rabbit. Free feeding is not required but the bait needs to be made available for an extended period (weather conditions need to be dry for 5-10 days).
Bait is provided in a narrow trail at 6 kg/km (2–3 trails ?20 m apart), laid in a furrow or on the soil surface, or less frequently, in a broad (5m wide) scatter trail at 10 -12 kg/km. A similar ‘one-shot’ procedure is used for the Pindone pre-mix product for controlling rabbits in WA.
Poisoned oats (2.8 g/kg pindone acid) are mixed with plain oats to a final concentraion in the mixed bait of 0.025% (ie. one poisoned oat to 11 plain oats). The bait mix is laid in a trail at ?17 kg/km. 1080 bait mix products can now be purchased from licensed retailers in most States as ready-to-lay products, provided the necessary safe-guards are met.
Pindone:
Pindone is relatively expensive (compared to 1080) but is used near settled areas where 1080 use would be inappropriate. Care needs to be taken so that native and domestic animals are not accidentally poisoned during pindone control programs.
However, an antidote does exist (Vitamin K) in case of such poisoning. Pindone can be purchased as pre- prepared oat bait which allows it to be stored and used for small operations as required.
Bait stations:
Bait stations may be used for either 1080 or pindone bait to further reduce potential non-target risks; however they are generally not as effective as trail baiting. Properly secured bait stations allow rabbit control to be undertaken without the need to de-stock paddocks.
Fumigation:
Warrens can be fumigated either by inserting aluminium phosphide tablets deep into the warren entrances or by pumping chloropicrin in with a small petrol-driven power fumigator. Key points to note before landholders undertake fumigation are:
- Rabbit warrens are not destroyed by fumigation and may readily be re- opened by other rabbits in the future, so it is only recommended in circumstances where poisoning and ripping are not possible, or to mop up the residual rabbits and prevent rapid re-establishment of the population after successful ripping programs.
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