Prevention and swift action best in vermin control

The key to successful vermin control is putting preventative strategies in place and being prepared to take swift action once issues emerge. This is particularly the case with rodents such as rats and mice which have excellent reproductive capabilities.

Take a female rat for example – she can produce six litters per year with a gestation period of just 21 days.

Litters commonly number between five and 10 rats and can be as high as 12 to 14 in a litter. Newborn rats can reach sexual maturity in just five to eight weeks of age with this reproductive potential capable of leading to massive issues emerging if unchecked in a relatively short period of time.

There is also an important human health consideration with rats posing a significant risk of spreading leptospirosis (Weil’s disease). Damage to equipment also needs to be accounted for with rats commonly linked to wiring being damaged.

1. Control options

Control options can be via the introduction of natural predators and manmade traps. Starting with the latter option first, the main options here are the introduction of bait boxes or rodent traps. While rodenticides are vital to prevent disease in humans and animals, protect property and equipment and ensure the highest standards of food hygiene, they must be used in a responsible manner to minimise exposure to wildlife and non-target animals.

The campaign for responsible rodenticide use (CRRU) is an excellent resource outlining best practice use and offers a reservoir of information at www.crru.ie. The CRRU promotes responsible and effective use of rodenticides through a seven point code of practice.

2. Always have a planned approach

A thorough survey of the infested site is highlighted as an essential key to success. Environmental changes which could reduce the attractiveness of the site to rodents are advised. This includes removing cover such as weeds or overgrown herbage. Where a population of rodents is present then removing cover should be delayed until after the issue has been addressed to avoid disrupting the rodents and making bait acceptance more challenging.

Access to food sources such as spilled grain should obviously be minimised and appropriate feed storage containers used.

The CRRU states that bait should only be used for as long as is necessary to achieve satisfactory control.

This should be achieved in most cases within 35 days and if not the cause should be determined.

If bait is being consumed but not effective then a more potent anticoagulant may need to be used. Where bait is not being consumed then re-visiting bait points may be necessary.

3. Always record the quantity of bait used and where it is placed

A simple plan or location list identifying areas of particular concern should be developed. This is useful to ensure all bait is removed and is also required under the Bord Bia Sustainable Assurance schemes. It is useful to note activity at different bait points.

4. Always use enough bait points

Product label instructions should be followed with regard to the size and frequency of bait points and the advice given regarding the frequency of visits to the site. Failing to use enough bait points can prolong the rodent control treatment and increase the duration of exposure risk to non-target animals.

5. Always collect and dispose of rodent bodies

The bodies of dead rodents may carry residues of rodenticides and if eaten by predators or scavengers it may be a source of wildlife exposure to rodenticides.

The CRRU states that it is essential to carry out regular searches for rodent bodies, both during and after the treatment period.

It says that bodies may be found for several days after rats have eaten the bait and that rats may die up to 100m or more away from baited site.

Rodents should be removed from the site and disposed of safely using methods recommended on the label.

5. Never leave bait exposed to non-target animals and birds

Care should be taken to ensure bait is protected sufficiently and there is no risk of accidental poisoning to other animals and birds.

The CRRU advises using natural materials where possible and highlights that the design, construction and placement of bait stations should ensure interference is minimised.

6. Never fail to inspect bait regularly

Daily inspection may be required in some circumstances. At each visit bait should be replenished as per the product label.

7. Never leave bait down at the end of a treatment

Unused bait is a potential contaminant for wildlife.

The CRRU advises that on completion of the treatment, records should be updated to signify that the infestation is controlled and that, as far as reasonably practical, all steps have been taken to ensure that the site is now free of rodenticide bait.

Cats are an obvious predator for catching mice and rats. There are numerous theories on the management of cats to enhance their hunting behaviour. A cat’s natural instinct is to hunt and a cat that is fed well but not overfed will hunt as successfully as a cat that is hungry. Some terrier dogs such as Jack Russells are also known for hunting rodents.

Owls are excellent hunters of rodents and on a normal night can catch several rodents, rising to a dozen in spring when it has chicks to feed. It is critical that if an owl is present in the area that rodenticides are not used, as owls can quickly succumb to poisoning given the large number of rodents they catch.

Owls can be attracted to your farm provided there is a place to nest and a suitable habitat to provide sufficient feed. The guidance document for the barn owl nest box action in the Agri-Climate Rural Environment Scheme gives detailed advice on all aspects of this measure.

In terms of a suitable habitat the guide states that the farm ideally should be 500m from a motorway or dual carriageway as barn owls are particularly susceptible to vehicle collisions. The altitude of the farm should also be less than 300m. A suitable habitat to provide feed should include some grass margins, low input grassland, winter bird food, overwinter stubble and unharvested cereal headlands. A suitable nesting location is a big factor in an owl selecting the site. The location should avoid negative effects of disturbance or risk of predation.

A wildlife aware training course was also established in recent years by CRRU in cooperation with the Irish Agricultural Supply Industry Standards (IASIS) with the course targeted at professional pest control technicians and other competent users of rodenticides. A list of accredited professionals is available on www.iasis.ie.