Managing Rats with IPM

“You dirty rat!” This phrase embodies the frustration many feel towards rats in the garden. These uninvited guests seem ever-present, scuttling along fences, digging under the compost heap and tasting our produce.

Addressing a rat problem does not always mean resorting to toxic baits. By using a more environmentally sustainable approach, rat populations can be managed without risking the health of the environment. This article explores methods of rat control based on the principles of Integrated Pest Management (IPM).

Why Are Rats a Problem?

Before diving into control methods, it is good to understand a little more about rats and why they make such pesky pests (apart from their appetite for your ripening tomatoes).

Rats are intelligent mammals that are capable of learning and problem solving. They are also fast and flexible movers, and are omnivores that aren’t fussy about their diet. These characteristics combine to make rats great survivors wherever they are found.

Rats breed quickly. They reach puberty at around 5 weeks old and females have a gestation period of only 3 weeks. Litters often include six to 12 young, and the breeding cycle can begin again within three or four days of the female rat giving birth. You do the maths – that’s a lot of rats!

Step One: Is It a Rat?

Rats around homes in urban areas are likely to be either Black Rats (Rattus rattus) or Brown Rats (Rattus norvegicus). Australia is also home to several species of native rat and other look-alikes, so its good to make sure you know who’s taken up residence in your garden before beginning control measures.

The following characteristics should help you with an accurate ID:

Black Rat: Despite its name, the Black Rat has greyish-brown fur with a paler coloured belly and a tail longer than its body; its an excellent climber.

Brown Rat: This one does live up to its name, and has brown fur, again with a paler coloured belly. The tail is shorter than the body and Brown Rats are poor climbers, preferring to stay at ground level.

Bush Rat: A native species with charcoal to brown fur and rounded ears. The tail is shorter than the body. Bush rats are shy and unlikely to be found in inner urban areas.

Rakali (or Water Rat): A native with a large body up to 60cm long, prominent whiskers, webbed feet and a white-tipped tail. Rakali are active during the day and favour salt or freshwater swamps and shorelines.¹

Antichinus: A small native marsupial with crinkled ears that look like two lobes per ear. Compared to rats’ large front teeth, antichinus have several rows of small teeth. The tail is equal to or shorter than the body and they are good climbers.²

Using Integrated Pest Management (IPM)

IPM is a holistic approach that combines multiple strategies to manage pests. It requires an understanding of the pest’s life cycle, behaviour and habitat, but allows gardeners to use a variety of control measures without resorting to harsh chemicals. According to the Food and Agriculture Organization (FAO), IPM can significantly reduce the need for chemical pesticides, providing a sustainable alternative for both home and commercial gardens.³

Like other rodents, rats thrive in environments that provide food, shelter and water. Thus, the first step in any pest management strategy is to assess these environmental factors. Identifying the causes of infestation can help determine the most effective management practices.⁴

Physical Controls

Trapping

Setting traps can be effective, though rats quickly learn to avoid them if they see the dead corpses of other rats nearby. Old-style snap traps, when placed in areas of high activity, can capture rats without the risks associated with poison. Traps that use compressed air to deliver a fatal blow or heavy-duty bands to strangle the rats are also available, as well as designs that trap the animals live.

Set traps carefully in a covered place away from children and pets. Despite what you’ve seen in cartoons, cheese is often not an effective lure; peanut butter, pumpkin seeds or meat are more appealing. Regularly checking and disposing of corpses or of live-trapped rats in a humane way is essential.

Physical Barriers

Placing bricks on the lids of compost bins or attaching wire mesh under them can prevent rats from accessing food scraps. Similarly, keep pet food in containers with secure, closable lids.⁶

Physical barriers can also be used to protect your ripening fruit and veggies. Fruit cages made from wire mesh with a small gauge, fruit bags made from flyscreen or shadecloth covers over veggie beds are effective. Netting, even when well secured at the base, often isn’t.

Raised garden beds with steel sides can also physically block rats by making it difficult for them to climb up to crops.

Cultural Controls

Garden Clean Up

One of the simplest and most effective strategies to avoid major problems with rats is to eliminate their nesting and hiding spots. Tidying the garden and removing debris such as large piles of leaves or abandoned building materials can reduce the nooks and crannies where rats hide and nest. Storing firewood off the ground also removes another potential nesting site. Inspect your house, garage and shed for access points, especially at ground level, and fill them or block access with wire mesh.

Food Management

As mentioned above, proper food storage is essential in preventing rats from being attracted to your garden. Feed pets only what they need and store pet food securely to remove food sources. If you have chooks, ensure that their feed is kept in rodent-proof containers and that scraps aren’t left on the ground overnight.

Plant Selection

Palm trees can be a favourite hideout for black rats, while native trees provide ideal habitat for native rat predators, including possums.

Biological Controls

Encouraging natural predators can be an effective biological control method. While introducing a cat into the garden is an age-old solution, it isn’t recommended because of the proven dangers to wildlife.⁵ Contrary to what many believe, powerful owls do not feed directly on rats. Possums do, however, so welcoming possums to your garden may be helpful.

Chemical Controls

Homemade Sprays

There is a long list of herbal and other scents said to deter rats. Though there is little evidence as to their effectiveness, gardeners could try homemade sprays containing peppermint oil, spearmint oil, camphor, cloves, garlic or chilli. Ammonia is also often listed, the theory being that it is similar in smell to cat urine.

Rodenticide Baits

While setting rat baits may appear to be an easy solution to your rat problem, the animals die in pain over a long period and the baits pose risks to non-target species as well as the wider environment. Anticoagulant rodenticides, the most commonly used type, work by preventing rats’ blood from clotting. After consuming a fatal dose of the bait, rats typically die 5 to 10 days later from internal bleeding or from cuts or scratches.⁷ During this time they become weak and slow-moving and may be eaten by pets or wildlife, or become roadkill.^8,9  There is growing evidence that the chemicals in rat baits are harming wildlife including birds, mammals, reptiles and amphibians.

Rat baits come in several forms: blocks, pellets, gels, powders and pastes. Anticoagulant baits are generally divided into two types:

First Generation Anticoagulant Rodenticides (FGAR; products containing warfarin, pindone, chlorophaninone, diphacinone): Also called multi-dose anticoagulants, rats must feed more than once for the baits to be fatal. There is less chance of secondary poisoning occurring in non-target animals if they eat rats poisoned with an FGAR, but the rats themselves still die a slow and often painful death.

Second Generation Anticoagulant Rodenticides (SGAR; products containing difenacoum, brodifacoum, bromadiolone and difethialone): Rats can receive a fatal dose from one feed on SGARs, however they still die slowly. Because they often return to feed on the bait after the first feed, more toxins accumulate in their bodies and they therefore pose a greater risk of harm to non-target species. SGARs have been found not only in possums that feed on dead rats, but also further up the food chain. A 2022 survey of deceased powerful owls in Melbourne found SGARs were in 83.3% of the owls tested, even though powerful owls do not usually feed on rodents. The researchers concluded that the toxin had moved through the food chain from rats via possums to the owls.¹⁰

Non-anticoagulant rodenticides containing sodium chloride are also available and are promoted as a human and pet safe bait option. They kill rodents through dehydration. Rats must feed on the baits several times over 2-5 days, taking 3-7 days to die.

In summary, a holistic rat control program involving removing food and nesting sites, crop protection and some trapping can reduce the chances of a major rat infestation. This evidence-based approach not only protects your garden but also keeps harmful anticoagulants out of the food chain of our native animals.

 

References

1. Wildlife Victoria Fact Sheet “Native vs Non-Native”
2. Australian Museum “Is it a Rat?”
3. Food and Agriculture Organization (FAO). (2019). “Integrated Pest Management: A Sustainable Approach.”
4. Dreyer, K., et al. (2021). “Sustainable Pest Management: A Review of Integrated Approaches.” Pest Management Science\, 77(3), 1145-1154.
5. Baker, P. J., et al. (2020). “The Role of Cats in Managing Rodent Populations in Urban Areas.” Urban Ecosystems, 23(1), 11-20.
6. Morrison, R. A., et al. (2020). “Physical Barriers and Traps: Effective Strategies for Managing Rodent Pests.” Journal of Pest Science, 93(2), 287-295.
7. https://www.apvma.gov.au/resources/chemicals-news/rodenticides#what-is-an-anticoagulant-rodenticide-
8. https://www.wires.org.au/wildlife-information/wildlife-and-pesticides
9. Rattner, B. A., et al. (2020). “Risk of Secondary Poisoning in Non-target Species from Anticoagulant Rodenticides.” Environmental Toxicology and Chemistry, 39(7), 1783-1791
10. Cooke, R., et al. (2022), “Widespread exposure of powerful owls to second-generation anticoagulant rodenticides in Australia spans an urban to agricultural and forest landscape.” Science of The Total Environment, 819, 2022,
11. https://wildlifehealthaustralia.com.au/Portals/0/ResourceCentre/FactSheets/Multiple/Rodenticide_Toxicity_in_Australian_Wildlife.pdf