Pest & Disease Factsheet - Rodenticides

Responsible use in ornamental horticulture.

Image: Dove Associates
Image: Dove Associates

The brown rat (Rattus norvegicus) — also known as common rat, street rat, sewer rat, Norway rat, brown Norway rat, Norwegian rat or wharf rat — is the main UK rural rat. They will infest any premises, recycling centres, farms, glasshouses, tunnels, rural dwellings and watercourses that provide food and shelter.

Warmer winters, declining numbers of natural predators such as red kites, barn owls, kestrels and foxes and the irresponsible use of rodenticides have allowed rats to survive and breed for longer. In some localities there may also be control difficulties due to resistance to early anticoagulant rodenticides such as warfarin. Another possible cause of higher numbers in rural areas is that stubble burning is no longer practised, leaving food such as spilled cereal grains in the fields for rats.

Rats travel to find food, water, shelter and a mate. This might be more than two miles a night in the countryside and when immediate food supplies are short or weather conditions are harsh. The degree of movement can be an important factor in the spread of problems associated with rats — namely health issues, contamination and wastage and damage to property, equipment and materials.

How to recognise them

The fur is coarse and usually brown or dark grey, while the underparts are lighter grey or brown. The brown rat is a rather large true murid and can weigh twice as much as a black rat and many times more than house mice. Brown rats have acute hearing, are sensitive to ultrasound and have a very highly developed sense of smell.


• Shoots and stems are bitten through, leaving a clean cut at an angle. Parallel grooves, where a rat’s incisor teeth have bitten into the food material, are usually visible.
• Look for tracks and droppings to confirm or to trace entry points. Rat droppings may be visible where damage has occurred. The pellets are cylindrical in shape with rounded ends and are about 15mm long and 5mm wide when fresh.
• Rats can feed on dead pigeons that have broken their necks when trying to get out of protected structures such as glasshouses and tunnels. Look out for a messy area with a large number of plucked feathers.
• Rat tunnels in the soil have an entrance diameter of 30-40mm.
• Damage is most common on lower stems and in dense canopies in crops, where the actual damage is caused by cutting the base of the stems and collecting together with leaf debris to build nests.
• Rats are fond of bulbs (daffodils, tulips), corms (irises) and tubers (dahlias). They may strip bark from trees and shrubs in autumn and winter, and attack early-flowering plants such as winter jasmins and evergreen clematis.
• Rats can also attack sweet corn cobs, pumpkins, squash and root vegetables such as carrot, parsnip, beetroot and potato tubers. Damage can occur while crops are growing and when being stored. Harvested fruits such as apples can be similarly damaged. Seeds can be consumed.

The problem

Rats cause damage to crops and foods. They will survive on food from bird feeders, poultry feed and food for pets. Rats are often infected with a bacterial disease that can also infect people, causing a form of jaundice known as leptospirosis or Weil’s disease. The bacterium is spread in rats’ urine and can persist in wet places. It infects people through cuts and abrasions or by ingestion.

Rats enjoy compost heaps. The light friable nature of the compost is ideal for burrowing. Compost that has come from a rat-infested bin or heap can be used in the garden but cannot be used growing fruits or vegetable crops that are going to be eaten raw and where the edible parts may be in contact with the soil or compost — radish, celery, cucumber, carrot, strawberry.


The main control option is the baiting technique, carrying one of the second-generation anticoagulant rodenticides. The main active ingredients of rodent baits used in the UK are bromadiolone and difenacoum, although brodifacoum, difethialone and flocoumafen are also available for use indoors.

Effective but also safe and responsible control is essential because residues of anticoagulant rodenticides, which are widely used for rodent control, are increasingly found in wildlife. That is why the industry has come together to devise the Campaign for Responsible Rodenticide Use (CRRU) to minimise the risk to wildlife.

CRRU seven-point code

Follow the seven-point CRRU code to ensure that you comply with responsible and effective practice:

1     A planned approach — carefully monitor the location of the infestation and identify the colony’s home range. Draw up a plan of the target area.
2    Use enough baiting points at locations all over the target area. Mark each location on the site plan. Using enough baiting points from the outset will minimise the time taken to achieve control and reduce exposure time for non-target species.
3    Record bait quantity at each location then note signs of rat activity at each point as the treatment period progresses. Accurately follow the rodenticide label instructions.
4    regularly collect and dispose of rodent bodies both during and after the treatment period. The carcasses may contain rodenticide and, if eaten by predators or scavengers, could be a source of wildlife exposure. Dead rats may be found for several days after eating bait and they may die 100m or more away from the baited site. Dispose of rodent bodies as recommended on the product label.
5    Never allow bait to be exposed to non-target species. Where possible, use materials already in the target area (concrete blocks, slates, bricks, etc) to protect bait from rain, dust and access by non-target species. Tamper-resistant bait stations are available and offer the highest level of protection of the bait from non-target animals and human contact. Use these where covers made of other materials may not be secure enough.
6    Regularly inspect every bait location, as recommended on the product label, and replenish accordingly. Keep a record of each inspection, what you found and any action. This is important because you are subsequently required to demonstrate good practice.
7    Remove all bait from locations at the end of the treatment period and make a record that you have done so on the site plan.

Further information
• The Control of Rats with Rodenticides: A Complete Guide to
Best Practice (
• Rodent Control in Agriculture:
An HGCA Guide (
• Rodenticides & Biocides Legislation (
• Code of Practice for Using Plant Protection Products (
• Rodent Control on Farms: User Guide ( — currently being finalised, available shortly).

Fully updated by Dove Associates.

Use plant protection products safely. Always read the label and product information before use.

Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.

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