TECHNICAL | PPC109 October 2022

In this article, BASF’s competent pest consultant, Oliver Madge, gives an overview of the purpose of baiting strategies and how environmental surroundings should inform a pest controller’s choice of strategy and baits.

 “Because of the concerns the industry has over the use of rodenticides, it could be presumed that we almost fail to level the balance of risk, by using rodenticides that are not the most effective for the situation presented.”

Many attitudes towards the use and efficacy of rodenticides have changed significantly over the last few years, especially considering environmental assessments, resistance around the UK and a much greater awareness of secondary poisoning.

But how do these concerns and the Campaign for Responsible Rodenticide Use (CRRU) revised best practice impact how rodenticides are used?

The approach to the use of ‘baits’ has become more of a considered process, but which is the ‘right one’ to use and how should it be used? 

Industry concerns

In accordance with all best practices and product labels in the UK, we need to complete the various assessments, as well as read the label of course! A task-specific COSHH assessment should be second nature for everyone.

Environmental risk assessments (ERAs), which are mainly based on non-target species and any ‘potential impact’ of using rodenticides, are initially a bit harder to get your head around. The key point is that ERAs should be unique to the location (or local environment) in which the treatment is planned. 

As an industry, we provide services based on the potential of rats and mice spreading diseases, gnawing cables, causing severe economic damage and causing non-compliance with legislation or food standards. 

Because of the concerns the industry has over the use of rodenticides, it could be presumed that we almost fail to level the balance of risk, by using rodenticides that are not the most effective for the situation presented.

The safe and effective use of rodenticides is reliant on the skill and knowledge of an individual collecting all the information and forming a considered approach.

As an industry, we provide services based on the potential of rats and mice spreading diseases, gnawing cables, causing severe economic damage and causing non-compliance with legislation or food standards. 

These outcomes fall into a new term referred to as a baiting strategy, so let’s have a look at how this works in practice.

There is not necessarily a single definition – the correct baiting strategy is the best option for that situation. As with all pest management jobs, be they for rodents, insects or birds; the correct strategy is defined by the site specific conditions.

A strategy should be put together after all the information has been collected from a site survey.

To consider what a baiting strategy should look like and how it should be implemented, there are local factors that need to be included within the assessment process. 

Of course, to be in line with professional standards and the hierarchy of controls, the use of traps should also be considered as part of the eradication campaign strategy as well.

Let’s examine some examples of points to consider, but this should not be considered an exhaustive list...

Pest risk assessment

If rodent activity presents a higher risk to either human health or building structure, then it should be controlled as quickly as possible.

Multi-feeds can take much longer to effectively control a population. Single-feeds are quicker, but both have significant negative impacts if secondary poisoning occurs.

Included within this is the time to death, so when a rodent has consumed a lethal dose, it is still active for a few days, continuing to spread the risk.

Speed baiting overcomes both of these outcomes, in that it’s not bioaccumulative and stops rodents after 24 hours of a lethal dose.

Primary poisoning

This is one factor to consider, but with two potential outcomes. 

Of course, we don’t want to poison any non-targets, but when rodenticides are applied there is always a risk to some degree, we just need to mitigate this risk as much as possible and justify the options applied.

Where there is significant risk then we may need to go back to the drawing board. You should always consider what is (potentially) going to eat the bait that has been applied.

You also need to think about larger non-target species (NTS), such as a dog or a fox. Or maybe it’s a smaller animal such as a field mouse. This may sound strange, but these NTS do have different risks. 

If there are concerns that larger NTS may access the bait, then this may be mitigated by the way the rodenticides are presented. Typically, a covered and protected approach or the use of a plastic/metal tamper-resistant box (TRB) would be suitable for larger animals such as dogs.

However, external TRBs are pretty much an attraction for smaller NTS, because of the fact the boxes provide shelter and refuge and so, it may be true that this doesn’t reduce the poisoning risk but increases it.

Of course, we don’t want to poison any non-targets, but when rodenticides are applied there is always a risk to some degree, we just need to mitigate this risk as much as possible and justify the options applied.

A factor to consider in using multi-feeds to control pest activity is how much rodenticide would be required. Saturation baiting requires rodents to eat repetitively to achieve a lethal dose; bait replenishment needs to be undertaken more frequently to ensure that a surplus of bait is always available.

A lot more bait needs to be used to control the pest. This could be seen as a higher risk to the NTS.

Pulse baiting should mean a rodent consumes a lethal dose in a single feed. Some products require less consumption to achieve control, so overall less rodenticide needs to be applied.

When considering the volume to be applied, less could be applied more safely and so present less risk to NTS.

Secondary poisoning

If the risk is an animal eating the dead (scavenging) or dying (predatory) rodent, then you need to consider if the product you’re using has the most suitable active ingredient. For example, Cholecalciferol isn’t an anti-coagulant and isn’t bioaccumulative.

All traditional anticoagulants, either multi or single-feeds, build up in body tissue and have the potential to be transferred up the local wildlife food chain. So, their use shouldn’t be considered in situations where secondary poisoning is a significant risk. 

An added disadvantage with anticoagulants is that once a lethal dose has been eaten, the rodent continues to eat during the time to death which could be many days. 

So in reality these rodents could consume more rodenticide than needed and this is also retained within body tissue or stomach content.

This is so serious that if we don’t all understand what baiting strategies should look like and how they operate in practice, there may be a very simple outcome: anti-coagulants are withdrawn from the market. This a very sobering possibility and, as Dr Alan Buckle representing CRRU recently wrote, “we have all been warned”.

Cholecalciferol: Cholecalciferol stops the rodents from continually eating once a lethal dose has been consumed, which means that less bait is eaten overall. Which means that less rodenticide needs to be applied in the first place.

“Baiting strategies can change the service approach that pest controllers deliver as part of an eradication campaign.”

Resistance

CRRU is continually looking for tail samples from around the UK. These tails are used to discover whether a particular population of rats, or mice, have a resistant gene thinkwildlife.org/free-tests-of-rodenticide-resistance-status-from-crru

The Rodenticide Resistance Action Committee (RRAC) has a fantastic interactive app available on Android phones which provides updates on resistance patterns in your area.

Users who continue to apply multi-feed rodenticides and anyone who is not 100% aware of the level of resistance in their area, in both urban and rural locations, are simply adding to the overall risk associated with rodenticide use.

Resistant rodents will consume rodenticides, which are then usually replaced by the rodenticide user, as it has been eaten. 

These resistant rodents are in turn breeding, often producing resistant offspring, which will be eating the multi-feed bait. The bait is then replaced as it has been eaten and on it goes. Overall, more rodenticides are being applied.

Formulations

Where baits needed to be consumed or last over a longer period of time (for example in-between the usual four or six-weekly ‘routine’ cycle) a common approach was to apply more bait and/or in longer-lasting formulations, such as hard wax blocks. 

But maybe this hard block isn’t a staple food source for the target rodents, be that in an urban fast food establishment or a rural farm situation.

Formulations are also an important part of bait security within application techniques. 

Where ‘T-bag’ formulations are being used, these can provide higher palatability, certainly over hard wax blocks, but they have no preformatted hole to help secure the block.

Could the weather also affect the formulation? T-bag blocks are generally harder in colder environments, so they could be liable to snap more easily. Warmer summer months may release the oils and then they leak through their paper envelope.

Selontra® has a pre-formed hole to allow the block to be secured with wire or into a TRB without the risk of splitting, and the wrapper is designed to protect the bait while allowing the rodents to use their sense of smell to find the bait appealing.

Summary

Baiting strategies can change the service approach that pest controllers deliver as part of an eradication campaign. 

Speed or pulse baiting requires less rodenticide to be applied, which means less being applied during follow-ups (which saves money), and fewer follow-ups as the rodents will have been controlled (which again, saves more money).

How the bait is to be presented, ie covered and protected or in bait stations, is also part of the overall strategy, albeit this ‘application technique’ is also a subject matter in its own right. 

During each follow-up visit, reassess the site and remaining infestation and bait accordingly – don’t just do more of the same.

It would be great if there was a simple definition for baiting strategy – or would it? 

Every site is different, which should mean that every baiting strategy may need to be different.

The skill of a pest professional is in being able to balance the use of rodenticides and non-chemical methods, to gain effective control and minimise the risk that pests present, while also minimising local environmental impact.

NEED ADVICE?

If you're a BPCA member and you'd like technical advice on baiting strategies, get in touch.

technical@bpca.org.uk

Source: PPC109