TECHNICAL | PPC104 AUGUST 2021

The use of rodenticide baits has changed significantly over the last few years, but that’s not to say that rodenticide use has altered. How we use them, but not why we use them, has evolved.

Helen Ainsworth from BPCA member company BASF takes a back-to-basics look at rodent baiting strategies.

SPEED VIEW:

• Bait choice should be about an operator’s skill and assessment as well as label conditions
• A CoSHH assessment is needed to consider human elements, and environmental assessment to think about non-targets
• A thorough inspection is essential to determine rodent activity (location and population numbers) and bait placement technique
• IPM rodent plans need to minimise rodenticide use, improve hygiene levels, harbourage reduction and include rodent-proofing.

We still need ‘baits’ (the collective term) to control many active rodent infestations. In the eyes of many customers, not using bait to control rodents is, frankly, ‘not professional’.

Considerations

What ‘bait’ do we use? We have various conditions, such as not using bait beyond 35 days, but this doesn’t impact the bait used. This is down to the site assessment and skill of the operator, which is why we're the professionals in the customers' eyes.

Before any control options are deployed, either bait or physical, we need to complete site assessments. Let’s put our actions and activity risk assessment to one side for a moment (but not ignore them, obviously!).

Operationally we need to complete a CoSHH assessment to consider the human elements within the location being treated (often resulting in the decision to simply ‘put it in a box’, which raises another question around safety versus efficacy (but we’ll save that for another time).

Next, we have to think about an environmental risk assessment based on non-targets and ‘potential impact’. The potential impact raises more questions and is increasingly a new area for the pest management professional (PMP) to understand, but more importantly, demonstrate as part of the use of rodenticides.

Pick your poison

In the good old days (around a decade ago), the use of bait was relatively simple: indoor-only (for the more potent, single-feeds) and indoor/outdoor (for the multi-feeds). Though, in reality, how many people used two different rodenticides?

“That’s more containers in the vehicle” was an often-overheard negative point of view. Operationally, we understand why you might choose only to use one bait. Multi-feeds were the most common usage as they could be used ‘anywhere’, so why have two different rodenticides?

For over 50 years, the vast majority of rodenticides available contained one anticoagulant, being either multi or single-feed. Who had really heard of secondary poisoning? And as for resistance, these weren’t mainstream topics.

However, these are topics that, in today’s world of assessments and due diligence, are something service operators do need to consider and think about each time we reach for a ‘bucket of bait’.

Language like ‘first generation’, ‘second generation’, ‘multi-feeds’ and ‘single-feeds’ just confuse the issue for the traditional approach of applying bait.

For over 50 years, the vast majority of rodenticides available contained one anticoagulant, being either multi or single-feed. Who had really heard of secondary poisoning? And as for resistance, these weren’t mainstream topics.

Helen Ainsworth, BASF

However, as the understanding about ‘potential impacts’ becomes more commonplace, the need to understand which bait is used, where and why, is part of efficient rodent control.

The world isn’t moving backwards, these terms are here and understanding them is part of the armoury of due diligence for professional pest control services.

A thorough inspection is essential to determine rodent activity (location and population numbers) and bait placement techniques. Continual assessment through the campaign is
also best practice.

Saturation/surplus baiting

Saturation (aka surplus) baiting is used for multi-feed anticoagulant baits. This process requires the rat or mouse to feed ‘multiple’ times to ingest a lethal amount of that bait. The cumulative effect of these baits builds inside rodents every time they consume the active.

Therefore, to facilitate this multiple feeding, a ‘surplus amount of the bait’ is required to be always available at every bait point so that when the rodents eat, they eat a multi-feed bait. The problem is that so could non-target species, such as field mice.

However, the lower potency, compared to baits used for pulse baiting, was seen as a ‘benefit’ in terms of non-target primary poisoning.

The problem is that larger quantities needed to be available as this is required for the target rodents!

The number of baiting points always needs to reflect the size and location of the rodent infestation.

However, with saturation baiting, the bait point sizes need to be larger, typically up to 200g* for rats. Plus, bait replenishment needs to be undertaken more frequently to ensure that a surplus amount of bait is always in place.

The number of baiting points always needs to reflect the size and location of the rodent infestation.

Helen Ainsworth, BASF

More frequent follow-ups should be undertaken because, if the bait runs out, the rodents will not only find an alternative food source, but they won’t have ingested a lethal amount.

So the whole process starts again, but this time over multiple generations of rodents! This is also a contribution towards resistance.

Multiple follow-ups cost more money as more site visits are required. And time is the most expensive component in most pest control operations.

To overcome this, a common approach was to apply more bait and in longer-lasting formulations to support the length of time in between site visits. Those days are certainly well behind us now.

Pulse baiting

Pulse baiting is used for single-feed rodenticide baits. Considering they have higher toxicity, a rat or mouse can eat a lethal amount of that bait in a single feed.

A significant advantage with this approach is that the bait point sizes for single-feed baits can be smaller, eg 50g* for rats.

How does this affect our approach? We have less rodenticide in the local environment (minimising the potential for non-target primary poisoning), albeit while using a ‘stronger’ active.

This strategy also changes the service approach that PMPs can deliver as part of the eradication campaign, as there may be times when no bait is at some of the bait points.

Considering the ability to achieve a lethal dose in a single feed, why would larger quantities need to be applied? This reduces the potential quantity of rodenticide within the wildlife food chain.

Helen Ainsworth, BASF

Considering the ability to achieve a lethal dose in a single feed, why would larger quantities need to be applied? This reduces the potential quantity of rodenticide within the wildlife food chain.

Yes, some rats may not eat bait during this initial period. However, during the subsequent follow-up on day four*, baits can be replenished, and a smaller volume will be required as fewer rodents will be present.

Repeat* on day seven and every seven days, even if the bait is all consumed by the rodents before the next replenishment is due, that is, let the bait ‘run out’. At each visit, re-assess the site and remainder of the infestation.

With both surplus and pulse baiting techniques, rats remain active from initial bait feeding until the start of potent effects (usually three to five days). With each technique, there remains a risk of secondary poisoning.

Hence the need to search for dead and dying rodents and baiting periods of around three to four weeks are typically required to control a rodent infestation.

Speed baiting

Only Selontra® enables this novel and a highly effective new baiting procedure to be applied.

You can minimise rodent activity around a site after 24 hours (with death occurring after two to five days), and even large rodent infestations can be controlled within as few as seven* days.

All these significant advantages reduce rodent sightings by the customer. It decreases the possibility for damage to occur or disease to spread.

Notably, it lessens the potential for secondary poisoning, as the rodents are inactive 24 hours after eating a lethal amount of bait.

Speed baiting also requires less rodenticide to be applied as part of the eradication campaign, as the rodents will lose their appetite a day after eating a lethal dose and so stop feeding.

This minimises the take of the active ingredient and greatly reduces the potential for multiple-lethal doses, meaning there is less rodenticide in the dead rat.

This also means that less bait needs to be applied, minimising the treatment costs.

Speed baiting also requires less rodenticide to be applied as part of the eradication campaign, as the rodents will lose their appetite a day after eating a lethal dose and so stop feeding.

Helen Ainsworth, BASF

It’s an environmental benefit both in terms of reducing the quantities applied and the residues within the local environment. Selontra also overcomes resistant rat infestations, so this is an effective solution throughout the UK.

The unique combination of the stop-feeding effect and high palatability of Selontra® combine to make speed baiting a key strategy in controlling a rodent infestation within as few as seven days.

*Always read the product label.

Watch this space

Having taken us through the basics, Helen will be back next issue to go into a bit more detail on rodent baiting strategies. Keep your eyes out for PPC105 this winter.

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Source: PPC104