Alternate to Brodificoum

[Paul Quinn]

We are wanting to move away from using brodificoum in bait stations.  We use it principally for ongoing mouse control or in reaction to rats which may enter during a fence breach.  We have found it to be an excellent poison, but we have been using it for too long and are worried about bioaccumulation.

From the research I have done so far, it appears that diphacinone is the next best thing.  It doesn't have the bioaccumulation problems and isn't really water soluble - so good around water ways.  Its not brodificoum, but it still works. 

Most of this research has been on line.  I am interested in any experience people may have had in the field, especially for using diphacinone to control mice.  I am also interested if people have had success with other toxins in controlling mice.

Cheers.

Paul.

[Dave Houston]

This reply via the DOC animal pests list ...

Not much is available for mice I'm afraid. We have had Maungatautari Ecological Island Trust looking for similar options and a review of labels/registrations shows most are not registered for mice. The only other one accepted for use by DOC staff is Rid Rat Super Wax Baits containing bromadiolone (also a second generation anticoagulant, but not as persistent or strong as brodifacoum).
 
There are other baits registered for rats, but they have either been proven to be ineffective (typically show as prohibited on the DOC status list) or they have not yet been assessed.
 
Mice are tough.
 
Andrew Styche

[Steptoe]

A ramp and bucket of water with polysytrene balls flating on it...and a nice bait on a bigger block in the middle.
And old hot rodders mice trap trick, tried and true for storing cars over winter months.
Just make sure the bucket is not left too long...smell

Will work with rats intially but the get wise to it very quick.

[Dave Houston]

Here are extracts from an internal DOC publication "Choose your control method" for rats.  There isn't one for mice.

First Generation anticoagulant
First generation anticoagulant pellets, blocks or pastes are placed in the bait station. First generation anti-coagulants currently registered for rodent control are:

• Coumatetralyl – Racumin Paste, No Rats & Mice Weatherproof Blocks, No Rats Bait Stations.
• Diphacinone – Pestoff Rat Bait 50D, RatAbate Paste, Ditrac All-Weather Rodent Block.
• Pindone – Pindone Pellets

Pre-feeding is not required and first generation anticoagulants have a shorter persistence time than second generation anticoagulants in living tissue.

When:
Best results at medium to low at densities, but can be used for control at high rat densities with good planning. When an acute toxin has already been used and you want to continue rodent control.

Potential issues:

• There is the potential for poor kills if inadequate amounts of bait are used because rats need multiple feeds to ensure a lethal dose.
  
• Incorrect usage (e.g. frequent sublethal exposure) can lead to resistance to first generation anticoagulants developing in a rat population.
• Possums must be controlled prior to, or concurrently, when using first generation anticoagulants to control rats. Possums are relatively resistant to first generations anticoagulants and are capable of eating large amounts of bait. This will reduce the availability of bait to rats.

Second generation anticoagulant
Second generation anticoagulant pellets or blocks are placed in the bait station. Second generation anti-coagulant rodenticides currently registered for use on the mainland of New Zealand are:

• Brodifacoum: Pestoff Rodent Bait, Pestoff Rodent Blocks, Talon, Talon Rat And Mouse Pellets;
• Bromadiolone: Contrac All Weather Blox, Bromard, Bromatrol, Rid Rat Super Wax Baits, Squeak Super;
• Difethialone: Baraki Rodenticide Pellets, Baraki Rodenticide Wax Block;
• Flocoumafen: Storm, Storm Secure, Stratagem.

Pre-feeding is not required and it is very effective at reducing rat numbers.

When:
To prevent possible accumulation in the food chain, DOC's policy is that second-generation anticoagulants can only be used on public conservation land (excluding offshore islands) for operations that:

• target rodents only;  AND
• use captive baits in bait stations designed to exclude other animal pests present (especially possums);  AND
• where pigs cannot be exposed to the toxin.

Potential issues:

• Long half life so persists in living tissue.
• If resistance to second generation anticoagulants occurs, the resistance cannot be overcome by first generation anticoagulants.
• The technique cannot be used in areas where pigs are present.

1080 cereal pellets
1080 cereal pellets are placed in a bait station following prefeeding. 1080 rodenticides currently registered for use are:

• 0.15% 1080 Pellets
• 0.08% 1080 Rodent Pellets

This method has proven efficacy and can achieve a rapid reduction in rat numbers once the toxic bait is put out.
When:
Particularly suited to controlling rats at high densities or when moderate to high possum numbers are present in the block in which you want to control rats. During long term rat control operations where different toxins are alternated to prevent bait shyness and toxin resistance.
Potential issues:

• Rodents develop acquired aversion to acute toxins, baits and lures if they receive a sublethal dose of the toxin and illness has followed. This can be present for up to 12 months. This means that 1080 cannot be used continuously to control rats.
• If not enough prefeed and toxic bait is put out, possum competition for bait can reduce availability of bait to rats.
• Dogs are highly susceptible to 1080 (in baits and carcasses), meaning the method may be incompatible with other conservation work and adjoining landowners dogs need to be kept under control.

Trapping
Rats are caught in some sort of device, designed to kill the animal, which is set under a cover.
When:
Traps are suitable for continuous rat control at low to moderate rat densities. They can also be used in areas where rats have become poison shy/resistant to toxins.
The public often has fewer concerns about the use of traps compared to many toxins.
Potential issues:

• Periodic control using traps is less cost effective especially when initial rat numbers are high or rat numbers increase rapidly. In years of very high rat numbers, trapping will need to be intensified or a toxin used to achieve an initial knockdown of rats.
• Logistics can become difficult to manage in rugged terrain or large areas.
• Set up costs for trapping can be expensive.
• Daily checking of traps is required to obtain a rapid reduction in numbers.
• No long life baits available, limiting the length of time between checks.
• Pig and possum interference can be a problem.
• In beech forests during years with high mouse numbers, mice taking the bait or being caught can severely reduce the effectiveness of traps.

[Dave Houston]

... and this from Graeme Weavers

In Whirinaki we have had very good results with Diphacinone. We target rats & don’t have data on mice except what we see as a comparison from our non-treatment to treatment tracking tunnel results, & they show extremely low mice in the treatment tunnels i.e. occasional mouse will show up (usually toward the end of the season) compared to a few regularly in non-treatment. We may not have great mice numbers as we have big numbers of stoats & more numbers than we would care to notice of feral cats. We have high pig numbers that come back after control but in the last season had no Diphacinone predation by pigs. We have used Diphacinone for around 7 years & have no indication of tolerance or shyness. We have gone to Pindone this year due to label restrictions, but if they are resolved will go back to Diphacinone with a break season every few years to another product; either Pindone, depending on pig predation & other secondary poisoning & flesh sampling results this season or Coumatetralyl which we are using this year in two small kokako areas. If it works well we may use that as an alternative to Diphacinone when we give it another break. Carcass breakdown is usually noticed at around 30 days, even though our signage is still for 3 months minimum, so gives some assurance (their own choice & risk !!) to hunters with dogs that carcasses are not still available.

[Alicia Warren]

I used diphacinone continuously (monthly) over 2 years to control rodents along a waterway.  I got excellent rat control and initially excellent mouse control but after the first year I got increasing abundance of mice.  I appear to have created a mouse population with resistance to diphacinone by using it continuously for 2 years.  I dealt with this by using a pulse of bromadiolone.  Hopefully I can go back to using diphacinone now but I will increase the intervals between its use.

DOC recommends using first generation anticoagulants as pulses rather than continuously, to reduce the chance of developing a resistant population; i.e. keeping bait stations full for at least 5 days and perhaps up to 2-3 weeks and then removing the bait at the end of the pulse and doing this up to 4 times a year.  The other thing to do if you are doing 4 pulses a year is to use a second generation anticoagulant in every 4 to 8 pulses to deal to any resistance to first generation anticoagulants that might be building up in the population.  Although this doesn't remove the use of 2nd gen anticoagulants it does minimise it.

Alicia