FAQs

Download key facts about possum control operations on the Otago Peninsula here (PDF).

A page of questions. . . .

FAQ: What are the options for control of possums

FAQ: What are the pros and cons of the different toxin options?

FAQ: What makes a good possum bait?

FAQ: How do bait stations work?

FAQ: Possum control using encapsulated cyanide (Feratox)

FAQ: Possum control using brodifacoum poison (Pestoff or Talon)

FAQ: Possum control using Cholecalciferol – Vitamin D3 poison (Decal and Feracol)

FAQ: Possum control using Pindone possum and rat pellets 0.05% (Greater Wellington Regional Council, 2007)

FAQ: What are the potential effects on cats and dogs


FAQ: What are the options for control of possums

Possum control is carried out using a number of techniques. Trapping and shooting are long-established methods of controlling possums. They have traditionally formed the basis for the possum fur industry and, more recently, the possum meat industry. All AHB and many DoC operations are open to tenders using these approaches.

Another method of ground control of possums is laying bait containing 1080 or various other poisons. Ground control is generally used on more accessible terrain where possum numbers are low, as a follow-up to aerial drops or at the borders of sensitive areas such as next to a farm or near water to complement aerial application.

While poisons are currently the preferred option for most possum control in New Zealand, each poison has its own advantages and drawbacks. Brodifacoum kills possums more slowly than other poisons and its tendency to bioaccumulate (build up in organisms) is a major drawback. Phosphorus is seen as less humane than other poisons. Pindone is less persistent in the environment than brodifacoum, but it is also less effective. Cyanide is highly dangerous to human beings compared with other poisons.

FAQ: What are the pros and cons of the different toxin options?

Table 3.1.3 (Beaven 2008: 48): Summary information for toxins available in New Zealand and their pros an cons in relation to eradications (Eason and Wickstrom 2001; Broome et al. 2006; Broome et al. 2006; Fisher and Broome 2006; Fisher and Fairweather 2006; Fisher and Fairweather 2006).

TOXIN
Warfarin, Diphacinone,
Pindone, Coumatetralyl (1st generation anticoagulants)

Trade names: Ditrac,
RatAbate, Pest-Gone,
No Rats, Racumin

Pros
Diphacinone has successfully eradicated ship rats on some small islands.
Readily metabolized.

Cons
Generally require rodents to feed on them multiple times on successive nights to be effective. This would be extremely difficult to achieve.
Only Pindone is currently registered for aerial application.
Significant non-target risks to wildlife and pets.

TOXIN
Floucomafen,
Bromodialone

Trade names: Bromard, Rid Rat Super, Storm Secure, Stratagem.

Pros
Second generation anticoagulants are slow acting allowing secondary poisoning of cats and not incurring bait shyness.

Cons
The effectiveness of brodifacoum in rodent control and eradication operations is better known that for Floucomafen or bromodialone. (There is no advantage in using either of these otherwise apparently suitable alternatives).
Lack of information of the environmental effects of bromodialone and floucomafen.
Not registered for aerial application.
Significant non-target risks to wildlife and pets.

TOXIN
Brodifacoum

Trade names: Talon, Final, Entrap, Pestoff.

Pros
Proven successful in many eradication campaigns.
Well-known effects means clearer idea of the mitigation actions necessary to minimize non-target risks.
Antidote available (pets and humans).
Slow acting allowing secondary poisoning of cats.
Registered for aerial application.

Cons
Significant non-target risks to wildlife and pets.
Can remain in liver of sub lethally poisoned animal for months.

TOXIN
1080 (Sodium monofluoroacetate)

Trade names: No Possums, Pestoff Professional.

Pros
Less risk to non-targets and people as it degrades quickly and is metabolized rapidly.
Registered to aerial application.
Registered for use on rats, cats and possums.
Highly toxic to rats, cats and possums.
Very well studied with large knowledge base developed.
Well known effects means clearer idea of mitigation actions necessary to minimize non-target risks.

Cons
As with other acute (fast acting) toxins, bait shyness is more likely.
Can be detected and avoided by some individual rodents making it unsuitable for eradications.
Significant non-target risks to wildlife and pets.
1080 would not be an appropriate toxin to use on the Otago Peninsula.

TOXIN
Cholecalciferol

Trade names: Pestoff Decal, No Possums.

Pros
Lower risk to birdlife than brodifacoum.
Highly toxic to mammals.
Naturally occurring product (Vitamin D).
Effective treatment for toxicosis available.

Cons
Still potentially lethal to non-targets and likely to cause some deaths.
Unproven in eradications; success in possum control operations has ranged from 63.1%-93.7% reduction.
Not registered for aerial application.
Risk of secondary poisoning to cats considered low.
As with other acute (fast acting) toxins, bait shyness is more likely, making it unsuitable for eradications.
Not registered for use on rats.

FAQ: What makes a good possum bait?

(Beaven, 2008: 52)

Baits are a food package designed to be attractive for the target animal to eat. They are not in themselves toxic, but have the toxin added to them as a way of getting the toxin into the target animal. For example, the bait Pestoff 20R is composed of cereals, sugars, waxes and binders. (1 Ingredient list taken from material Safety Data Sheet for Pestoff 20R).

The ideal bait and toxin combination is: i) palatable and lethal to target species after a single feeding; (ii) persistent in the environment long enough for target species to be exposed; (iii) short enough to minimize non-target exposures; (iv) low probability of engendering bait shyness and (v) non-toxic or non-palatable to non-target species (Howald et al. 2007).

Choosing a bait which is attractive to all target species and which will remain palatable long enough for all target species to consume a lethal dose of toxin is a critical element in successful eradications. The bait in which the toxin is held must be extremely palatable to the target species and must be in a form suited to the method of distribution and presentation. There are several commercially available baits to choose from. Compressed grain pelleted baits have proven to be particularly palatable to rodents in eradication operations worldwide. The advantage is that an adequate dose of toxin is delivered when compared to loose grain, or waxy blocks, which may not result in rodents receiving a lethal dose of toxin. Also, the bait has to be able to go through the machinery (e.g. spinner bucket) and be spread effectively with minimal fragmentation.

Currently, Pest-off 20R, RS5 and Agtech baits are the only effective products available for aerial spread in New Zealand. Pestoff 20R is highly palatable (Morriss et al. 2008) and well proven, having been used in most island eradication operations. Morriss et al (2008) found that weathered bait was less palatable for Norway rats. Therefore, there may be advantages in investigating harder bait that will resist weathering and will also store for longer periods. Bell Laboratories (USA) has developed a harder bait named Brodifacoum 25 Conservation. This bait has been field tested, with good results, for effectiveness on rats and ability to withstand harsh environmental conditions in the Aleutian Islands (Buckelew et al. 2007). This increased time in the environment could also lead to increased potential for non-target effects.

Alternatives could be considered if they met the following criteria:

A.  Bait has proven palatability to all rodent species targeted as well as possums and ideally wild cats.
B.  Manufacturer has a proven track record of quality control at all steps in the manufacturing process
C.  Bait has proven storage life and has been used in conditions likely to be encountered.
D.  There is sufficient information about palatability to non-target species to enable those species at risk to be predicted and the risks managed to acceptable levels.
E.   The bait is logistically and financially feasible to produce.

FAQ: How do bait stations work?
(Beaven, 2008: 58)

Bait station operations involve the establishment of a grid system of stations across the entire area to be treated. Often bait stations are left in position un-baited to allow rodents to become accustomed to them, thereby reducing any initial neophobia before bait is made available. Bait stations are normally loaded simultaneously (i.e. on the same day) with toxic baits and initially replenished daily, always ensuring that bait will be available every night at each station. Some rats and possums may occupy areas around particular bait stations, thus preventing subordinate rats and possums reaching bait. For example, on Kapiti Island, dominant Norway rats prevented subordinate Norway rats or kiore / Pacific rats from accessing bait stations (Bramley 1999). Trials revealed that kiore / Pacific rats would not even use bait stations that Norway rats had used (Cromarty et al. 2002). As a result, bait take may persist for some time after the initial fill. However, once the dominant animals have died the baits become more accessible to others. Bait take may occur over several weeks, even months, before all individuals succumb.

The duration of a bait station campaign depends on various factors, including the density of bait stations and of rodent and possum populations (basically, the more bait stations there are the quicker the operation will be). The correct spacing of bait stations is critical – for rats in new Zealand it appears that grid systems varying between 50 x 50m, 50 x 100m and 100 x 100m are appropriate, depending on the species present (Thomas and Taylor 2002).

Bait stations require intense effort, not only in establishing a track network and putting the bait stations in place, but then regular filling for extended periods. If a 50 x 100m grid was used, at least 400 000 bait stations would be required to cover Stewart Island / Rakiura, with over 20 000km of track network to service them. This number of bait stations would take over 2000 person days for one fill (A. Gutsell, pers. Comm.), making it impossible to replenish all stations on a daily basis. The required track network, aside from the logistics of installation, would cause extensive environmental damage. Due to the size of Stewart Island / Rakiura, it is not practicable to use bait stations over the whole island, but this technique could be employed in localized areas such as the township.

FAQ: Possum control using encapsulated cyanide (Feratox)

(Greater Wellington Regional Council, 2004)

How is Feratox used?
Feratox pellets are made palatable to possums by disguising them in peanut paste blocks (dyed green) or a feed paste. The peanut blocks are put in bait bags and stapled to trees while the feed paste is used in bait stations. Chewing the peanut block will ultimately crack the Feratox pellets and release the cyanide poison into the possum’s system. Bait stations are managed regularly and any pellets to reach the ground “will perish and break down in the soil once wet”.

Danger to humans
Cyanide is fatal to humans. Typical symptoms of poisoning include dizziness, rapid breathing, headache, drowsiness and unconsciousness. In any case of suspected ingestion immediate medical attention is critical as “cyanide is a rapidly acting toxin”.

Danger to dogs and cats
Dogs and cats have a much higher risk of direct poisoning by ingesting cyanide bait than they do of secondary poisoning by eating possum carcasses. Despite this fact, dogs should not come in contact with possum carcasses.

Why use cyanide?
Reasons for using cyanide include its ability to kill possums “on the spot” which also makes skin and fur collection possible; its efficiency in “high possum density areas”; “easy to lay” baits and the “low risk of secondary poisoning”.

FAQ: Possum control using Cholecalciferol – Vitamin D3 poison (Decal and Feracol)
(Greater Wellington Regional Council, 2004)

How is cholecalciferol used?
One 30 gram dose of the green cereal pellets known as Decal is lethal to possums. Bait stations are packed with either loose pellets, plastic bags containing 30 grams of pellets, or a combination of both. Trees are used to anchor the bait and bait stations at a height above the reach of pets and livestock.
Feracol Defenders and Strikers are bait stations containing 100g and 18g of Feracol, respectively. The bait itself is a peanut based paste dyed blue/green. Both Feracol Defenders and Strikers are anchored to trees.
All bait stations and plastic bags are labelled with warning signs.
Cholecalciferol is not water soluble and is sensitive to light, heat and contact with soil, all causing it to break down.

Danger to humans and animals
Cholecalciferol occurs in nature as Vitamin D3, but is still dangerous to humans in high doses. It is important to take precautions by not handling bait, dead possums or rats.
Dogs and cats are at risk of being poisoned from eating baits directly. The risk of secondary poisoning is low, as the poison breaks down in the dying possum, but dogs should not be allowed to scavenge carcasses.
Keeping cats well fed can help prevent them from eating carcasses.

Why use Cholecalciferol?
Possums and rodents are sensitive to calcium, making them susceptible to Cholecalciferol because it raises blood calcium levels, causing heart failure within four to seven days for possums.

FAQ: Possum control using brodifacoum poison (Pestoff or Talon)
(Greater Wellington Regional Council, 2003)

How is brodifacoum used?
Brodifacoum bait pellets are dyed blue and only registered for use in bait stations. These are allocated to one per hectare at approximately 100-150 metres apart. Brodifacoum is available for use without a poison license under the trademarked names of Pestoff and Talon.

Danger to humans
The risks associated with brodifacoum are low when used in the approved manner. A large quantity of the poison must be ingested to cause death (approx. 5kg for a toddler and 50kg for a 70kg adult).

Danger to dogs
Dogs are at low risk of brodifacoum poisoning and would have to directly eat more than 250grams of bait or several carcasses to cause harm. Cats are not interested in the pellets.

Danger to livestock
The anticoagulant toxins of brodifacoum persist in the body for months and possibly years. Any livestock that has been exposed to the poison is not suitable for sale or slaughter.

Danger to feral game
Landowners and hunters intending to sell their game for consumption should not take feral animals “from an operational area within nine months after the termination of poisoning” or “within 2km (5km for feral pigs) of a poisoning operation boundary”.

Environmental effects
Brodifacoum breaks down over time “in soils with pH5.5 to pH8. It is water insoluble and not absorbed by plants, becoming practically inert as it binds strongly to soil.
Because brodifacoum is persistent in the livers of animals, secondary and tertiary poisoning is a concern for other species.

Why use brodifacoum?
Brodifacoum is used successfully

A) To control light and moderate populations of possums.

B)  To reduce numbers to very low levels.

C)  In areas under maintenance control, following initial knock down operations.

D)  For private landowners to take responsibility for possum control on their land.

E)  Bait shyness is not likely to occur due to length of time between ingestion and onset of symptoms.

FAQ: Possum control using Pindone possum and rat pellets 0.05% (Greater Wellington Regional Council, 2007)

How are Pindone pellets used?
Pindone pellets contain 0.5g/kg of Pindone and are packed into bait stations that hold 1-2kg worth. One bait station per hectare can be placed in bush areas and shelterbelts. These stations must be set out of reach of children, pets and stock.

Danger to Humans
Pindone poses little threat to humans in comparison to other vertebrate pesticides, but it is still hazardous if ingested. One would have to eat excessive amounts of bait to result in death. Safety precautions include:

A).  Storing bait in a safe place, away from foodstuffs, children and pets.

B).  Avoid contact with skin.

C).  Wear overalls and waterproof gloves when handling bait.

D).  Avoid contamination of any water supply with baits or empty containers.

E).  Do not eat, drink or smoke while using.

F).  Wash hands and exposed skin after applying bait.

G).  Danger to pets
Although pindone is less potent than other poisons, pets should be kept away from poisoned areas and carcasses as a precaution against accidental poisoning. If a pet has swallowed pindone bait a vet can administer Vitamin K1 in the early stages of poisoning.

Danger to Livestock
Livestock exposed to Pindone should not be sent to slaughter or sold. For livestock and milk production a two month withholding period applies.

Danger to wild game
Any animals exposed to pindone will eliminate any residues within three weeks, but game should not be taken from a treated area for two months after treatment has come to an end.

Effects on drinking water
Pindone is unlikely to have an effect on drinking water as it is placed in bait stations and kept away from streams and waterways.

What is Pindone?
Pindone, an anticoagulant poison used on rodents, wallabies and possums, has been found most useful for rabbit control in New Zealand and Australia.

Further information can be obtained from the National Poisons Centre,
Phone 03 479 7248, or in an emergency, 03 474 7000 or 0800 764 766

FAQ: What are the potential effects on cats and dogs

(Beaven, 2008: 75)

There is some risk of cats and dogs being poisoned through eating cereal baits directly, or of secondary poisoning due to the persistence of brodifacoum in body tissues which may be consumed by these animals. Anticoagulant poisons are slow acting and there is a reliable antidote that is readily available. Although treatment is often complicated, the prognosis for successful recovery is generally good if toxicosis is detected early. Pets would need to be confined or otherwise prevented from accessing bait or rodent carcasses, should an eradication be undertaken. Primary poisoning is probably a greater concern if pets are in an area aerially treated. Secondary poisoning will only be an issue if pets are allowed to roam and scavenge.

Rodent control operations, using similar anticoagulant baits sold “over the counter” have been in place on private land and around houses for over 30 years, apparently with few pet mortality issues. Dog control regulations may serve to limit any potential negative effects of an eradication operation. Nevertheless, the key to eliminating any negative effects for dogs will be adequate education of owners as to the degree and possible mechanisms for risk and treatment coupled with local veterinarians holding stocks of Vitamin K. Temporary additional dog control regulations during and immediately following any eradication will also be useful.

2 thoughts on “FAQs

  1. Committee

    Hi, we recorded around 700 possums killed in 2014, from our work, resident’s trapping, and road kills.

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