4.3 How 1080 is used

1080 Products

1080 is manufactured in the USA and imported to New Zealand for formulation into 1080 products. Although most people think of 1080 in terms of the baits used for possum control, it is also used in a variety of different products, to control pest species ranging from wasps to goats. Table 2, shown below, lists 1080 products, the target species and the different situations in which they are used.

Table 2.
List of 1080 products and uses

1080 product	Target species	Use
Cereal pellets	possums, rodents, rabbits	Tb operations, conservation land
Carrot baits (sprayed with 1080 solution)	possums, rodents, rabbits	Tb operations, conservation lands
Pastes	wallabies, possums, goats, rabbits, wasps	conservation lands
Gels	feral goats, deer, wallabies	conservation lands
Fish-based pellets	feral cats	conservation lands, island eradications

Cereal-based pellets are manufactured by compressing a mixture containing bran, kibbled grain and sugar, along with 1080, green dye and flavouring such as cinnamon. The green dye reduces the attractiveness of the baits to birds and the flavouring masks the odour of 1080 to possums, as well as deterring birds. Cereal baits are often preferred because they have a reasonably long shelf life, are easily handled, have a consistent amount of 1080, and degrade rapidly in the environment. Pellets are made in sizes ranging from 2 to 12 grams, and typically contain 1080 at a concentration of 0.15% (1.5 milligrams of 1080 per gram of bait).

Carrot baits are prepared just prior to use. Special cutting equipment cuts carrots into cubes weighing about 6 grams. This size makes them too big for most non-target species. The baits are sprayed with 1080 solution to give a concentration on baits of either 0.08% or 0.15%, the same concentration as used in pellets. Carrot baits are also dyed green and given an added flavour, both to deter birds and make the baits more palatable to possums.

Pastes and gels are also dyed green and masked with flavours such as cinnamon. Pastes are usually applied in bait stations or on raised earth "spits" (clods of earth). Any spits remaining after a certain period are overturned to bury the bait before stock are put back into the treated area. Soil microbes rapidly degrade the 1080 on the buried spits into harmless by-products. Some pastes are designed to be applied to leaves, so that pests such as goats can be targeted.

Research trials have shown that 1080 solution injected into hen eggs, which are then placed in special bait stations, can reduce stoat populations by about 90% within 22 days. Poisoned hen eggs have been used by DOC to control stoats in the Boundary Stream and Hurunui "mainland islands"³¹.

Aerial operations

During aerial application of 1080, bait is spread using custom-designed bait applicators incorporated into modified top dressing aircraft or suspended from helicopters. Over the past 25 years, there has been a significant reduction in the amount of bait distributed per hectare (sowing rates). Over this time, sowing rates have declined by a factor of over three for both carrot and pellet baits (see Figure 5).

Figure 5.
Trends in aerial application rates of carrot and pellet baits
[Reproduced from: The Brushtail Possum, Page 146, Manaaki Whenua Press, Lincoln]

Pellet baits that used to be spread at a rate of 20 kilograms per hectare are now spread at 3-5 kilograms per hectare, and sometimes as low as 1-2 kilograms per hectare. Sowing rates of 3-5 kg/ha are now standard practice in aerial 1080 operations, for both carrot and cereal baits. For baits weighing about 6 grams, the range of sowing rates results in the distribution of about 830 baits per hectare (at 5 kg/ha) or 160 baits per hectare (at 1 kg/ha). In recent years there has been a move to larger baits of 12 grams, which further reduces the number of baits distributed per hectare. The reduced sowing rates have reduced the costs of operations and have lowered the risks to non-target species by exposing them to fewer baits and less poison.

Less bait

Why are fewer baits and less 1080 now used per hectare in aerial operations? A common reason for possums surviving aerial operations used to be due to poor bait coverage, meaning large areas within the treatment area might be missed entirely and receive no baits at all. Pilots now use global positioning systems equipment that allows them to track their position very accurately while flying. This has led to a marked increase in the accuracy of the bait coverage. Improved bait quality has also meant fewer baits are needed per hectare. Further reductions are constantly being sought through improved bait-spreading machinery.

The application of baits containing 0.15% 1080, at the rate of 5 kg per hectare, means there will be 7.5 gm of 1080 (about 1.5 teaspoons), distributed per hectare. At 2 kg of bait per hectare, the amount of 1080 per hectare drops to only 3 gm. (less than a teaspoon). Nevertheless, there is always a need for a very high level of quality assurance in all phases of aerial control operations. Current procedures for using 1080 are described in Chapter 4.4.

Ground operations

In ground operations, 1080 is used in the form of pellets, paste or gel in bait stations, or as paste baits on the ground or in bait stations. Bait stations are commonly used where it is important to avoid exposing livestock, people, pets, or native animals to the toxin. Large bait stations can hold over a kilogram of pellets, which means that numerous possums or other pests can feed at each station over a period of days or weeks. When pellets are protected from rain they can last up to five weeks, compared with their deliberately short field-life when spread by air. Bait stations can be placed on trees out of the reach of many non-target species.

1080 paste is often used for ground control of possums. Paste made from apple pulp, invertase sugar and water, usually also contains cinnamon oil as an attractant or lure for possums, and a mandatory green dye to deter birds. Stock is usually taken off the control area. Paste bait is applied using an applicator gun onto upturned earth "spits", into small bait stations or onto retrievable cardboard squares or tin lids. Where possum numbers are high, as is often the case on farm/forest boundaries, baits may be replaced over several days before the spits are turned back to bury the residual paste, or bait stations emptied, and cardboard squares or lids retrieved.

Cereal 1080 pellets and carrot baits are occasionally spread by hand in small forest areas, where access by livestock and the public can be controlled. In all ground-based control it is important to prevent bait-shyness from developing in the possum population, by not using the same bait for too many poison cycles. This is achieved by changing the way the poison is presented (switching from pellets to gel) or by changing from one poison to another, (from 1080 pellets to cyanide, or vice versa, for example).

By air or by ground?

Management objectives, priorities, budget, risk management and cost-effectiveness all influence how control agencies use 1080.

The major user of 1080 is the Animal Health Board, for the control of vectors of bovine Tb, usually possums, followed by Department of Conservation, for the protection of native plants and animals from a number of pests. Regional councils prepare regional pest management strategies under the Biosecurity Act 1993, and some regional councils use 1080 for pest control, although their use would be significantly less than either the AHB or DOC. (Some regional councils also undertake or manage control operations under contract to the AHB.) A much smaller amount of 1080 is used by other sectors, mainly the forestry sector, to control possums around areas with new pine plantings.

The different objectives of the AHB (controlling Tb vectors) and DOC (protecting conservation values) mean that they use different mixes of methods to achieve their objectives.

In Chapter 3, it was noted that AHB operations tend to comprise initial reductions (often involving large aerial operations as well as some ground control) followed by a second, maintenance phase, which tends to use more ground control. When DOC is controlling possums over large areas, it tends to favour aerial 1080 operations, particularly when the terrain is difficult and/or remote, and where there are other pests present. Even successful aerial operations need to be repeated at intervals of about eight to ten years to prevent the subsequent possum build-up from threatening conservation values. For some pests, however, DOC might rely on 1080 used in different products applied on the ground. This is the case for wasp control in beech forests, wallaby control, as well as possum and predator control in many accessible areas where bait stations are an effective and efficient technique.

Many possum management actions are designed to reduce possum densities to a 5% residual trap catch, that is, no more than five possums caught per 100 trap nights. In all cases, the choice of application method is influenced by the total area to be managed, terrain aspects, accessibility of the area, the initial density of possums and the cost, which is affected by all of these factors. The main contributor to the cost of an operation is the cost of labour. The longer it takes to get possum populations down to the desired density by hand, the more the labour costs will increase. Difficult terrain and access limit the area one person can work in a day, which drives up the costs. Sometimes areas can be close to farmland and still be very difficult to work by hand. For example, dense undergrowth can be as problematic as cliffs. At the same time, aerial 1080 operations cannot be used in many farm areas because it is not possible to de-stock the area completely. Figure 6 shows that, in general, the trend is to use aerial operations in more difficult country, well removed from human settlements and agricultural activities, and to use ground-based application in more accessible country.

Figure 6
Trends in 1080 application methods

Diagram key:

	Pasture
	Forest margin
	Back country
	Increasing use of ground-based application
	Increasing use of aerial operations

While the actual proportions of ground versus aerial application vary from year to year as objectives change, 1080 remains the only vertebrate poison permitted to be applied by air in New Zealand. A 1978 report on 1080 use reported that 87% of 1080 used was applied aerially ³². Although comparable data is not available on current operations, aerial application is still the major application method for 1080 use in New Zealand. As demonstrated by the application rates, however, the reduced density of application has resulted in more land area being able to be treated by an equivalent amount of 1080. In summary, the aerial application of 1080 is often the only effective way to simultaneously achieve three major objectives:

• reduction of possum densities to below the 5% residual trap catch level

• reduction of pest populations of rats and other predators

• rapid achievement of low possum densities over large areas, which is particularly important to stop new outbreaks of Tb from spreading.

Aerial application, therefore, remains an important tool for all agencies. For all application methods, the need to optimise cost effectiveness and risk management continues to drive the search for better techniques.

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