Pest control is like lawn mowing – Brent Beaven, PF2050

Brent Beaven —  09/03/2021

Occasionally, you may hear someone say: ‘1080’s not working. We’ve been using it for 60 years, and we’ve still got possums’. Which might sound like a fair comment, but it fails to recognise a crucial reality: pest control and pest eradication are two very different things. This is the fifth blog in Brent’s PF2050 series.

By Brent Beaven, Programme Manager Predator Free 2050

Brent Beaven and tīeke/saddleback
📷: Peta Carey

Pest control is a bit like mowing your lawn: you don’t intend to remove the grass entirely — you just mow it regularly to stop it getting away on you.

Around one-eighth, or 12.5%, of the public conservation estate receives pest control in any given year, and sites are treated at intervals calculated to stop rats, possums and stoats reaching overly destructive numbers.

In forests with lots of food, which support high pest numbers, that might be every three years or even sooner. In less productive forests, that might be every five years.

Beech Forest, Milford Track
📷: Keri Moyle

Now imagine for a moment that you only mowed one-eighth of your lawn once a year, and that you mowed a different eighth each year. What would the grass on the other seven-eighths of your lawn do under such a regime?

This why we still have possums, despite decades of 1080 use.

Sticking with the lawn analogy for a bit, we all know that mowing is a bigger job in the spring and autumn, when conditions are right for grass to thrive.

Similarly, conditions in the forest occasionally become ideal for pests — times when there’s so much food around that they can breed up to their maximum potential. Periodically, whole forests simultaneously produce vast amounts of flower and seed, a phenomenon ecologists call a mast.

For example, when beech trees experience a cool summer followed by a warmer one, they can litter the forest floor between March and June the following year with up to 50 million seeds to a single hectare, many times more than usual.

The magnitude of masts varies across locations and from year to year, but in 2019, beech trees masted pretty much everywhere. So did podocarps — rimu, tōtara, kahikatea, mataī, etc — and in some places, tussocks, in what ecologists called a ‘megamast’.

In times of such abundance predator numbers go through the roof, and that has dire consequences, because once all that seed has either been eaten, or has germinated, plagues of hungry pests need something else to eat. They turn on native wildlife, often just when birds are trying to breed.

Mast seasons come along, on average, every four or five years.

Predator Plague Cycle diagram
✏: DOC

DOC runs a national predator control programme called Tiakina Ngā Manu (formerly Battle for our Birds).

Predator control across large landscapes or remote and rugged terrain costs a lot of money: in 2014 when the Battle For Our Birds predator control programme was launched, it was with a budget of $21 million over five years. Had we met the threat in all affected forests in that period, it would have cost around six times as much.

When a mast loomed in 2017, we had to seek an extra $21m in funding from Treasury to blunt the impact of the mast in addition to the initial five year funding package.

In 2018, within the context of the recently adopted Predator Free 2050 goal, the government increased the budget for Tiakina Ngā Manu to $81.2 million over four years, recognising an ongoing programme of predator control was needed in areas with high ecological values. The programme juggles resources when mast years occur to meet immediate needs while continuing to protect highly threatened native species populations in key areas.  

Which is all to say: possums, rats and stoats are costing the country a small fortune.

Willowbank kiwi chick
📷: Sabine Bernert

It’s estimated that invasive predators do more than $450m of damage to the crop and timber industries each year (as laid out in a 2015 BioScience paper). But arguably the biggest toll never appears in the Treasury ledger: Landcare’s John Innes has estimated that every year they devour around 26 million native forest birds chicks and eggs.

Just like mowing lawns, pest control is a job for life — a never-ending game of whack-a-mole that can only ever hold a line in the sand.

Imagine instead if we could rid Aotearoa of stoats, rats and possums completely — forever.

Picture a forest where a mast season was a bonanza for native wildlife, instead of a disaster.

Kākāriki on Enderby Island, Auckland Islands
📷: Jack Mace, DOC

That’s the proposition of Predator Free 2050 (PF2050), but eradicating pests is a whole other magnitude of difficulty and expense.

Back in 2008 I was working on Rakiura/Stewart Island, and did a study on the potential to eradicate invasive predators from the island. At the time, I estimated it would cost between $35 and $55 million to remove invasive predators from Rakiura/Stewart Island alone. That’s between $210 and $330 a hectare, as opposed to aerial pest control, which can cost as little as $20 a hectare.

It sounds expensive, until you factor in the perpetual price of having these predators in the country. At some point, PF2050 would start paying for itself.

So how much would it cost to eradicate predators from all of Aotearoa?

Even if we apply the highest known per-hectare cost — $993 per ha on Rangitoto and Motutapu Islands in the Hauraki Gulf — and a long-run inflation rate of 2.55%, the bill for PF2050 has been calculated at a little over $9 billion over 50 years.

New-generation traps and detection devices are already bringing that cost down, because they reduce labour. By way of comparison, control agencies expect to spend about $15 billion just trying to contain — not eradicate — all known agricultural pests over the same period.

Kākāpō chick in Invercagill. There are only 208 kākāpō alive today.
📷: Liz Carlson

When they deducted the known costs of invasive predators in New Zealand, and added the expected hike in tourism spending that being predator-free would bring, the authors of this 2015 paper found that PF2050 would deliver a net value of $9.32 billion over 50 years, well into the profit side of the ledger.

We’re not yet able to say conclusively how much it will cost to achieve Predator Free 2050 — and that’s mostly because we’re putting a focus on developing the technology and exploring new innovations that will allow us to do the job. Once we are further down the path with this tech, we will be able to cost it.

That said, some things, though, are beyond price: the greatest value of all would come from saving our native biodiversity from extinction, having it thrive, and for our children’s children to be able to experience it.

Doing nothing would be far too costly.

Ngā mihi

Brent Beaven

For more about the PF2050 strategy, including a run through of the tools that are going to get us there, visit

15 responses to Pest control is like lawn mowing – Brent Beaven, PF2050


    Enjoyed this read, Brent. The cost of doing nothing is immeasurable.


    I like most of the comments above despise 1080. I have used it in Australia and you have to jump through hoops to get it to control Foxes. You have to physically mark where you put a single bait which has to be “buried” (from memory) 150 mm deep away from any water source, then they can only remain there for 48hrs after which any untouched one’s are uplifted and properly disposed of. Some Australians would love to be able to aerial spray 1080 everywhere. But thank God there’s not many of them. Perhaps the dumb ones have moved to NZ. !!!
    Wake up people.

    Regards Russ Hearn

    George Robinson 12/03/2021 at 5:15 pm

    You are totally deluded, stick to mowing your lawn. Your quoting so much doc propoganda that I know you are a lost cause. You simply just have no idea what you’re talking about.

    Bob Williamson 11/03/2021 at 9:41 am

    Interesting analogy ,mowing one eight of the lawn every year would serve to increase photosynthesis in the remaining seven eights .Increasing SOM, microbial soil life ,soil water cycles ,and carbon sequestion .More food for the insectivores,and generally improve the habitat for all life. Perhaps the willingness to use the analogy in this context highlights the singular thinking that is predator free ?


    Whilst I discovered Brent in person was approachable and like able, I would ask him to provide details of a 2020 aerial application that cost the State $20 per ha all costs included, that also meet the implementation targets set. I would encourage Brent to show the public the level of support given to new emerging solutions to aerial delivery where a person can walk, enviroMate100 can reach targets economically and effectively, though this technology spent the last 6 years awaiting DOC to catch up! This is really hard for non funded business to maintain technology production where no DOC / predator Free 2050 Ltd media exposure has been provided and work opportunity was deliberate removed since 2017. Business can not further product research if all performance contract funding is shelved. Whilst Brent my not be responsible directly for such politically directed impediment he has no reason not to disclose the reality that other management systems are and have been around for some time that can target and manage pest population in a “decline to nil approach”. So after 10 years of Eco-land Ltd commitment to delivering economic and effective pest control some of your Predator Free 2050 teams support would be welcomed! It’s a shame the enviroMate100 purchased by Predator Free 2020 Ltd has only delivered lollies at an office desk until the $2 battery died after approximately 13 months……!


      I second the request for Brent Beaven ” to provide details of a 2020 aerial application that cost the State $20 per ha all costs included, that also meet the implementation targets set.”


    Beaven is the heavy duty grim reaper to sentient life forms in NZ. It’s like he has extreme OCD over the dishwasher of life. “You can’t put that there!” He doesn’t get that it all put itself “there” or “here” at some point. And ecosystems are dynamic; ever changing. They are not a diorama. Never static. It’s just not healthy. Neither is comparing indiscriminate aerial poisoning to mowing a suburban lawn.


    What a one sided report. 1080 kills everything, plus what about the long term left overs. Once its dissolved in water, it goes into the roots of the plants and is stored in the plants that either get eaten by birds, fish or will compost back and poison the soil. What about the 2nd degree kills, owls eat poisoned mice etc. And all those poor farming families that live on land where drops go into their water supply. I don’t get it it is such an unfair, hurtful and mean choice. Why on earth would you even compare it with mowing grass….makes no sense at all.

    Neville Du Fall. 10/03/2021 at 8:33 pm

    “Pest control is a bit like mowing your lawn: you don’t intend to remove the grass entirely — you just mow it regularly to stop it getting away on you.”
    Not accurate Brent because unlike mowing ones lawn and managing its growth year on year on year, DOC’s strategy is not about mowing the grass, it is about exterminating anything that is non native from our forests by any means possible and as cheaply as possible and attempting this currently using 1080 Poison, which itself is a non native, man made chemical being introduced and spread over our forests.


    Good explanation Brent, would be great to have a rational online discussion about this. Cheers, Norm

    Noelyn Gordon-Glassford 09/03/2021 at 12:45 pm

    Keep up the good work Brent, our precious indigenous forests and wildlife need it!!

      Tanya mitai 13/03/2021 at 5:50 am

      Our precious wildlife & forests need ‘our’ government to stop poisoning!! Full stop. Remember that the government is meant to ‘govern’ for the people, not go ahead with their outrageous helicopter drops that can not even (and are not) monitired, to give all a realistic update on the how, when, why of all this rubbish. Im sure Sir David Attenborough would have a fair amount to say about it..if he knew the extent that Predator free 2050 is going to have on our country. Wake up nzders..we will run out of time


    Brent, there is no worth-while question to which the use of deadly poisons such as 1080 is the answer. Every time I hear those helicopters flying around my home my heart sinks at this demonstration of callous ignorance. Using such poisons, over and over, in a self-titled war against Nature (now sanitised to some flowery Maori kupu taken out of context by the pakeha system ), bears no comparison to mowing lawns. And mowing lawns isn’t such a good thing to be doing anyway. Is it?
    As for ascribing a cost of $450 million to the ravages of so-called pests, that’s standard rhetoric for the pest industry..It is one of many imaginary figures drawn from mid-air and used to blame whatever animal, so that the real costs of pouring money down a poisoned drain seem some how justified.
    Monetarisation of nature is to be avoided, yet many people have become millionaires from the pest industry that seeks to wipe out all New Zealand most common wild animals. (The only value wild animals are seen to have is the money to be made from their killing)
    Its a sad sad space this country finds itself in.
    A new view of nature and man’s creative, not destructive, role in it is needed. Badly.
    Right now .
    As just one start point I suggest reading A brief history of everything by Ken Wilber.
    (there are no similar philosophers espousing more and more death is there?)
    It would be great to see some honest and open discussion come out of a Department that has long-since closed the doors on a mind made up from historical errors and empire building.
    As for the billion dollar pest industry iit is unfortunately bound to a concrete path and dare not set foot on a lawn, mowed or otherwise.


    You fail to comment on the destruction of the Kea’s in their areas where they live and breed, and where they are being destroyed by the continued plunder of 1080 over their habitat. It kills everything that consumes it.


      The unfortunate death of Keas has been acknowledged several times over however overall it has been widely acknowledged that in spite of the deaths survivability of fledglings has increased as a result of predator control