"When I drove around the area I started to realise how much privet was growing in our area. It became a personal challenge to see what I could do about it.''
Davies-Colley and his wife, Catherine, have built a successful business, SewEzi, from their invention of a portable sewing table. Their love of gardening has led to their stunning garden of 160 magnolias regularly featuring in fundraising events.
While the privet problem might have overwhelmed many people, Davies-Colley systematically mapped out the area and highlighted areas of privet and the property owners nearby.
"With the map, I was able to see that the privet was mainly in our area of about 2500ha and not too much outside that. That's when I started to believe we could tackle this weed."
He said key to the project was to make contact with landowners based on a non-judgmental approach.
"It's the weed we are targeting, not the landowner. We need permission to access the land and if the owner wants to help, that's great and many do. The Northland Regional Council is available to help with advice and provide chemicals.
"We have multiple owners to large dairy farms as well as Whangarei District Council land and Transit NZ land. We don't place judgment on anyone. Everyone has different priorities and, in many cases, they know there is a problem but it has become something they think is too hard to fix.
"Not everyone is able to help and early on I met an elderly woman who was surrounded by privet and suffered terribly from asthma. It was severely affecting her quality of life and it really brought home to me why the project is so important."
Privet inhabits bush, gardens, roadsides, fenced streams, orchards and any ungrazed areas. It prevents native plant regeneration and can completely dominate areas of bush.
Its strong perfume can contribute to respiratory disorders and can be toxic to livestock.
The yellow flowers of privet will betray its presence over the next few months.
"That's a great time to make a note of where the trees are."
Seeds set in the winter, so if the trees can be stopped from flowering the cycle can quickly be broken.
"It's not like gorse seeds which are viable for many years. Privet seeds are only viable for about two years and we have found the birds don't carry the seeds a great distance, so it is possible to get on top of it relatively quickly if you can break the cycle.''
He said while there were other weeds being targeted, such as mothplant, woolly nightshade and Elaeagnus, it was best to concentrate efforts on one weed at a time.
"It's too easy to get distracted and the job becomes overwhelming.''
After an initial bad start where the recommended spray concentrations turned out to be inadequate, he had now found several good methods which worked well depending on the size of the trees and where they were growing.
"Drilling and frilling" entailed drilling holes in the bark or damaging it with a chainsaw and inserting herbicide such as Metsulfuron, which is also known as Meturon or Escort.
"It needs to be applied at 20g per litre. Essentially we are killing the tree while it is still standing.''
The second method is to "cut and paste", felling the tree and spraying the stump.
For smaller shrubs with multiple stems, spraying is effective at a rate of 5g per 10 litres. Seedlings are easy to pull out by hand.
"It is very important to do follow-up treatments. Otherwise your early efforts can be wasted as these weeds don't give up easily.''
For people who did not want to use chemicals, killing the tree was difficult but still possible by covering the stump to exclude any light.
Davies-Colley said he used all of the methods, depending on where he was working, and was particularly careful around any waterways as the spray was toxic to aquatic life.
One of the most visible success stories has been the urupā (cemetery) at Poroti which was an impenetrable wall of privet trees. Davies-Colley has worked with the administrators of the site to gain access. Native trees are now starting to regenerate and the aim is for it to revert to native forest.
Davies-Colley said weeds do not respect property boundaries so landowners needed to change their mindset from only tackling weeds on their own land.
"It's only when the community works together that we can be successful or you will always have seedlings popping up from next door.''
