Work to remove rhododendrons which are growing out of control in Snowdonia National Park will cost around £10m and take at least five years.
The plant has spread "like wild fire" and now covers more than 5,000 acres (2,000 hectares) of the park.
Despite an eradication programme, finding the £10m needed to battle the species has been a problem with just £800,000 raised so far.
The plant was introduced by gardeners in Snowdonia in the 19th Century.
Rhys Owen, the park's head of agriculture and conservation, said the rhododendron ponticum species found in Snowdonia thrived in the area and had the ability to spread "like wild fire".
A concerted programme to control the species was launched in 2008 by the national park authority, alongside teams from Natural Resources Wales, The National Trust and Gwynedd council.
Mr Owen said the partnership had raised £800,000 but it was nowhere near the £10m needed to eradicate it.
The worst-hit parts of Snowdonia include Madly, south and north of the Mawddach, the Vale of Ffestiniog, Glaslyn and Gwynant areas, Beddgelert and Betws y Coed.
"If we had a steady stream of funding or managed to raise the £10m it would take at least five years to eradicate the rhododendrons across the park," said Mr Owen. "We have some very fragile habitats and it out-competes everything and smothers everything.
"It even hosts Phytophthora ramorum which is killing larch trees and it can kill animals that graze on its leaves.
"If that's not enough, when rhododendrons flower each plant produces one million seedlings which are spread on the wind."
He added: "We failed to secure EU funding in 2012, but we are constantly looking for new opportunities to bid again so we can solve the problem we have with this plant."
The list was going to be restricted to 50, but will now have no limit. It is not clear which species will be banned.
Mr Owen said it was easy to blacklist invasive species but there had to be money available to back it up.
In its latest battle against the rhododendron, the national park is spending £250,000 trying to control and eradicate it in Nant Gwynant and Beddgelert.