Four more properties in the Top End have been found to be growing banana plants, inside the Banana Freckle quarantine red zones.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 7 minutes 5 seconds 7 m Willem Westra van Holthe and Kevin Cooper speak about the Banana Freckle fines. Download 3.2 MB

Three people have been fined for knowingly cultivating the plants.

If follows the fining of an elderly couple in Darwin's northern suburbs in September for a similar offence.

The discoveries have the potential to seriously set back the eradication efforts of the disease, according to the Northern Territory Department of Primary Industry.

Minister Willem Westra van Holthe said it was disappointing to have people harbour plants, despite the warnings.

"There have been a few recalcitrants out there," he said.

"People who are doing the wrong thing, and there are a few of them, really place in jeopardy the Banana Freckle program.

"It certainly may delay replanting which is due to start in May 2016."

NT coordinator for the national Banana Freckle eradication program, Kevin Cooper, said almost 10,000 properties were re-checked in the second phase of the operation.

He said the plan remained on track, despite the discovery of the plants in red zones.

"There's a resolve across Australia that supports the Northern Territory to get the job done," Mr Cooper said.

"All it's really going to do is slow it up a bit."

Large road signs will now be erected at the Western Australia, Queensland and South Australian borders, to warn any travellers about the banana plant quarantine zones.