A significant number of traps had been set in the exclusion zone and were being checked regularly "and still only the one fly had been found".
Asked whether the exclusion zone would be extended, the minister said that until further fruit flies were trapped, there was no reason.
"It's too early to be sure but every day gives us hope it was a single, male fruit fly.
"We will not relax for at least another 10 days until we are absolutely sure that we have not got a fruit fly population established."
Mr Carter said he was not aware of any person in the zone who had disobeyed the ministry requirement not to take out fruit and vegetables.
Checks at the Avondale Racecourse venue yielded only a a few bags of feijoa and capsicum said to have been bought from the Avondale shops.
A woman entering the market munching on an apple put it in the quarantine bin after an official discovered she was from the exclusion zone.
Officers also gave out information flyers with a map showing the zones.
Produce stall holder and grower Tony Zaknic, of Kumeu, said he supported the official's work.
"I see the fruit fly as a big concern and it is good they are taking it seriously," he said. "They must stop this coming in from overseas or a lot of people will go down the gurgler."
But New Lynn resident Thomas Whitmore was surprised the ministry did not have signs on street lamps to alert people.
"I drove down a main street in the exclusion zone and there was not a hint of a sign," he said.
"A 15-year-old with a marker pen and some cardboard could do a better job of letting people know they cannot take out fruit."
When the Herald visited the controlled area one resident was unaware that a baited trap for fruit fly was hanging from a lemon tree in the garden.
Avondale Business Association chairman Duncan MacDonald said the only sign of the emergency prompted by the world's worst fruit pest were three yellow bins in Wolverton St.
He was surprised that the fruit and vegetable section of the market had not been shut.
"A lot of people come from all over to buy their produce here and the market is right on the boundary of the exclusion zone," he said.
"It is running a great risk."
But market operator Rob Kemp said the ministry had been careful. Pig farmers usually took the waste produce, Mr Kemp said, but yesterday officials ruled that all waste must be taken straight to the rubbish dump.