A Brazilian couple, who claim chemicals were showered on them while tramping, say New Zealand's "clean, green" image is a joke.

Caroline Leone and husband Rodrigo Ferreira Santos from Sao Paulo saved for their trip-of-a-lifetime to New Zealand because they believed it "was the perfect place for experiencing beautiful nature, amazing national parks and great landscapes".

However, while tramping the Heaphy Track before Christmas they and others were shocked to experience a "rain of chemicals" from a helicopter spraying gorse.

Ms Leone said they were aware of a helicopter and aeroplane flying directly over head for the entire five-hour tramp back to Kohaihai.

They thought a rescue was being staged somewhere, until arriving at Kohaihai they saw a sign advertising aerial spraying of gorse.

"I have no word to describe the anger I feel right now," said Ms Leone who suffers from a medical condition which is made worse by herbicides and pesticides.

"We could not believe what had just happened to us. We find it completely unacceptable and disrespectful as well as a deep violation of our rights not to be told that we were going to be exposed to any chemical spraying whilst tramping in a national park."

Karamea tourist operator Paul Murray, of Rongo Backpackers where the couple stayed, said they were visibly shaken and angry.

He described the chemical applications as "a blatant disregard for the rights of tourists and trampers".

Ms Leone said her medical condition, called endometriosis, was exacerbated by herbicides, pesticides and dioxins in the environment so she tried her best to avoid exposure.

The couple encountered two other weed spraying incidents in the South Island but say, ironically, they chose to holiday in New Zealand for its clean, green image.

"What happened to us is unacceptable in a country that sells its image overseas as '100 per cent pure and clean'. It's just a joke," said Ms Leone.

"Most times we would see 1080 drops around the tracks and when they spray they don't seem to care if anyone is there. Many of the travellers we met were saying the same thing. New Zealand's 1080 poison and weed spraying programmes will definitely have a big negative impact on your tourism."

Department of Conservation (DOC) biodiversity programme manager Martin Abel admitted his staff were spraying on the day in question but said the closest they would have got to the Heaphy track was 1.5km.

"I can assure you, you were not exposed to any aerial or ground weed spraying," he told the couple.

"Aerial spraying is not done close to the track because we do not wish to expose trampers to any spraying."

- NZPA