Australia records first detections of 'devastating' plant disease

A rockmelon root heavily infected with Monosporascus cannonballus. (Supplied: Gerald Holmes, California Polytechnic State University)

The plant pest Monosporascus cannonballus has been detected at two properties in the NT, marking the first cases in Australia.The soil-borne fungus affects the roots of crops such as melons and cucumbers and can rapidly destroy plants if left untreated.

The NT's Department of Agriculture and Fisheries says it will work with industry groups to help growers manage the disease, but it cannot be eradicated.

An exotic plant pest species capable of quickly "devastating" crops has been detected in Australia for the first time.

Monosporascus cannonballus is a soil-borne fungus that causes root rot, according to Northern Territory Chief Plant Health Officer Sally Heaton.

The disease was detected in a cucumber plant in the Darwin region and in honeydew and rock melon crops in the Katherine region, about 300 kilometres south.

Ms Heaton said the fungus had been found overseas in cucurbit plants such as pumpkins, squash, melons, cucumbers and gourds.

"If it's been left unmanaged … what they've seen is whole crops, mature crops, just suddenly die off," she said.

A rockmelon crop that has been severely damaged by the disease. (Supplied: Gerald Holmes, California Polytechnic State University)

Ms Heaton said the NT Department of Agriculture and Fisheries was not sure how the disease arrived in Australia, but it could have been here for a long time.

It was identified in August after two separate farmers noticed something wrong with their crops.

Ms Heaton said the fungus could not be eradicated.

"We were looking at them [the plants] and looking at the fine roots, that's where we detected this fungal pathogen," she said.

The pest has spread in multiple countries including the US, India, Taiwan, Japan and in parts of Europe and the Middle East.

Ms Heaton said the disease caused plants to look as though cannonballs were erupting out of their roots.

Melons Australia chief executive Johnathon Davey said the discovery was concerning and that it was causing "significant loss" for affected NT growers.

"We now need to really work with out growers to understand what the spread of this fungus is and start working with them on how to manage it," he said.

Melons are grown in the NT near Darwin, as well in the Katherine and Mataranka areas. (ABC Rural: Lucie Bell)

Mr Davey said growers were under pressure as they grappled with other challenges, including varroa mite, and that the incursion would likely lead to an increase in production costs.

"Providing fresh melons for Australian consumers is only [going to] become harder," he said.

"This is going to see increased management costs.

"We need to have a discussion about what does it look like for the general community in terms of pricing.

"If it becomes clearer how it got into the country or what that pathway was, we'd expect that there'd be a fairly substantial investigation."

NT authorities are not planning to impose biosecurity restrictions in response to the detections, but Ms Heaton said it was important farmers had their own measures in place.

She said the department would work with industry groups to assist growers, who already took biosecurity seriously.

"They've got good biosecurity practices in place that manage these diseases very well," Ms Heaton said.

"A lot of those practices can be carried over to help deal with this."