Aerial surveys in the Tully and Murray Upper region have helped to understand the extent of pond apple, a Weed of National Significance, at the top end of these catchments.

The Murray River catchment is the most southerly part of the region with major outbreaks of pond apple so the goal is to keep it from spreading further south to Cardwell, the Ingham district and beyond.

Terrain NRM’s Deb Bass said drones and a helicopter were used to search for pond apple after mapping wetland areas and selecting more than 25 survey sites.

“It is known there is pond apple in the Tully and Murray floodplain – we wanted to find out the extent of the problem further upstream,’’ she said.

Two-year life cycle for pond apple seeds

“Pond apple seeds have a two-year life cycle so if control work can continue for two to three years it is much more achievable to contain an outbreak.

“Isolated pond apple trees have been found further south in the Lower Herbert, but ongoing weed control by the Hinchinbrook Shire Council has prevented it from spreading. It has also been found in the Mackay region and some of the Torres Strait Islands. If pond apple is caught early, by removing mature trees from upper catchments and continuing to monitor for seedlings, there is a good chance of removing the seed bed.”

Recent aerial surveys identified more than 15 pond apple sites in wetland areas in the upper Tully and Murray catchments. The plant, which is listed as a Weed of National Significance, grows into thickets and can take over areas, especially swampy spots, impacting fish species and replacing whole ecosystems.

2000 hectares covered by pond apple in the Wet Tropics

Pond apple currently covers 2000 hectares in the Wet Tropics region. Its seeds and fruit spread via water, especially in floods, and via feral pigs. Terrain NRM removed more than 20,000 mature pond apple trees in the Upper Warrami and Corduroy Creek wetland areas of the Murray River catchment in recent years and followed up last year with seedling removals from the same sites.

Treatment methods include mechanical control, herbicide control and fire, with a combination of those methods often used.

Ms Bass said the survey results, which would be shared with relevant organisations, could be used to source funding and plan future whole-of-catchment weed control work.

The search is on for pond apple in the Murray Upper region south of Tully, where aerial surveys will begin in coming weeks.

Terrain NRM’s Deb Bass says drones will be used along waterways and wetlands in the Tully-Murray flood plain area to discover the extent of pond apple and other invasive weeds.

Pond apple is a major environmental weed in the Wet Tropics region and the Murray River catchment is the most southerly part of the region with major outbreaks. It grows in thickets and can replace whole ecosystems.

“We want to prevent its spread,’’ Deb said. “The seeds stay viable for two years. But by removing mature trees from the upper catchment, and continuing monitoring for seedlings, we have a good chance of removing the seed bed.

“Isolated pond apple trees have been found further south in the Lower Herbert but ongoing weed control by the Hinchinbrook Shire Council has prevented any spreading.”

Terrain NRM is working with the Department of Agriculture and Fisheries on a pilot study, and with landholders, Canegrowers Tully, Sugar Research Australia, Cassowary Coast Regional Council, Biosecurity Queensland, the Department of Resources and the Queensland Parks and Wildlife Service.

Deb said drones surveying would only be over wetlands.

“The last catchment-wide survey for pond apple was in 2008. Pond apple now covers 2000 hectares in the Wet Tropics region and it’s spreading in floods when seed and fruit travel downstream. The seeds are also spread via feral pigs.”

The upcoming survey work follows on from pond apple control work as part of Terrain NRM’s ‘Fish Homes and Highways’ project. More than 20,000 mature pond apple trees in the Upper Warrami and Corduroy Creek wetland areas were removed in 2021 and 2022 and there was follow-up work last year to remove seedlings at the same sites. In the process, larger patches of pond apple were found in wetlands.

Deb said survey results would be used to source funding and plan future whole-of-catchment weed control work. The focus area is from the Bruce Highway west to the foothills of the Upper Murray River catchment.