Pond apple survey work

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.