The Animal Health Board (AHB) is planning a 1080 possum control operation over about 37,000ha of land in the Catlins this winter.
While the AHB's aim was to reduce possums, the vector for Tb, with 1080 drops, Doc used them to control rats and stoats which were predators of mohua. Both organisations had gained efficiencies and reduced costs by working together in the past.
Doc biodiversity programme manager Dave Agnew said while possum numbers had reached the threshold of needing control for the AHB, they were still below that threshold on the 10,000ha of Doc land home to mohua.
Beech forest monitoring had shown the seed fall from last year's flowering, which provided food for the pests as well as the mohua, was at 400 per sq m.
In a full beech mast 5000 to 10,000 seeds fell per sq m and as a result mice, rat and stoat numbers increased dramatically and had been known to nearly wipe out mohua during their vulnerable breeding period, Mr Agnew said.
An indicator of a heavy seed fall was a hot summer, which South Otago had experienced this year, so this time next year, pest numbers could skyrocket.
The dilemma was whether or not Doc should ''piggyback'' on the AHB's operation this year or wait to do its own operation next year when it was predicted a full mast could occur, he said. However, it was not known how many of the trees which flowered last year would flower again this year.
''Ours is a lot trickier to predict.''
Recent monitoring of mohua had shown a healthy population but pest numbers were starting to increase.
However, pests would be affected, as the AHB's drop outside Doc's boundary reduced pest numbers.
Once the latest round of pest and seed monitoring was analysed by Doc's scientists, a decision would be made. Doc was working closely with the board in the meantime, Mr Agnew said.
AHB Southern South Island programme manager Brent Rohloff said the 1080 drop was in response to the natural increase in possum numbers in the area since its last drop in 2008.
This time the AHB would be reducing the bait's toxicity from 2kg to 1kg in response to the latest research showing a lower level could be successfully used for control.
