Green’s Dictionary of Slang

wattle n.¹

In phrases

up a wattle (adj.) [any of 800 species of the Aus. Acacia; var. up a gumtree]

(Aus.) in error, facing problems.

1914		Sport (Adelaide) : They Say [...] That the mob are up a wattle on Sunday nights. They can’t let a man alone when he’s on a sure thing.
1914		Sport (Adelaide) 17 July 4/2: It seems up a wattle with Willie M. and Minnie M .