Cant speak for Aus but in NZ there is a pretty strong top dressing environment. Keep in mind though that the normal route is to start as a loader, ie driving the truck and filling the aircraft. You could be doing that for some time (years?) before being allowed in an aircraft. Maybe Aus is different but you wouldn't turn up to an outfit in NZ and just start flying, irrespective of how many hours you have. In fact your airline time potentially counts against you.
Goes to show there is no pilot shortage in Ag Flying if that sort of stuff still occurs. You spend $50K+ on a license + low level training + crop dusting + whatever other flying experience you have to go and do something any farm worker could do and do it for years just for a 'shot' at crop dusting? Really?
It's like GA in Australia where pilots use to displace every office position from secretary, to bookeeping to IT support because they're cheaper to employ or work for free. Very few other Industries in the world operate like that!