Mimosa pigra is a weed of national significance that covers more than 100,000ha of the Daly, Finnis, Adelaide and Mary River catchments of the Top End. Control of mimosa was the focus of a recent field day held by RM Williams Agricultural Holdings on Labelle Station.
One of the most discussed topics at the field day was whether to windrow and burn dead mimosa stick. Burning an area is usually only done once, and then left to allow grasses to establish and provide competition.
There were arguments for and against burning, and the final decision will most likely depend of the type of country and level of infestation.
· Destroy mimosa seed and deplete the seedbank (but mortality may only occur in the top few centimetres of soil)
· Promote seed germination to be killed in follow-up control, or drowned in floods (to be successfully drowned the country will require quick and deep flooding to ensure seedlings don’t outgrow rising waters)
· Open access for aerial spraying. Thick areas of dead stick can shield seedlings and change droplet size from small to large. This can reduce kill rate and may increase risk of resistance.
· Access for ground control
· Reduce impact of sticks washing away with floods and destroying fences.
· Fire may kill grass seed and leave scarring, particularly if the grass is couch and the fire is slow and intense (GS). This risk is lessened if seed from grasses, should they occur nearby, are likely to be washed into the area. Alternatively, you could plant grasses on the upstream side of the controlled area and let water move the grass into the area.
· Sticks can be helpful to hold up some of the flood debris and any grass seeds within.
· Leaving dead stick provides a flag for pilots doing aerial spraying.
· Burning can promote Melaleuca (paperbark) invasion.
· Late dry season fire might get away and burn the rest of the station.
RM Williams Agricultural Holdings are considering trialling fire over the next few years.