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Weed of the month: Rock fern / Mulga fern

 Rock Fern/Mulga Fern grows in a variety of situations from open pastures to rocky crevices on hillsides. Although it has not been declared a noxious plant, the fern is poisonous to cattle, horses and sheep if they choose to eat it.

The fern contains nitrates which when eaten by cattle will convert in their rumen microflora to nitrite, then ammonia. Nitrite poisoning affects oxygen transport in the animal and signs include laboured breathing, diarrhoea, inability to stand, disinterest, apparent blindness, episodes of convulsions and signs of nervousness. The animal will have a bloody nasal discharge and blood in their dung and urine. and Sticky Night Some blisters may be seen around their nose and mouth. Death usually follows and will occur quickly if the affected animal is forced to move.  Autopsies reveal internal haemorrhages through all organs.

Stock on my property and nearby properties died between April and September 2014 as a result of eating rock fern. It is not such a problem when there is an abundance of other green feed available but in drought conditions or when good grasses die off, poisoning can occur.

There is no treatment for an affected animal but experiments suggest, though not conclusive, that moving cattle from a fern infested paddock after ten days of grazing to a fern free areafor about three weeks may prevent the build-up of the poison in their system.

In all my forty years in Putty, I have never seen so much rock fern as I have in my paddocks at the moment.  Usually there is a plant here and there but this season it is growing in thick stands.  I have been spraying rock fern withMetsulphuron 600 at the rate of 25 grams/100 litres of rain water or a herbicide containing 300g/L Triclopyr and 100g/L of Picloramat a rate of 500 ml/100 litres of rain water and found both of them effective, the later giving a quicker result.  Both of these products will kill legumes. I have not been able to find any herbicide which is registered as a control for rock fern.

When using any herbicide, read the label on the container and follow the manufacturer’s instructions.

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