Tuesday, September 13, 2016

The Curse of the Tussock

We have four main weed problems around here. They are bracken, tussock, scotch thistle and blackberry.
We have overcome the bracken problem with the use of metsulfuron-methyl (BrushOff or Associate) which appears to have a long lasting affect. The other three need to be treated annually. We have the latter two well under control but the tussock is prolific, hardy and reproduces easily from seed.
There are two main problem tussocks in Australia. One is serrated tussock (Nassella trichotoma) an import from South America. It is the worst perennial grass weed in Australia which can reduce pasture production by up to 95%.
It was introduced into Australia in the early 1900s, probably as a contaminant in hay imported from Argentina, and was first identified as a weed in 1935.
Poa tussock: Living, Dying, Dead

The other is the native poa tussock (Poa labillardierei).
Thankfully we have the native variety which is easily treated by spot spraying with glyphosate (Roundup).
This can be a tedious task but on a warm spring day wandering the paddocks with a backpack sprayer can be good therapy.
The old saying 'one year's seeds equals seven year's weeds' is particularly true with this plant.
The main problem is it reduces pasture productivity and has little nutrition for stock.
It takes some time for the chemical to work. The mode of action is to interfere with the plant's metabolism eventually starving it to death.
Two to three weeks after spraying a yellowing of leaves is noticed then a gradual senescence.
No matter how many we kill off each year there is always a new crop the following one.
True the overall number is decreasing but there are still thousands so guess this will be an annual job for years to come.
What we like to see
Our glysophate 450 addition rate is 10mL/L. We use a cheaper generic product rather than Roundup.
In cases where we need to improve the rain fastness of the mix (from 6 to less than 1 hour) we add an organo-silicone surfactant at a rate of 2mL/L.
This penetrant increases the surface area of the droplet, increases the rate of uptake and, on hard-to-wet weeds, increases the amount of herbicide entering the plant.

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