Thursday, 1 March 2018

Spot spraying weeds prolongs pasture production


Spending a little time over summer to tidy up scattered weeds in pastures by spot spraying can pay dividends. The old saying ‘one year’s seeding makes seven years weeding’ rings true.

It is important to ensure those scattered weeds do not get the chance to set seed and fill the seed bank if you don’t want to be forever playing a game of Whac-A-Mole. Weed seeds will survive in the soil for a long time, setting itself up to take advantage of opportunities in the future to germinate and establish a new population of weeds. This reduces the production and quality of pastures and shortens their productive life by effectively strangling the pastures ability to absorb nutrients, water and sun.

The equivalent to the Whac-A-Mole mallet to get rid of those pesky weeds is a grass-friendly herbicide for spot spraying weeds such as clopyralid (Multiple).


If you’re targeting thistles, such as nodding, scotch, variegated or winged, a dilution rate of 25ml of Multiple to 10L of water for knapsacks or quad-bike/ATV sprayers is very cost effective, compared to grubbing and other chemical options. Whilst it will kill clovers, the clovers are only effected in the spot where the thistle was, and clopyralid (Multiple) residues do not last in the soil so it will not be too long before clovers can recolonise the spot. Clopyralid is also very good for weed wiping Californian thistles. Research at Massey University has shown a single pass at 500ml/10L in the weed wiper can be just as effective as a double pass at the label rate of 250ml/10L.

Broadleaf and brush weeds

If there is a range of broadleaf weeds such as docks, ragwort, thistles or even brushweeds like blackberry, broom and gorse, then a combination of the herbicides triclopyr and picloram (Eliminate Bruskiller) is a good option. This grass friendly herbicide will control a range of weeds.

For normal broadleaf weeds no additional surfactant/wetting agent is required, but if you are targeting brush weeds then results will improve with the addition of a quality organosilicone penetrant such as Accelerate. This reduces the rainfast period and improves plant uptake.

If you’re on a budget, metsulfuron (Eradicate) is a very low cost option and also controls a very wide range of broadleaf and brush weeds. However, it will damage most pasture species, so great care must be taken if metsulfuron is going to be used. 

Tip - Adding a neutral spray marker dye (Assist Easy Red) will improve the efficiency of application, making it quicker and easier to avoid missing those pesky weeds or doubling up.