YELLOW BRISTLE GRASS

Setaria pumila 

DESCRIPTION

Yellow bristle grass (YBG) is a tufted annual grass that is characterised by its bristly seed head which is not liked by stock and is becoming a major problem in pasture in some parts of the country.

Originally from sub-tropical China YBG is now widespread in Europe, Africa USA, and Eastern Australia and is now commonly found along the side of many North Island roads. It is becoming a significant problem in these areas as it moves from the roadside into pasture.

YBG is usually an upright annual growing around 25-45cm tall although in open pasture it can be more sprawling with first leave parallel to the ground. Red or purple at the base the leaves are normally green or yellow-green in colour with a flattened leaf sheaf.  

The seed head is a 2.5-10cm cylinder comprising of densely packed spikes with each small spikelet containing a single seed. From the base of each of these spikelets, you will see 5-10 hairs or bristles around 5-8mm long.  Initially, the bristles are green but these rapidly change to yellow giving YBG its characteristic name.

Typically germination starts mid-October and peaks mid-November – mid-December. Early seed heads can appear in late December but are usually found in January and February. A single plant can have 60-90 seed heads and the seeds, which are heavier than summer grass seeds require up to 3 months after ripening before they germinate. Normally lasting only a year or two under normal conditions deeply buried seeds can be viable for up to 10 years.

CONTROL MEASURES TO REDUCE THE SPREAD OF YBG

• If roadside contractors are mowing then leave a tall grass line between the roadside and the fence to help minimise the spread of YBG.
• Check incoming hay and if spotted feed this out in an area where a non-selective spray such as glyphosate can be used to kill any seedling growth.
• Make silage rather than hay if YBG is present.

HERBICIDES TO CONTROL YELLOW BRISTLE GRASS

Spray Herbicides to Kill Yellow Bristle Grass (YBG)

Non-selectively

• G-360 GLYPHOSATE – 6-9L/ha by boom spray, 1L/100L by handgun or 150ml/15 L in a knapsack sprayer.
• G-540 – GLYPHOSATE – 4-6l?ha by boom spray, 660ml/100L by handgun and 100ml/15L in a knapsack sprayer.
• Granny Herbicide – 2.7-3.8L/ha by boom spray, 450g/100L.
• Halox 100 EC – 600ml/Ha by boom spray, 600ml/100L by handgun or, 20ml/15L knapsack sprayer. This is quite cost-effective if spraying out pasture grass containing YBG but it won’t kill weeds in the pasture as glyphosate will.

As these are non-selective they will kill all other pasture grasses as well.

Selective Herbicides to Kill Yellow Bristle Grass

Traditionally only fenoxyprop active ingredient has been approved to selectively kill YBG in pasture. This is known by the brand names of Puma S and Panther amongst others. This active ingredient has traditionally been very expensive.

There had been a lot of anecdotal evidence that asulam active ingredient was successful also. This is known under the tradename Asulox and Dockstar but Nufarm did trials and had this added to their Dockstar label so Dockstar is the only official ‘on-label’ asulam-based herbicide registered to kill YBG. Asulam though is a much cheaper alternative to fenoxyprop-based herbicides.