Yellow Bristle Grass

Yellow Bristle Grass is a very serious threat to pastures:

Cows don’t willingly eat it
Stock avoidance leads to open pastures in winter/spring resulting in rapid re-infestation
An extremely aggressive annual seeding plant which spreads rapidly through clean pasture
There are currently no selective herbicides for this grass

Yellow bristle grass is difficult to see until it produces a seed head, and by then its seed is probably viable and dropping for next season.

Actions:

Don’t ignore this grass weed
Learn to recognise it now
If only a small patch – isolate and take action to control
Don’t allow it onto your farm in supplement stock food or on contractor machinery etc.

Identification:

Yellow bristle grass is an upright annual growing 25 – 45cm high, although in open pasture its first leaves are typically parallel to the ground. The leaves are yellowgreen to green in colour and usually red or purple at the base. They are flat,
hairless, soft and twisted. The leaf sheath is flattened. There are no ears (auricles) at the junction of the leaf blade and sheath. The ligule consists of a fringe of hairs 0.5 –1.5mm long.

The seed head is a cylindrical ‘spike’, 2.5–10cm long. It consists of many densely packed spikelets, with each spikelet bearing a single seed. At the base of each spikelet are five to ten bristles, 5mm long. Initially the bristles are green, but soon change to a golden-brown. It is the colour of these bristles that give the grass its name. Most other Setaria species have fewer bristles in their seed heads.

Long term management of yellow bristle grass should probably focus on three key areas:

Better pasture competition, which means reducing or eliminating damage to pastures at the time when yellow bristle grass germinates, between October and December.
Elimination of seed production by removing seeds by early topping (before viable seed are set), heavy grazing or chemical spray topping.
For poor pastures complete renovation is the best option, either by going through a summer crop such as chicory (where grass weeds are easily controlled) or by spraying out with glyphosate in early autumn. In either case a strong sward needs to be established before winter. If winter weeds are present they should be sprayed with 2,4-DB or MCPB, which don’t damage clovers, so as not to leave gaps in the new pasture in early summer. Pasture grasses and clovers appropriate to local conditions should be used in the grass mixture.

- Information prepared by AgResearch

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