• Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Annual, upright growing grass 25-45cm high
  • In open pasture its first leaves often grow parallel to the ground
  • Leaves are hairless, twisted and slightly rough at the edges, and yellow-green to green in colour
  • Leaf sheath is flattened and hairless and often turns reddish purple
  • Ligule is a ring of hairs about 1 mm long
  • No ‘ears’ (auricles) at the junction of the leaf blade and sheath
  • Seed head is a cylindrical ‘spike’, 2.5 – 10 cm long, with many densely packed spikelets. Each spikelet is surrounded by five to ten bristles, 5-8 mm long which are green initially but later turn golden-brown
  • Most of other species of Setaria have fewer bristles in their seed heads.

  • Germination typically starts in mid-October and peaks in mid-November depending on weather. Germination can begin at 16°C but optimal temperatures are between 20 and 30°C
  • Early seed heads appear in late December but mostly in January and February
  • Mature plants and empty seed heads will persist until the first frost. YBG reproduces only by seed
  • Seeds are dispersed by water (seeds are hard-coated and most float on water), soil movement, animals, and as contaminants of hay and maize. The barbed seeds stick to and are often carried in fur, feathers, or clothing
  • Seeds are usually dormant at maturity and require about 3 months of after-ripening before they can germinate
  • Most seeds survive only a few years under field conditions although, some deeply buried seed may survive for up to 10 years
  • Seedlings can emerge from soil depths up to 10 cm but optimal germination is from 1 – 2 cm depth
  • Counts have shown seed numbers in the soil up to 20,000/m2 but typically 5 – 10,000/m2 under light infestations.

Origin

  • There are eight species of Setaria in New Zealand, most of which are annuals. Overseas they are commonly called foxtails or millets
  • Yellow bristle grass (YBG) originally came from southern Asia where it is…“A relatively good natural grazing species, although leaf production is moderately low. It is a serious weed in some areas, especially since it only germinates late in the season once most control measures have already been applied. In some areas this grass plays an important role in stabilising bare soil to protect it from erosion” (- see references under ‘Further Information’)
  • YBG has now spread throughout Europe, Africa, North America and Australia
  • Although common on roadsides, YBG has ‘jumped the fence’ in the last 10 years and become a big problem in many farming regions throughout New Zealand.

Life-cycle

  • YBG occurs in areas with adequate summer rainfall, usually over 500 mm per year, although it can tolerate dry conditions once established
  • Grows in areas where the soil has been disturbed and especially where water collects, including cultivated areas, old pastures, along footpaths and the side of roads
  • Has a C4 photosynthetic pathway meaning that it grows best at higher temperatures and is frost tender
  • Fills a similar environmental niche as other C4 summer annual grasses such as crowfoot grass, summer grass and smooth witchgrass
  • However, due to the size and number of the seed produced it is more competitive than other species
  • Moderate to slow-growing, especially if the weather remains cool, and generally will not establish and compete in vigorous ryegrass/white clover swards
  • Not toxic to stock but they may avoid grazing the seed head. When grazed, YBG seed survives passage through the rumen and can be found in dung, where it establishes in any gaps
  • Readily invades run-out or damaged pastures that have been opened up by pugging, over-grazing or the death of flat weeds or winter annuals such as annual poa.

  • Yellow bristle grass (YBG) does not provide good feed in late summer/autumn resulting in lower pasture quality. This can reduce milk production from YBG infested dairy pastures
  • Selective grazing can lead to lower pasture utilisation
  • YBG competition weakens ryegrass plants
  • YBG death opens pastures for establishment of winter weeds.

Chemical control

  • Fenoxaprop (Puma S) is the first selective herbicide to be registered for the control of yellow bristle grass (YBG) in pastures
  • Fenoxaprop ) has a withholding period of 28 days, during which pastures must not be grazed
  • Fenoxaprop should be applied 7 days after grazing to ensure that there is sufficient YBG regrowth for the herbicide to be effective
  • Most effective on young seedlings – it will not kill YBG seeds once seed heads have matured.

Management on roadsides

  • Spray with glyphosate or fenoxaprop – timing is important, ideally spray before the 1st seed head emerges (late December to January depending on season and weather)
  • Try and create a thatch of dead plants to stop further YBG germination
  • Residual herbicides can prevent germination of YBG
  • Mowing won’t kill YBG but seed will be produced very low down and is therefore less likely to spread
  • Manual removal is an option for small amounts
  • Roadsides containing YBG should NOT be grazed between December and May
  • Don’t make infested grass into hay because the seeds can survive. Wrapped balage is suitable, provided it’s left for at least three months.

Management of small infestations

  • Use glyphosate or fenoxaprop to spray out the infestation but note that other weeds will quickly fill the empty space
  • Glyphosate can be used at all stages of growth but glyphosate or fenoxaprop will not kill the YBG seed if the bristles have already turned yellow. Fenoxaprop is best applied when the plants are at seedling stage
  • Manual removal of plants before seeding is a very good option if it is possible
  • Areas with YBG can be fenced off to stop seed being spread further afield
  • Don’t graze when the seed head is visible – this is too late – seeds can spread and germinate in dung
  • Be vigilant as YBG will germinate throughout the summer as conditions (rainfall) allow.

Management of large infestations

  • If using herbicide, note that more than one application may be required – most YBG germinates in late spring / early summer but some YBG will germinate much later in the season
  • Topping will improve utilisation and possibly reduce the quantity of YBG seed set
  • Avoid grazing a clean paddock after stock have been exposed to YBG seed
  • Use chain harrows to spread dung and avoid creating conditions which favour YBG establishment.

Management by pasture renewal

  • There must be two summers out of YBG seed production before new pasture is sown and during that time YBG must not be allowed to set seed!
  • Use crops in which YBG can be readily controlled e.g.
  • maize (use Latro as a post-emergence spray)
  • chicory (use Sequence as required)
  • turnips (use Sequence prior to crop canopy closure)
  • lucerne or other legume (use Sequence as required)
  • for annual summer crops plant annual ryegrass or winter cereal in between.
  • Look after new grass and keep all weeds out
  • Otherwise use normal pasture renewal principles (e.g. treated seed and appropriate endophyte, etc.) refer to Dairy NZ’s Pasture Renewal Guide.

Grazing management

  • Avoid overgrazing and opening of pastures to weeds
  • Overgrazing in summer can also expose the ryegrass crown to direct radiation and may kill the plants
  • Avoid moving stock from an infested to a clean paddock
  • In dry years supplementary feed might be needed early to prevent overgrazing
  • YBG will not be controlled by grazing as mature seed heads are produced within 21 days of grazing
  • Reduction of stocking rate may be required to achieve some of the above.