Mature feathertop stands out as a silvery sheen in the pasture, especially when seen silhouetted against the sun</</p>
The wire grasses (Aristida spp.)
Wire grasses grow in various soils throughout the tropics and warm temperate regions of the world. In Australia they grow mainly in sandy soils, although feathertop is dominant on clays. There are 56 individual species of wire grass in Australia, with about 330 found throughout the world.
Feathertop (Aristida latifolia)
Feathertop degrades the value of pastures and reduces wool quality. It is a native perennial tussock grass that can be prevalent following summers of above average rainfall but generally declines during droughts. It is relatively unpalatable with low nutritive value (crude protein is 3.1 to 6.2%) and sparse leaf production.
The seed heads are borne on stalks up to 100cm tall and are 25 to 40cm long, branched and distinctly drooping. Mature feathertop stands out as a silvery sheen in the pasture, especially when seen silhouetted against the sun.
Seeds are dart-like, 35 to 40mm in length, with sharply pointed tips and backward pointing hairs followed by obtusely fanned awns. The awns generally account for at least half of the total length of the seed. The shaft of the seed is twisted like a corkscrew. This allows the seed to easily penetrate the staples of wool, but prevents it from being combed out.
Feathertop wire grass seedlings are up to 15cm in height (depending on age)
Recognising feathertop seedlings
Feathertop seedlings are distinct from others in the Mitchell grasslands. Up to 15cm in height (depending on age), with long thin leaves and a thin stem, there is always a tuft of wispy white hairs at the base of the leaves.
Seedlings can grow quickly, producing new seed heads within six to eight weeks under wetter conditions.
Recognising feathertop seedlings can be a good way to identify future problems - densities of 25 seedlings per m2 signify a potential problem over the current, or following, summer.
Map 1: Feathertop is found in northern Australia, especially in Mitchell grass country
Feathertop grows predominantly in the clay soils of the Mitchell (Astrebla spp.) grasslands and is one of the most widely distributed wiregrasses of northern Australia.
Survey results indicate it was present on 85% of western Queensland properties between 1988 and 1993 and that 57% of those properties lost money as a result.
Soil factors, rainfall and grazing may all influence where, and how much, feathertop grows. Scientific publications report that levels of feathertop increase in good summer seasons. Continuous light grazing leads to slow increases in feathertop plant numbers, whilst a single period of overgrazing can favour increases in the size of seedlings.
Figure 1: Feathertop seed fall was monitored from October 1993 to May 1997. Generally, seed falls from plants for six to eight weeks during March to April
Avoiding seed contamination
Feathertop seed is a major irritant and can lead to wool discolouration and cotting, as well as ill-thrift and reduced wool production, especially in young sheep. Sheep may die if ill-thrift is associated with adverse weather events such as heatwaves. Shearing is the only known way to relieve the pain and discomfort that sheep suffer from high levels of seed in the skin and carcass.
Vegetable matter (VM) in fleeces can be 3% or higher as feathertop infestations increase. Discounts currently range from 2 to 115c/kg in medium wools with 2 to 6% VM (AWEX Wooltrak, Northern Region Premium and Discount Report 31/10/02). Heavier skirting of fleece wool is often required to minimise VM.
The National Livestock Reporting Service's (provided by Meat and Livestock Australia) National Weekly Skin Report (25/10/02) shows that VM in sheepskins also presents a major problem. The average discounts for lambskins, Merino sheepskins and crossbred sheepskins from carcasses in the medium weight range were $3.21, $2.29 and $1.86 per skin respectively.
When should I consider an avoidance strategy?
Avoidance of feathertop seed is a viable strategy provided:
- more than 25% of the plants in a paddock are feathertop (see Feathertop wire grass: rating infestations for more detailed information)
- rainfall conditions suit an avoidance strategy
- you are able to de-stock the infested pasture for six to eight weeks at little cost.
Conditions for avoidance
Feathertop produces most of its seed over a period of six to eight weeks. This, in turn, occurs six to eight weeks after receiving 50 mm or more of rain, especially between October and March. Greatest seed production is generally from March to April, but can extend for longer periods under wet conditions.
The pattern of seed fall creates an opportunity to remove sheep for six to eight weeks from paddocks heavily infested with feathertop to avoid wool, skin and carcass contamination.
However, if you are experiencing a wet summer and these good rains continue, feathertop may produce considerable amounts of seed for longer periods. This makes it difficult to avoid contamination. Under these circumstances, control methods may be more appropriate.
Checking your worst feathertop paddocks can help you decide when to move stock, and to where. Once the majority of feathertop seed changes from green in colour and starts fanning its three awns to produce a dart-like seed head it is time to move.
Moving stock to avoid feathertop seed problems depends on the availability of alternative paddocks with less feathertop and enough pasture to feed the additional sheep for six to eight weeks.
The paddocks you have removed sheep from to avoid feathertop can be spelled or stocked with cattle. If additional paddocks are not available, agistment is usually only an option where it can be purchased for less than 8c/sheep/week.
Moving sheep to paddocks with lower feathertop levels may not suit your own management, and will not help control the problem. In many circumstances, however, it can be an effective strategy to reduce contamination from feathertop seed.
- Contact the Customer Service Centre
Related feathertop wire grass management information:
Related Mitchell grass management information: