Download Hard head thistle fact sheet

Origin
Height
Distinguishing Features
Leaves
Stems
Flowers
Seed
Central Russia, Afghanistan and Mongolia
30 – 90cm (mostly 45 cm)
Erect perennial, 0.4 – 1 m tall, Appears like a spineless thistle. Grey/green plant
covered with fine hairs, leaves larger at the base with lobed edges, smaller at the
top with smooth edged. Small thistle like flowers at the end of branches are purple
to almost white and appear from November to February.
Greyish or silvery grey green leaves with short hairs; rosette leaves up to 15 cm
long, 2 – cm wide; Lower stem leaves without stalks slightly dissected.
Erect stems from the centre of the rosette, stiff branched and with a slightly woolly
covering of soft grey hairs; dark brown to black underground and at the base,
silvery grey to dull grey green above.
Flower heads in solitary clusters on the ends of short, leafy branches. Tubular florets
purple, pink or occasionally white, surrounded by broad thin spineless white or pale
bracts with a thin papery tip.
Seeds whitish or ivory and sometimes mottled, 3 -4 mm long, 2 – 3 mm wide,
wedge shaped often slightly curved with a pappus of numerous stiff, barbed white
hairs, loosely attached. Seeds can remain viable for a number of years under dry
conditions.
Hardheads (Acroptilon repens) also known as Russian Knapweed, hardhead thistle, creeping
knapweed is a weed of irrigated crops and dry land grain
growing areas. It can also invade pastures but is mainly
confined to roadsides, and channel banks in irrigated
pasture areas and is one of the most important weeds of
irrigated vineyards and orchards.
It was first recorded in Australia at Benalla in 1907.
Hardheads are now an important weed in parts of NSW
Photo courtesy of DPI Vic
and North and Northwest Victoria. It is now a major
problem weed in the Murray River Irrigation Area and the Victorian Mallee, and is of major
concern to the Riverina.
Declaration Status – Hardhead is declared under the Noxious Weeds Act 1993 as a Class
4 weed in: Balranald Shire, Berrigan Shire, Central Murray County, Conargo, Deniliquin,
Murray and Wakool Shire.
Class 4, Locally Controlled Weeds, the growth and spread of the plant must be controlled
according to the measures specified in a management plan published by the local control
authority.
Distribution of Infestation
At present there are only 7 existing and 4 eradicated infestations in the Riverina, all being
confined to the southern half of the region bordering with Victoria.
Wakool – 1976 – Private Property – Still existing and also have 4 other isolated roadside
and private property patches in the shire
Balranald – 1991 – Private Property - Controlled no return plants. Two sites have also
been found during roadside spraying of road shoulders in Balranald Shire.
Corowa - 1999 - Private Property and again found on the same property in 2003. It was
found on a small irrigation channel in the middle of a paddock and has spread along the
channel for about 500 metres. The affected farmer is in the process of eradicating it.
Central Murray County Council - have two known infestations. The first near Tocumwal was
discovered in 1994 and treated; constant monitoring has not seen any return plants. The
other infestation on private property is treated and thought eradicated, yet isolated plants
are still being found occasionally.
At present these are the only known infestations of Hardhead Thistle in the Riverina. The
main concern for this region is the level of hardhead thistle infestation in Victoria just over
the Murray River and the general lack of awareness of Hardhead thistle in the Riverina.
Habitat & Description
Hardheads are an extremely vigorous and efficient competitor for water and nutrients. The
extensive root system stores food and makes the plant very hardy. It is an aggressive weed
of cultivation, especially in irrigated and dry land crops and pastures, and can become the
dominant weed when conditions are suitable. It forms dense, smothering patches and
releases allelopathic chemicals that can suppress the growth of other plants. Although it is
grazed freely, this plant may be poisonous to livestock if eaten in large amounts. Prolonged
contact with hardheads may also cause skin sensitisation and dermatitis in humans.
Rosette
photo J.J.Dellow
Seedling
photo J.J.Dellow
Means of Spread
Hardheads reproduce by creeping roots and by seed. Seed is not dispersed to any
significant extent by wind. Seeds may be dispersed by water (particularly along channels),
contaminated farm machinery and in fodder and agricultural seed such as Lucerne.
Grazing animals are also important in dispersal. Seeds can pass through the digestive tract
of livestock in a viable condition and also adhere to their coats.
The main spread is by movement of root fragments by cultivation. Segments as short as 2.5
cm moved by cultivation equipment are capable of establishing new plants wherever they
are deposited.
Control
Effective management of hardheads requires an integrated approach employing a
combination of control measures. The overall aim of the hardheads management should be
to prevent new infestations, reduce current infestation and rehabilitate areas where control
activities have occurred.
Equipment Hygiene is extremely important to avoid spread to properties free of hardheads.
Competitive ground covers such as Lucerne or clover will effectively compete with
hardheads.
Chemical treatment can be a key part of the hardheads integrated management plan but it
is not desirable to have it as the only control action.
Disclaimer: This publication may be of assistance to you but ERNWAG/WRNWAG do not guarantee that the publication is without flaw of any kind or is
wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying
on any information in this publication (2009).