The Problem
Ragwort (Senecio jacobaea) is a serious weed problem in Tasmania. It is presently limiting production on about 16,000 hectares of cattle grazed pasture in Tasmania and has the potential to invade 270,000 hectares, which represents a quarter of all cattle grazed land in Tasmania. Ragwort is poisonous to cattle and horses. Each plant may produce 250,000 seeds per year, of which 80% may germinate. Seeds may remain viable in the soil for as lond as 15 years. Once ragwort becomes established it is extremely difficult to eradicate. If the plant is pulled up, it will often regrow from the roots.
The Cost
 Ragwort is thought to cost Tasmania approximately $3 million each year in lost production and control costs. Competition from ragwort causes a significant reduction in pasture production. Once established, ragwort plants are extremely competitive. Second year and older rosettes can make rapid growth and suppress neighbouring pasture plants. When plants die after flowering, bare patches may be left in the pasture, allowing other weeds to establish.
Ragwort now invades approximately 50% (52,500 hectares) of the agricultural land in the Meander Valley Municipality. In 1994 Meander Valley had 114 Dairy Farms milking 19,000 cows and producing 67 million litres of milk. The Department of Primary Industries, Water and Environment estimate that there is a 10% net loss of production due to ragwort. This is costing our Municipality $780,000 or on average $6842 per dairy farm, without considering the cost of herbicide, labour and machinery in control measures. It is estimated that ragwort is costing land managers in the Municipality $2-3 million per year.
Distribution
Ragwort is widely distributed throughout the grazing areas of Tasmania, with exception of the Midlands where it occurs only as isolated plants and small patches. Its spread in this region has apparently been limited by low rainfall and sheep grazing. Infestations also occur on the shores of several lakes on the Central Plateau, and along roadsides in many areas.
The heaviest infestations occur on high inpput dairy pastures in the Meander Valley Municipality. Pastures grazed by cattle are particularly prone to ragwort invasion as the death of desirable plants from cattle hooves leaves openings for seedlings to establish. As cattle normally avoid grazing ragwort it also has a competitive advantage over other pasture plants that are grazed.
Discription
The ragwort seedling has two cotyledons (the first pair of "leaves" to appear at emergence), are 10-15 mm in length and have a characteristic spade shaped blade, notched at the apex. The cotyledons appear at the end of a short leaf stalk called the petiole. After the cotyledons, leaves appear one at a time again on short petioles, the first true leaf being hairless, 10-12 mm in length and oval shaped with a smooth edge (margin). Later leaves are also produced one at a time and the marging begins to show a gradual increase in the degree of lobing and waviness typical of the older ragwort plants. Leaves also continue to become hairer as the plant gets older.
New shoots produced from the growing point or roots after established plants have been damaged are very similar to seedlings, except for the absence of cotyledons.
As the plant matures and forms a rosette (circular cluster) the leaves may vary in length from 50-200 mm. These leaves are stalked, and the blade is deeply lobed and convoluted. Leaf blades are usually deep green on top, and lighter green underneath, often being covered with cottony hairs. The bases of the leaf stalks are often purplish in colour.
At the flowering stage the leaves at the base of the plant die off and the plant consists of an erect leafy stem that branches towards the top. The stems are circular in cross section, ridged, carry long cottony hairs and are often purplish in colour towards the base. Under favourable conditions stems often exceed one metre in height, and in exceptional cases may reach two metres. However, in pasture situations stem height is commonly 500-800 mm. The daisy like flower heads are formed at the end of small branchlets resulting in the production of a dense flat-topped arrangement.
The flower heads vary from 15-25 mm in diameter, and consist of an outer row of 12-13 ray florets ("petals") and 50-60 central disc florets ("tubular petals"). The petals range in colour from almost white to golden-yellow.
Ragwort seeds are small, 1.5-2 mm in length and 0.3-0.5 mm in diameter. The seeds from the petals are smooth, whereas those from the tubular petals or disc region have small bristles which aid in dispersal. Dispersal is also aided by a feathery pappus (parachute) attached to the top of the seed.
Life Cycle
Ragwort if left undisturbed will in the first year form a leafy rosette, and then in the second year flower and die. This is referred to as a "biennial" (two year) life cycle. A biennial life cycle usually occurs in plants growing on waste land or other undisturbed areas.
In response to physical damage ragwort found in pasture normally behaves as a perennial (plants that live form more than 2 years), perhaps flowering several times before dying. This perennial life cycle is promoted by damage to the plant from stock hooves, grazing and cutting.
With the exception of some of the cooler districts the bulk of seed germination begins after the first substantial rain in the autumn, and may continue through to the spring. New leaf shoots from the previous year's plants also appear following autumn rainfall, and may be mistaken for seedlings.
In contrast to the growth of new shoots arising from established plants, the growth of seedlings is normally slow. In pasture, seedlings seldom produce more than five leaves and leaf length seldom exceeds 50 mm in the first year of growth. In open situations rosettes up to 100 mm in diameter may be produced. Seedling mortality is also likely to be high in the first year of growth.
The restriction to growth caused by pasture competition makes seedlings more vulnerable to death from disease, trampling during the winter and drought during summer. Survival rates in the second year are much higher as the rosettes develop.
New shoots are readily produced from the rosette crown (growing point) following damage to established leaves. These may also develop from larger fleshy roots. This capability contributes significantly to ragwort's survival in pasture and commonly occurs following hoeing or pulling when roots become detached from the crown and are left in the soil.
The production of new shoots from the damaged crown can lead to the development of multi-crowned plants. These plants produce a greater number of flowering stems as opposed to that produced from a single crown plant. Continued damage to a plant delays flowering and may lead, over several years, to the development of a very large multi-crown plant.
A very leafy rosette, normally exceeding 150 mm in diameter, develops before stem elongation occurs in the late spring. Several stems may be produced from one rosette. In Tasmania, stem elongation usually begins in early November with flowering commencing in late December or early January. Mature seeds are produced in late January or early February, and seed production may continue until early April. Thus, any control measures aimed at preventing seed production must be completed by early January.
Any action during flowering which damages but does not kill the plant, such as grazing, slashing or incorrect herbicide application is likely to result in the production of new flowering stems. These arise as either branches from the original stem or at the base of the plant. These new stems can continue flowering well into the autumn and even into winter. Plants damaged but not killed at the flowering stage behave as perennials, and commonly continue to produce new leaves after flowering. The majority of seeds are deposited within 20 metres of the parent plant but under favourable conditions seeds may be dispersed by wind for distances of a kilometre or more. Dispersal on the coats of animals, on farm machinery, logging equipment, trucks and other vehicles, and in hay may be more important than wind in long distance dispersal.
Seeds on the soil surface germinate readily following rain in the autumn, whereas seeds covered by soil or litter may exhibit delayed germination. Buried seeds may remain viable for a number of years, possibly 20 years or more.
Preventing seed production is an essential component of any successful ragwort management plan.
Poisoning
Ragwort is also poisonous to all types of livestock. Cattle losses due to ragwort poisoning do occur in Tasmania where stock have been forced to graze ragwort due to food shortages. Further significat losses to livestock production may occur through lowered milk production, or meat or wool losses from ragwort poisoning.
The greatest danger of poisoning to cattle and horses is in hay and silage containing ragwort. Ragwort still retains its poisonous properties when dry, and it is readily consumed in this condition.
Although normally avoided by cattle and horses it may also be consumed when pasture is scarce. Occasionally individual animals develop a 'taste' for ragwort and preferentially graze it. Many herbicides increase the palatability of ragwort and the risk of preferential grazing and poisoning. All herbicides should be considered as having this potential.
Sheep the only stock able to eat ragwort normally graze it quite readily, often showing a preference for it at the early flowering stage. It is because of this that ragwort is less prevalent in pastures grazed by sheep.
The toxicity of ragowrt to grazing animals is due to the presence of a number of alkaloids that cause liver damage. All livestock are affected by these toxic alkaloids although sheep appear to be more tolerant than cattle and horses.
Liver damage in animals exposed to ragwort is cumulative, the amount of damage being dependent upon the quantity of ragwort eaten and the period of time over which it is eaten. However, the onset of clinical symptoms is usually quite sudden, and can occur some time after the stock have been removed from ragwort-infested areas.
Weakness, jaundice and photo-sensitisation are the major symptoms of poisoning. Severe diarrhoea, straining and nervous signs are often seen terminally in cattle, while in horses, lethargy and apparent blindness are common. Sheep poisoned with ragwort accumulate copper in the liver and death is characteristically associated with the passing of red urine ('red water'). This is due to the breakdown of red blood cells caused by the sudden release of copper from the liver. This does not occur in cattle or horses.
There are no satisfactory tests that can be carried out on animals before the onset of clinical symptoms to see if they have suffered liver damage from exposure to ragwort.
Status under the Noxious Weeds Act
Ragwort is declared as a Secondary Weed. Under the provisions of this Act, gazetted weed insectors can require land holders to take any action thought necessary.
In areas where infestations of ragwort are not widespread such as the Midlands, the far North-west, and some areas covered by community weed management strategies, land holders are required to completely eliminate infestations where practicable.
In districts where the weed is firmly established, and its elimination is not feasible, land holders are required to contain infestations and take appropriate actions to minimise spread to neighbouring properties. Land holders carrying out effective control programs will, on request, be afforded boundary protection (100 m clearance) against infestations on adjacent properties.
 
 
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