There are several thousand species of Senecio worldwide, of which around fifty are native to Australia. Many introduced senecios have become important agricultural weeds in Australia and others have been cultivated as garden plants.
Senecios contain pyrrolizidine alkaloids and their ingestion poses a potential risk to horses. The plants are usually unpalatable and are unlikely to be consumed in amounts that would cause poisoning.
Horses may eat senecios if other fodder is scarce and the plants may contribute to pyrrolizidine alkaloid poisoning when consumed along with other toxic plants in horse grazing areas. The contamination of hay or other feedstuffs with senecios can pose a risk for poisoning.
Ragwort:
(tansy ragwort, common ragwort, stagger wort, stinking willy, St James wort) Senecio jacobaea [Asteraceae] Ragwort is native to Europe and western Asia. Ragwort is commonly found as a weed in pastures and it can become the dominant species in degraded pastures. It is a declared noxious weed in Victoria, Tasmania, New South Wales, South Australia and Western Australia.
Growth and identification:
Ragwort is a long-lived perennial that grows to 1.2 m. The plant produces numerous seeds that can be spread by wind, water run-off, as contaminants of transported hay and grain or through animal and vehicle movements. The plant can also spread when root and crown segments are broken off and dispersed by cultivation or other practices that move soil.
Young plants form a rosette of leaves. One or more upright stems grow from the centre of the rosette as the plant matures. The ribbed stems are branched towards the top of the plant and they are covered in cottony hairs when young.
The stems are often red or purple towards the base of the plant. The leaves are dark green and hairless on the upper surface and lighter green and hairy underneath. The stem leaves can be up to 15 cm long and most do not have a stalk. The leaves of the rosette can be up to 35 cm long and they are attached to the plant by a stalk that can be 1 3 – cm long. The edges of the leaves are distinctly ‘ruffled’ and convoluted. The plant gives off an unpleasant smell when damaged.
Ragwort usually flowers in summer. The flowers are bright yellow and are arranged in dense clusters at the tops of the branches. The flowers are around 2 cm in width and they have 12 – 15 petals that can be up to 1 cm long. Green bracts that are tipped with black or brown surround the flowers and each flower has many small ‘florets’ in the centre. Small brown seeds are formed as flowering finishes. Some seeds have a ring of fine white hairs at the top and some seeds are hairless.
Fireweed:
(Madagascar ragwort, senecio amarillo) Senecio madagascariensis [Asteraceae]
Fireweed is native to southern Africa and Madagascar. The plant has spread rapidly in Australia, particularly in the past 30 years, and it is a significant problem for farmers. Fireweed is a declared noxious weed in Queensland, New South Wales, the Australian Capital Territory and Western Australia.
Growth and identification
Fireweed is a short-lived annual that grows 10 – 50 cm tall. In good seasons the plant can behave as a short-lived perennial. Fireweed produces numerous seeds and most of these are spread by wind. Seed can also be spread by water run-off, as contaminants of transported hay and grain or through animal and vehicle movements.
The plant can occasionally spread when root and crown segments are broken off and dispersed by cultivation or other practices that move soil. Fireweed can have one main stem or several stems and each stem has many branches towards the top of the plant.
The leaves are alternately arranged along the stem and both the leaves and stem are hairless, or have a sparse covering of hairs. The leaves are 2 – 12 cm long and up to 2.5 cm wide. Their broad base wraps around the stem and the edges of the leaves are usually serrated but can sometimes be smooth.
Flowering can occur 6 10 weeks after – germination in favourable conditions and several generations of the plant can be produced over one season. Flowering usually occurs from late autumn through to early summer but some plants may flower in late summer.
The flowers are yellow and are loosely clustered at the tops of the branches. The flowers are up to 2 cm in width and they have 12 – 15 petals that can be up to 1.4 cm long. Green bracts surround the flowers and each flower has many small ‘florets’ in the centre. As flowering finishes small brown seeds are formed. The seeds are covered in tiny hairs and are topped with a silky tuft of hairs.
Management notes:
- Avoid grazing horses on pastures infested with senecio.
- Check batches of hay and chaff for senecio contamination.
- Individual plants can be pulled out by hand or spot sprayed with herbicide. Remove plants in the early growing stages for best results. Ensure all parts of the plant are removed from the ground.
- The use of herbicides on larger infestations is most effective when the plant is in the small seedling to early flowering stages. Seek advice from local agronomist or weed management agency to select the most appropriate herbicide and spray program for your property.
- Minimise grazing pressure on infested pastures to maintain a good ground cover year-round and prevent fireweed from establishing in bare patches.
- Graze adult non-pregnant goats or sheep on heavily infested paddocks as they are more tolerant to pyrrolizidine alkaloids and will readily eat the weeds. Do not leave these animals on the infested pasture continuously as toxicity problems can occur.
- Improve pastures to increase desirable grasses.
Heliotropes:
Heliotrope poisoning in horses is not commonly seen in Australia. Many heliotrope species are known to contain pyrrolizidine alkaloids and they are potentially toxic to horses. The plants are usually unpalatable and are unlikely to be consumed in amounts that would cause poisoning. Horses may eat heliotropes if other fodder is scarce and the plants may contribute to pyrrolizidine alkaloid poisoning when consumed along with other toxic plants in horse grazing areas. The contamination of hay or other feedstuffs with heliotropes can pose a risk for poisoning.
Blue heliotrope:
(wild verbena, clasping heliotrope, purpletop, turnsole, wild heliotrope, creeping heliotrope) Heliotropium amplexicaule [Boraginaceae] Blue heliotrope is native to South America. The plant is drought tolerant and it can quickly become the dominant pasture species when it rains after a prolonged dry period. Blue heliotrope is a declared a noxious weed in New South Wales and Western Australia.
Growth and identification:
Blue heliotrope is a summer-growing perennial that grows to 30 cm in height. The plant produces a large number of seeds that can be easily spread through water run-off, as contaminants of transported hay and grain or through animal and vehicle movements. The plant can also spread when root and crown segments are broken off and dispersed by cultivation or other practices that move soil.
Blue heliotrope has prostrate (creeping), branched stems that can grow up to 1 m long. The stems are green and are covered in hairs. The leaves are hairy and are a dull green colour on the upper surface and lighter green on the lower surface. They are elongated and can grow to 8 cm long and 2 cm wide. They are alternately arranged along the stems and are attached without stalks. The leaves have prominent veins and are wavy along the edges.
The plant produces a flush of growth from autumn to spring and flowering usually occurs from November through summer into early autumn. In some areas the plant can flower at any time of year. The tube-shaped flowers can be purple, lilac, blue or pink in colour and each has a distinctive yellow throat. The flowers are 4 – to – 6 mm long and are arranged in 2 rows along one side of a curved flower spike.
Common heliotrope:
(potato weed, European heliotrope, Barooga weed, Wanderie curse, bishop’s beard, caterpillar weed) Heliotropium europaeum [Boraginaceae] Common heliotrope is native to Europe, western Asia and northern Africa. Common heliotrope is drought tolerant and once established it can flourish during dry hot summers when other desirable crop and pasture species fail to thrive.
It is a declared noxious weed in Western Australia and Tasmania.
Weed that favours bare, disturbed ground such as fallow areas. Also found in crops, pastures and on roadsides.
Growth and identification:
Common heliotrope is a short-lived annual that grows to 30 cm in height. The plant produces numerous seeds that can be spread by animals, water run-off or as contaminants of hay or grain. The plant has upright or semi-upright branched stems. The leaves are greyish-green and are arranged alternately along the stems. The stems and leaves are covered in coarse hairs. The oval or egg-shaped leaves can grow to 9 cm long and 3 cm wide. The leaves are attached to the stems by stalks that are up to 4 cm long.
The flowers are tube-shaped and are white with a -and are white with a shaped distinctive yellow throat. Each flower is 2 – 3 mm – 3 mm long and the flowers are arranged in 2 rows along one side of a curved flower spike.
Heliotropium ovalifolium:
(Also known as Heliotropium coromandelianum var. ovalifolium or Heliotropium gracile) [Boraginaceae] This native heliotrope grows throughout northern Australia, Asia and Africa. In the late 1990s the plant was implicated as the source of pyrrolizidine alkaloids that caused the death of a number of horses on a property in the Kimberly region of Western Australia.
Growth and identification:
Heliotropium ovalifolium is a perennial that can grow 15 – 80 cm in height. The plant has a branched, semi-upright to spreading growth habit. The smaller branches are covered in curled hairs. The leaves are grey-green in colour and are covered in fine hairs that may be curled. The leaves grow to 7 cm long and 2 cm wide.
The flowers are tube-shaped and are white to pale yellow. Each flower is up to 5 mm long and flowers are arranged along one side of a curved flower spike.
Management notes:
- Avoid grazing horses on pastures infested with heliotropes.
- Check batches of hay and chaff for heliotrope contamination.
- Improve pastures to increase desirable grasses.
- Minimise grazing pressure on infested pastures to maintain a good ground cover year-round and prevent heliotropes establishing in bare patches.
- Graze adult non-pregnant goats or sheep on heavily infested paddocks as they are more tolerant to pyrrolizidine alkaloids and will readily eat the weed. Do not leave these animals on the infested pasture continuously as toxicity problems can occur.
- Individual plants can be pulled out by hand or spot sprayed with herbicide. Remove plants in the early growing stages for best results. Ensure all parts of the plant are removed from the ground.
- The use of herbicides on larger infestations is most effective when the plant is in the small seedling to early flowering stages. Seek advice from a local agronomist or weed management agency to select the most appropriate herbicide and spray program for your property.
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