False yellowhead is a prolific seed producer and a threat in the higher rainfall regions of southern Australia. It is known to release substances that inhibit the germination of nearby plants, and to be toxic to stock. The oil on the leaves and stems causes contact dermatitis, resulting in itching and blistering skin. Stock that eat the flower heads of D. graveolens (stinkwort), a similar species, can develop enteritis (inflammation of the small intestine) because the pappus irritates and punctures the lining of the small intestine, eventually leading to pulpy kidney disease and sudden death if untreated. It is thought that false yellowhead would have similar impacts on grazing animals.
False yellowhead is native to southern Europe (including France, Spain, Greece, Italy and Bulgaria) through to Turkey and the Middle East (Israel, Jordan and Syria). It is also found in northern Africa (Algeria, Egypt and Libya). It is not clear how false yellowhead was introduced to Australia but it may have escaped from a garden. It was first recorded in Albany in 1955, and has since spread throughout southern Western Australia.
False yellowhead is well established on the south coast of Western Australia, having spread from Albany to Mount Barker and Denmark, some 40 km to the west and north respectively. There are established remote populations at Walpole-Peaceful Bay, 60–80 km west of Albany, and at Mount Manypeaks, 60 km east of Albany. An isolated population has also been recorded on a train track at Yarloop some 350 km northwest of Albany and 125 km south of Perth. This infestation was probably spread by seed attached to a train.
False yellowhead spreads by seed. Seed dispersal is aided by the ‘pappus’, an arrangement of bristles at the end of the seed, which catches the wind or can assist flotation. Seed can also be spread during soil movement (eg in road making or road grading) or when attached to machinery.
False yellowhead is an erect, perennial, soft-wooded shrub, 1–1.5 m tall and 1 m wide.
Its leaves are greyish-green and elliptical (ie oval-shaped with the ends pinched together), 25–100 mm long and 8–30 mm wide, and serrated on the edge. There is no stalk and the leaf base is half-wrapped around the stem (partially stem clasping).
The yellow flowers are daisy-like and 10–20 mm across, with radiating petal-like florets. The flowers are surrounded by narrow, triangular, sticky bracts (modified leaves) 3–9 mm long.
The seeds are approximately 2 mm long, with about 15–25 bristles at the base.
The roots can be quite substantial, even in small plants.
The young stems and leaves are covered with glandular hairs which exude a sticky foul-smelling oil. The oil can cause allergic reactions.
False yellowhead usually prefers, but is not restricted to, high rainfall areas. It can be found on both clay and sandy soils. In southwestern Western Australia it is found in areas of medium to high rainfall (ie where rainfall exceeds 400 mm per year). It is more reliant on moisture than the closely related stinkwort D. graveolens, which is a weed of grazing land and roadsides of much of southern Australia.
In southwestern Western Australia nearly all records of false yellowhead are from highly disturbed sites: road verges (20 records), firebreaks (one record) and walking trails (two records). Of the three records from bushland, all are from disturbed sites in swamps (Lake Seppings, Mount Manypeaks, and a creekline and swamp at Emu Point).
CRC for Australian Weed Management: Greg Keighery (WA CALM), John Moore (WA Agriculture/Weeds CRC), Ryan Munroe (City of Albany), Karin Baker (Friends of Mt Adelaide and Mt Clarence) and John Thorp (National Weeds Management Facilitator).
Because there are relatively few false yellowhead infestations, and it can potentially be eradicated before it becomes established, any new outbreaks should be reported immediately to your local council weed officer. Do not try to control false yellowhead without their expert assistance. Control effort that is poorly performed or not followed up can actually help spread the weed and worsen the problem.
Suitable control methods would include; spraying, manual weeding with appropriate tools and protective clothing. Follow-up control programs are essential.
False yellowhead (Dittrichia viscosa) is not declared in NSW under the Noxious Weeds Act 1993.