Parthenium hysterophorus

Parthenium hysterophorus is a species of flowering plant in the aster family, Asteraceae.   Originated from the American tropics, it is now spread all over the world.  It invades all disturbed land, including farms & plantation, pastures, roadsides, park and gardens in India, Australia, Africa and Asia.

Biology

P. hysterophorus is an annual plant of the Asteraceae family. It normally grows to 30-90 cm in height, but can grow up to 1.5-2.5 m.   It occurs in humid and subhumid tropics, capable to grow on a wide variety of soil types

Flower heads are both terminal and axillary, penduculate and slightly hairy; composed of many florets formed into small white capitula, 3-5 mm in diameter.  Each head consists of 5 -8 fertile ray florets and about 40 male florets.  First capitulum forms in the terminal leaf axil, with subsequent capitula occurring progressively down to stem on lateral branches arising from the axils of the lower leaves.  Thousands of inflorescences may be produced at the apex of the plant during the season.

  

Seeds are black, flattened, about 2 mm long.  A plant can produce about 15,000-25,000 seeds.  Seeds buried in soil can remain viable for at least 4-6 years.  Germination occurred at 10-25°C, over wide range of soil pH.  Germination rate is extremely high.

 

Flowering may begin as early as 4 weeks after germination.  Life circle is about 86 days under optimum conditions, up to 335 days under unfavourable conditions.

Physiological studies have shown that P. hysterophorus has a low photorespiratory activity and has the C3 photosynthetic pathway but with positive C4 tendencies.

Its wide adaptability, photo- and thermo-insensitivity, drought tolerance, strong competition, allelopathy, high seed production, longevity of seeds in soil, small and light seeds that are capable of long distance travel via wind, water, birds, vehicles, machinery, contribute to its rapid introduction worldwide.

Noxious Weed

Parthenium hysterophorus is a vigorous weed that colonises pastures and farms.  Its presence reduce the pasture and crop production, as well as threatening the local biodiversity.

The presence of P. hysterophorus pollen grains inhibits fruit set in tomato, brinjal, bean, etc.

It found its way to India in the 1950s via contaminated wheat imported from the USA.  Today, approximately 2million hectares of land in India have been infested with P. hysterophorus.

P. hysterophorus was introduced to Australia via the movement of military aircraft and machinery during WW2 and pasture seeds.   In Queensland, it is declared a Class 2 plant under the Land Protection (Pest and Stock Route Management) Act 2002.

Health Hazard

P. hysterophorus is linked with several health problems, both in human and domesticated animals.

Contact with P. hysterophorus causes dermatitis and allergic respiratory problems in humans and cattle, due to the presence of toxin parthenin. 

Livestock fed on grass mixed with its leaves too will develop deteriorated quality of milk and meat.

It also causes diarrhoea, severe popular erythematous eruptions, breathlessness and choking.

Benefit

P. hysterophorus is used in its native neotropics as herbal remedy for various intestinal and skin disorders.  It has potential medicinal properties for skin inflammation, rheumatic pain, diarrhoea, urinary tract infections, dysentery, malaria and neuralgia.

Compost produce from P. hysterophorus can lower weed population, possibly due to allelophatic compounds present in it.  The allelophatic substances may be used as insecticide, herbicide, fungicide and nematicide.

Removal of heavy metal and dye from the environment.

Control

Chemical control with glyphosate has found to be unsuccessful.  Paraquat is effective only when the plant is young.  Manual removal can only be done when the population is small.

 

Biological control by leaf-feeding beetle from Mexico, Zygograma bicolorata is reported to be able to defoliate and kill the plant.