Weed Management in Horticultural Crops

EXERCISE 13

EXERCISE 13: Biology of Parthenium

Seedling	Rosette Stage	Ribbed Stem	Flowers
Juvenile Leaves	Mature Leaf	Fruit	Seed

Seedlings:

Normally germinate in spring and early summer with the onset of rain. A young seedling showing expanded cotyledons and with the first true leaves emerging.

Rosette Stage:

Showing radial arrangement of leave sat ground level.

Mature Plant:

Parthenium weed is an annual herb with a deep tap root and an erect main stem that becomes woody with age. As the plant matures, it produces many branches with flowers and may eventually reach a height of 2 m. Under favorable conditions it can germinate, mature and set seed in 4 weeks.

Flowers:

Are star-shaped with a white to creamy-white appearance. They are produced at the tips of the upper branches. Colour changes to light brown when seeds are mature and about to shed. Flowers have five petals like ray florets, each bearing a single seed.

Ribbed Stem:

Mature stems are longitudinally grooved and covered with fine hairs.

Juvenile Leaves

A newly-emerged pubescent leaf (covered with fine hairs). Young leaves typically show prominent veins.

Ribbed Stem

Mature stems are longitudinally grooved and covered with fine hairs.

Mature Leaf

A mature, pale green and deeply-lobed lower leaf. Mature leaves are branched alternately on the stems and are less hairy than young leaves.

Fruit and Seeds

Seeds are flattened achenes, dark brown to black in colour with white appendages. The seeds are protected in a straw-coloured fruit covering. A single plant can produce up to 28,000 seeds which are spread by vehicles, machinery, animals, pasture and crop seed lots, stock feed, wind and water.