Potato weed a common garden pest
Galinsoga parviflora or Tridax parviflora .
Its common known names include Potato weed, gallant-soldiers, small flowered galinsoga
Potato weed is native to Central America, but has been introduced through much of the world.
Galinsoga parviflora or Tridax parviflora was brought from Peru (south America) to Kew Gardens in England in 1796, and later escaped to the country and gardens in Great Britain and Ireland. It got its common name potato weed because it being commonly found as a weed in potato crops in Ireland and England. The seeds were transported on trade ships among cargo to many parts of the British Empire, including Australia where the seeds spread into gardens and pastures of the colony. Since then it has continued to spread along the coast by wind, in river systems floating in water, in cattle fodder, animal waste, on vehicles, and on human clothing. It is now widespread south to Victoria, north along the coast to Queensland and the Northern Territory, and west to locations around Perth in Western Australia.
Potato weed is a tough resistant plant that will grow in sandy, loamy and clay soils. It flourishes in moist soil conditions near natural water systems, irrigated crops, pastures, grows in footpaths, and in gardens. It will tolerate acidic, neutral and basic conditions and will grow in semi shade to full sun.
It is considered a weed of many crops, particularly irrigated vegetable crops and sugar cane. This is in part due to its ability to reproduce rapidly by seed, going through several generations in one year. It is highly competitive and can spread quickly in a thick ground cover mat preventing the germination of native plant and crop seeds.
Potato weed, Galinsoga parviflora or Tridax parviflora, grows to a height of 75 cm (30 inches).
The stems are erect, branched, slender and striate (parallel ridged). The leaves are opposite, pale green and petiolate (with leaf stalk) and are toothed at the margins, lanceolate to ovate in shape. They are 1-6cm long and 0.5-4cm wide. The stems can be with or without hairs (glabrous). The leaf margins are fringed with short hairs like an eyelash. The upper leaves are usually smaller, narrower and sessile (without a stalk).
The flower heads are small with centres of yellow disk/tubular florets surrounded by several (usually 5) small white ray florets. The stalk of the inflorescence is slender and hairy. The flower head is 4-7mm in diameter with 2 or 3 rows of involucral bracts. The 5 inner bracts each support a ray floret. The fruit associated with the ray florets is an achene (a dry indehiscent 1-seeded fruit) that is 2mm long, slightly hairy, with or without a pappus of short bristles. The fruit associated with the disc florets is also an achene but it is 1.8mm long, slightly hairy, with a pappus of hairy-edged scales that are 1.5mm long. Flowers mainly during summer months. It is related to the Tridax daisy (another common weed.
The flowers are hermaphrodite (have both male and female organs) and are pollinated by Insects. The plant can also self-fertilize.
Potato weed can be controlled with herbicide or by cultivation. Hand pulling is possible but Potato Weed stems tend to break easily like Tridax Daisy stems do, so may be hard to remove. Follow up control is required due to the high production of seed which lie dominant in the soil. Disturbing the soil tends to increase seed germination.