Yellow soldier has since become a problem weed and is spreading through tuart (Eucalyptus gomphocephala) and banksia woodlands on sandy calcareous soils. It could become a significant environmental problem because it replaces native herbs and annuals in both disturbed and relatively intact bushland. Yellow soldier produces a large number of viable seeds that germinate each year, leading to rapid expansion of populations that are difficult to control.
In its native range the genus Lachenalia extends mainly throughout western and southwestern Cape Province in South Africa. It occurs as a serious weed at a number of conservation reserves around Perth, Western Australia. It invades banksia/ tuart woodlands and limestone scrub and heath around the Swan estuary, banksia/jarrah woodland to the south and west of Perth, and tuart woodland up to 40 km north of Perth.
With only a single annually renewed bulb, yellow soldier spreads mainly by seed. There are usually between one and ten flowers per plant and each flower produces a capsule that contains 40–60 seeds, potentially giving rise to infestations of more than 400 bulbs per square metre. Experience suggests that seed is not easily spread over long distances. Water movement and human activity are the main causes of seed spread. Yellow soldier seeds often germinate in response to fire, taking advantage of any bare ground and the reduction in competition from native species. Plants have also been observed to produce a prolific number of bulbils (small bulbs) around the base of stems left lying on the soil surface, but this does not appear to be a common method of reproduction or dispersal.
Yellow soldier belongs to a group of South African plants, many of which are grown as garden ornamentals. Three other species of Lachenalia are weeds of Western Australia.
Yellow soldier has two strap-shaped leaves, 60–350 mm long and 15–25 mm wide, which grow upwards from the base. The leaves are slightly V-shaped in cross-section. The bright yellow flowers are 25 mm long and more or less tubular in shape but swollen in the middle. They grow on short stalks just 45–100 mm above the ground.
Yellow soldier stores food material for the next growing season in bulbs, which are short underground stems.
Large healthy plants can produce up to ten yellow upright flowers. Plants flower particularly well following fire and set prolific amounts of seed.
The smooth, shiny black seeds are about 2 mm long. The seed does not appear to remain viable in the soil for more than two or three years.
In its native range the genus Lachenalia occurs in areas with winter rainfall, undergoing long dormant periods over the dry summers. In Australia it has invaded woodlands and limestone scrub areas.
CRC for Australian Weed Management: Kate Brown (Environmental Weeds Action Network), Greg Keighery (CALM WA), Sandy Lloyd (Agriculture WA/Weeds CRC) and John Thorp (National Weeds Management Facilitator).
There are a number of difficulties associated with controlling bulbous weeds such as yellow soldier growing in native vegetation. Because there are relatively few yellow soldier 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 yellow soldier without their expert assistance. Control effort that is poorly performed or not followed up can actually help spread the weed and worsen the problem.
In sandy soils bulbs can be removed by hand in late August – early September by cutting the roots with a knife and pulling them out with the bulb. However, hand removal is difficult and time consuming, and can cause major soil disturbance which may encourage other weeds. It is often impractical on a larger scale, especially given the high density at which these bulbous weeds often occur.
Yellow soldier appears to be tolerant of fire and regenerates soon after bushfire. Plants appear to flower particularly well following fire, setting prolific amounts of seed. In addition, fire reduces competition from native vegetation and creates bare areas where seed can germinate. However, fire can create opportunities for land managers to prevent further spread and establishment. After fire, yellow soldier’s flowers are clearly visible, and the reduced cover of native vegetation makes the resprouting flowering bulbs easy targets for herbicide control.
Once the initial infestation is controlled, follow-up monitoring and control will be required to ensure that reinfestation does not occur.
Yellow soldier (Lachenalia reflexa) is not declared in NSW under the Noxious Weeds Act 1993.