Imported weed is one of the worst
LEUCAENA leucocephala is a small, fast-growing large shrub to small tree native to southern Mexico and northern Central America.
It was first recorded in Australia at the end of the 19th century after being imported as part of cattle fodder and from cattle waste.
Leucaena leucocephala was deliberately imported last century as cattle fodder, fuel wood, shade, food and green manure, but is now a visible weedy shrub, mostly found along roadsides, river banks, and in disturbed sites such urban development or road works.
Leucaena is a small tree that has been planted for fodder in many tropical areas of the world, including Queensland. In inland central Queensland in the Emerald region half a million hectares have been planted for cattle fodder.
A survey in 2005 estimated 1000-9000ha in Queensland is infested by leucaena species.
It is ranked number 41 in the list of 200 serious environmental weeds of south-east Queensland.
Planted or weedy leucaena was found in 60 of the 83 shires in Queensland. Nineteen shires reported that leucaena infestations had existed in their shire for 10-50 years. Eighteen local regional councils consider leucaena a pest plant worth listing in their environmental weed plans. This weed problem will be exacerbated by the current use of leucaena by some people in the community as a garden planting
L. leucocephala is considered one of the 100 worst invasive species by the Invasive Species Specialist Group of the IUCN.
It is classified among the 12 worst pests out of 86 introduced species in Hawaii.
In Queensland leucaena species has become a "conflict tree", primarily because leucaena is grown and used by pastoralists in central Queensland as cattle fodder. Many leucaena seeds are transported and dropped from truckloads carrying bales of cattle fodder, or from cattle waste from cattle trucks or rail wagons along the sides of the rails or roads where they become an environmental pest and erosion problem, especially on river banks or other moist areas.
Leucaena is a serious environmental weed that forms dense thickets excluding other plants and destroying any ground cover (grass) exposing the soil to erosion.
Leucaena grows in areas with more than 650mm rainfall per year, are frost and fire sensitive and prefer deep, well-drained, slightly acid to alkaline soils. Two subspecies (ssp.), L. glabrata (the preferred fodder ssp.) with hairless new growth, and L. leucocephala with hairy new growth, are grown in Australia. Both species are weedy and have become a environmental problem.
Four other species in the genus, L. Lanceolata , L. pulverulenta, L. shannonii and L. Trichodes ,are known to demonstrate weedy tendencies, spreading and colonising sites such as roadsides and abandoned fields within their native ranges
It is possible that spontaneous hybridisation between introduced species are a possible additional hazard posed by leucaena
The weediness of Leucaena leucocephala ssp is attributed to its abundant, massive year-round seed production, build-up of a substantial seed bank, ability to re-sprout from cuttings or after burning, drought tolerance, ability to produce thickets, and ability to spread from an isolated tree.
The seeds are spread by mud on road maintenance equipment, cattle manure, wind, in water and movement of contaminated soil, hay and machinery. Unless leucaena is heavily grazed or controlled, it spreads rapidly to adjacent areas. It shades out all ground cover creating a environment for erosion of the soil under the lecucaena.
Control is to hand-pull small, individual plants and take care to remove the roots to prevent regrowth. Herbicides are effective.
Shrub or tree to 10m (rarely to 20m) high. Bark smooth with prominent raised areas (lenticels).Young branches finely hairy to hairless.
Leucaena leucocephala has spineless; leaves bipinnate, leaf axis (rachis) 4.5-14 cm long, pinnae in 3-10 pairs, leaflets 5-21mm long, 1-5mm wide in 5-22 pairs, hairless or margins with fine very short hairs, gland often at or below junction of the lowest pinnae pair; flowers bisexual, stamens 10, anthers hairy
Flowers/seedhead occur in heads 1.2-2.1cm wide, green to whitish, over 80 flowers per head, 1-3 heads in leaf axils or several in terminal racemes, on stalks 2-6.5cm long and flowers summer and autumn.
Seed pods are 8-22.5 cm long, 1.3-2.7cm wide. Seeds are 5-10 mm long and 3-6 mm wide, glossy, and brown.
Ian Read can be contacted 074159 9365, or email ian.read7@bigpond .com.au for free weed identification, free weed presentations and native plants advice, and for landscaping and weed control.