A survey of the weed status and management of Leucaena leucocephala (Lam.) de Wit in Queensland, Australia
H. Max SheltonA, Scott A. DalzellA and Fiona L. McNeillB
A School of Land and Food Sciences, The University of Queensland, St. Lucia, Queensland 4072, Australia.
B Land Use Studies Centre, University of Southern Queensland, Toowoomba, Queensland 4350, Australia.
Surveys of Queensland local government shire councils and leucaena (Leucaena leucocephala) growers were conducted in August 2000, to ascertain the general distribution and level of weed leucaena populations in Queensland and to determine the incidence and degree of spread of leucaena from commercial leucaena/grass pastures.
Eighty-three of 125 shires (66%) responded reporting that leucaena was present in 60 (72%) shires. Thirty (50%) shires reported the presence of both cultivated and weed leucaena, 20 (33%) had cultivated only and six (10%) had weed leucaena only. Leucaena weed infestations were considered to be of 'minor' or 'no significance' in 80% of shires that reported leucaena was present. One shire, Calliope, viewed leucaena as a 'major' weed. The total area of weed leucaena in shires that responded ranged from 650-5650 ha. The total area of weed leucaena in the state was estimated to be in the range of 1000-9100 ha, compared to our estimate of 50 000-100 000 ha of cultivated leucaena. Leucaena infestations were reported to be localized and commonly occupied disturbed, ungrazed and riparian habitats, however nine (15%) shires reported leucaena had invaded undisturbed native habitats.
Seventy-three leucaena growers responded to the survey. Most had properties >2000 ha with >20-100 ha of cultivated leucaena, predominantly cvv. Cunningham and Tarramba. Forty-five per cent of leucaena plantings were <10 years of age, 48% 10-20 years of age and 6% >20 years of age. Growers viewed the current level of spread of cultivated leucaena as minor. Forty-two (58%) growers reported no spread, 23 (32%) had inter-row spread, seven (10%) had spread outside of paddocks but within properties while one observed spread outside his property boundary. Most growers did not control volunteer seedling recruitment. Mechanisms of seed dispersal were reported to be water, wind, animals and via cattle dung. There was no statistical relationship between incidence of spread and environmental parameters (soil type and annual rainfall) or specific grower management practices. There was anecdotal evidence that incidence of spread may increase with the age of leucaena plantings. At present, graziers considered cultivated leucaena a minor threat to the environment, as grazing appeared to control the level of seed production and volunteer seedling recruitment.
The results of these surveys indicate that at present, most local government weed control officers and commercial leucaena growers considered cultivated and weed leucaena were a minor environmental threat in Queensland. However, incomplete and sometimes inaccurate shire responses emphasized the need to educate local governments and communities regarding the identification and importance of potential environmental weeds. Immediate selective control of weed leucaena infestations in sensitive areas and support for the voluntary 'Code of Practice' initiated by The Leucaena Network was recommended.
Plant Protection Quarterly (2003) 18 (2) 42-47.