Navua sedge, a member of the Cyperaceae family, is an aggressive weed of pastures in Fiji, Sri Lanka, the Malay Peninsula, Vanuatu, Samoa, the Solomon Islands, and Tahiti and is now a weed of pastures and roadsides in north Queensland, Australia. Primarily restricted to areas with an annual rainfall exceeding 2,500 mm (98.4 in), Navua sedge is capable of forming dense stands, smothering many tropical pasture species. Seventeen herbicides were field tested at three sites in north Queensland, with glyphosate, halosulfuron, hexazinone, imazapic, imazapyr, or MSMA as the most effective for Navua sedge control. Environmental problems, such as persistence in soil, lack of selectivity, and movement off-site, may occur using some herbicides at the predicted 90% lethal concentration (LC90) control level rates. A seasonality trial using halosulfuron (97.5 g ai ha−1[1.4 oz ac−1]) gave better Navua sedge control (84%) by spraying in March to September than by spraying at other times (50%). In a frequency trial, sequential glyphosate applications (2,160 g ae ha−1) every 2 mo was more effective for continued Navua sedge control (67%) than a single application of glyphosate (36%), although loss of ground cover would occur. In a management trial, single applications of glyphosate (2,160 to 3,570 g ae ha−1) using either a rope wick, ground foliar spraying, or a rotary rope wick gave 59 to 73% control, whereas other treatments (rotary hoe, 3%; slashing, −13%; crushing, −30%) were less effective. In a second management trial, four monthly rotary wick applications were much more effective (98%) than four monthly crushing applications (42%). An effective management plan must include the application of regular herbicide treatments to eliminate Navua sedge seed being added to the soil seed bank. Treatments that result in seed burial, for example, discing, are likely to prolong seed persistence and should be avoided. The sprouting activity of vegetative propagules and root fragmentation also needs to be considered when selecting control options.

The liana, hiptage (Hiptage benghalensis), is currently invading the wet tropics of northern Queensland and remnant bushland in south-eastern Queensland, Australia. Trials using seven herbicides and three application methods (foliar, basal bark, and cut stump) were undertaken at a site in north Queensland (158 700 hiptage plants ha -1 ). The foliar-applied herbicides were only effective in controlling the hiptage seedlings. Of the foliar herbicides trialed, dicamba, fluroxypyr, and triclopyr/picloram controlled >75% of the treated seedlings. On the larger plants, the cut stump applications were more effective than the basal bark treatments. Kills of >95% were obtained when the plants were cut close to ground level (5 cm) and treated with herbicides that were mixed with diesel (fluroxypyr and triclopyr/picloram), with water (glyphosate), or were applied neat (picloram). The costings for the cut stump treatment of a hiptage infestation (85 000 plants ha -1 ), excluding labor, would be $A14 324 ha -1 using picloram and $A5294 ha -1 and $A2676 ha -1 , respectively, using glyphosate and fluroxypyr. Foliar application using dicamba for seedling control would cost $A1830 ha -1 .The costs range from 2-17 cents per plant depending on the treatment. A lack of hiptage seeds below the soil surface, a high germinability (>98%) of the viable seeds, a low viability (0%) of 2 year old, laboratory-stored fruit, and a seedling density of 0.1 seedlings m -2 12 months after a control program indicate that hiptage might have a short-term seed bank. Protracted recolonization from the seed bank would therefore be unlikely after established seed-producing plants have been controlled.

Summary The perennial shrub Siam Weed (Chromolaena odorata (L.) R. M. King & H. Rob.), a native of the rainforests of central and southern America, is predicted to invade most countries between the Tropics of Cancer and Capricorn. Subsequent to its discovery in northern Queensland, Australia in 1994, it was unsuccessfully targeted for eradication, with early control efforts restricted to manual removal and foliar spraying with triclopyr/picloram. A chemical trial involving five herbicides and three application methods (foliar, basal bark and cut stump) was undertaken in northern Queensland to identify effective chemicals to control this weed. Of the foliar herbicides tested, fluroxypyr (70 g/100 L) provided 99% mortality, triclopyr/picloram (105/35 g/100 L) 95%, while metsulfuron‐methyl (9 g/100 L) killed 85% of the treated plants. The herbicides fluroxypyr (300 g/100 L), picloram (43 g/1 kg) and triclopyr/picloram (400/200 g/100 L) killed greater than 98% of the plants when applied as basal bark or cut stump. The integration of fire into the management strategy either as a primary or secondary control option could have a major role, given that in this study, 99% of the Siam Weed soil seed bank was located on the soil surface.