|June 2007. A weed was reported from Palau with an inflorescence very similar to that of Chromolaena odorata, but the plant is much smaller and more herbaceous. It also has a strong odor, but not as unpleasant as Chromolaena. The plants were about ?? m or less tall. It is a small patch and it does not appear to have produced any seed yet, so the plants will be uprooted and destroyed. The entire 53-mile length of the road will be inspected to see whether there is more of it.
There were several suggestions as to its identification:
Eventually, it was identified in Australia as Praxelis clematidea a close relative of Chromolaena. It comes from South America and the only places it is known to occur outside its native range are: Queensland (where it may have arrived as a contaminant of the same seed batches that introduced Chromolaena); Hong Kong and the adjacent part of south China and Macau. In Queensland, while it was first recognised in the Innisfail area in 1993, it has spread like wildfire and occurs patchily (but often abundantly) from the Torres Strait Islands to just north of the Sunshine coast.
In the Innisfail area there was concern initially as entire areas became carpeted in the weed; however, it does not appear to be much more of a problem than the blue top, Ageratum species, which was present earlier and growing in similar situations. The local IPM officer, however, suggested it has the propensity to grow more as a biannual than the shorter lived Ageratum. It is very easy to control with glyphosate sprays, but it is best to apply contact herbicides before systemics. Praxelis has similar textured leaves and an odour when crushed similar to cat urine and probably will behave similarly to Ageratum where fires occur; ie it is somewhat fire resistant. While this may not be pertinent on Palau, in the local area (Australia) cane growers find difficulty when they want to burn a cane paddock where there is a lot of Ageratum growing.
Watch for new sprouts from the collar a couple of weeks after the aerial parts have died from the contact herbicides. In manual weeding, make sure that the uprooted clumps (with the soil knocked off) are heaped together in an exposed area and allowed to dry. Seeds are moved easily in the wind and on socks.
There is a very good fact sheet on Praxelis at: www.environment.gov.au/biodiversity/invasive/weeds/weeds-alert/pubs/p-clematidea.pdf
The weed can become a serious problem in slighly acidic and moist soils in tropical and sub-tropical conditions, but can be managed well with an understanding of how it thrives.
See the PIER website: