Growers and gardeners in the South-east of the United States are facing a fast-spreading weed called Tropical Spiderwort, Commelina benghalensis. It is also known as Benghal Dayflower. This native of Africa and south Asia was first observed in Florida in 1928. It advanced into Georgia, but was not considered a troublesome weed until 1999.
The main reason Tropical Spiderwort has become a serious weed has to do with recent changes in commercial cropping systems. The biggest of these is the widespread use of Round-up-ready crops. This technology helps growers to better manage weeds, but Commelina has a natural tolerance to glyphosate - the active ingredient in the herbicide Round-up, so it is adapted to that change. It also tolerates other common herbicides.
The impact of Tropical Spiderwort has recently moved beyond open field crops. In autumn 2005, container ornamentals contaminated with the weed were discovered in retail outlets in North Carolina. The plants had been shipped from a South Carolina nursery. Tropical Spiderwort is on the Federal Noxious Weed List, meaning that movement across state boundaries is prohibited. Halting further spread of this weed is crucial in minimizing control costs throughout the region.
So how do you spot tropical spiderwort? "The easiest way to identify it is by the presence of underground flowers," says Agricultural Research Service scientists "Of the 250,000 species of flowering plants, only 36 have underground flowers. Tropical Spiderwort is the only known day-flowering species in the United States with underground blossoms."
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