Little-Known Weed Causing Big Trouble in
Southeast By Sharon Durham
August 24, 2004
Like the plant in "Little Shop of Horrors," a little-known weed
is growing fast. Tropical spiderwort, inconsequential for seven decades, has
recently spread in alarming proportions in fields in Georgia, Florida and North
First detected in the United States in the 1930s, the weed has
made major gains in Georgia, according to Agricultural Research Service agronomist
Theodore Webster of the Crop
Protection and Management Research Unit in Tifton, Ga. Webster and his
colleaguesMichael Burton and Alan York of North Carolina State University, and Stanley
Culpepper and Eric Prostko of the University of
Georgiaare monitoring the weed's advances.
In 1999, it was found in five counties in southern Georgia. By
2002, 41 Georgian counties reported tropical spiderwort was present, and 17
listed it as moderate to severe.
A 2003 survey revealed that tropical spiderwort was entrenched
in Georgia, affecting 52 counties, with 29 counties listing the weed as
moderate to severe. More than 195,000 acres in Georgia are infested. It's now
widespread in Florida, and has been discovered on about 100 acres in Goldsboro,
Tropical spiderwort, Commelina benghalensis, is now the
most troublesome weed in Georgia cotton and the second most problematic weed in
peanut. The weed competes with crops for water and nutrients, and smothers the
crops at the same time. One reason for the surge in the weed's growth is its
resistance to the commonly used herbicide glyphosate. Conservation tillage and
reduced use of soil-applied herbicides may also be contributing to the problem.
According to Webster and his colleagues, tropical spiderwort
spread has coincided with resurgent cotton production in Georgia. Cotton
acreage in the state increased from about 260,000 acres in 1989 to nearly 1.5
million acres in 1995, in part due to the success of the boll weevil
eradication program. Most cotton grown in Georgia is tolerant to glyphosate,
allowing growers to spray the chemical on cotton crops to control weeds.
Webster and his colleagues are studying the biology and
management of tropical spiderwort and will continue to monitor its presence in
ARS is the U.S. Department of
Agricultures chief scientific research agency.