Little-Known Weed Causing Big Trouble in Southeast

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 Carolina.

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 colleagues—Michael Burton and Alan York of North Carolina State University, and Stanley Culpepper and Eric Prostko of the University of Georgia—are 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, N.C.

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 the Southeast.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.