tropical spiderwort

Scientific name: Commelina benghalensis (L.) (Commelinaceae)

Domestic Programs Pest Evaluation. Arthur E. Miller, USDA-APHIS-PPQ, AERO, Raleigh, NC. November 26, 2001

Physical description: Tropical spiderwort is an annual or perennial creeping herb with white, burrowing rhizomes which produce underground flowers, fruits, and seeds; stems are fleshy, succulent and freely branching up to 3 feet long, usually hirsute, rooting at the nodes, the lower nodes usually developing naked underground shoots bearing small, white flowers; leaves simple and alternate, with closed sheaths often with reddish hairs; and flowers zygomorphic with the anterior (lower) 3 petals (sometimes white) much smaller than the 2 posterior (upper) lilac or bluish ones; seeds rugose-reticulate and often appearing sugar-coated.

Origin and North American Distribution: Tropical spiderwort is found in much as Africa, Saudi Arabia, India, Pakistan, Southeast Asia, the Pacific Islands to Australia, Cuba, Jamaica, the West Indies, Brazil, and French Guiana. In the U.S., it has been found in AL, CA, FL, GA, HI, LA and recently NC.

Quarantines: Tropical spiderwort (also called Benghal dayflower) is a Federal Noxious Weed.

Dispersal: The plants reproduce by seeds, stolons, and rooting at nodes of stems. One plant can produce as many as 1600 seeds.

Control: Property managers and cooperators may use these strategies:

Cultural Control. Plants readily root at the nodes of the creeping stems, especially when cut or broken, making these weeds difficult to control in field areas. Sections on the soil surface root readily during rainy weather or in the shade of crop plants.

Chemical Control. University of Florida tests conducted in 2000 showed that Command and Spartan used in combination or alone were effective April to early June, but effectiveness trailed off later in the season. Methods Development has found that 46 brands of herbicide are labeled for use on dayflower. However, farmers in Florida have not been able to control tropical spiderwort effectively with chemicals. Control with herbicides is difficult because many seeds germinate after the initial flush of summer weeds and part of the seeds are produced underground.

Biological Control. None is known.

Economic impact: Tropical spiderwort is a major host of cucumber mosaic virus. CMV is spread to tobacco by green and red aphids. Both spiderwort and CMV have continued to spread in Florida. The disease threatens entire tobacco crops in Florida because farmers cannot control it effectively with chemicals. Tropical spiderwort is an alternate host of peanut rosette virus, the fungal disease Puccinia commelinae, and the nematode Meloidogyne incognita.

Tropical spiderwort forms, dense, pure stands, smothering out other plants, especially low-growing crops. It has been reported recently as a problem in cotton in Alabama. In pastures, it grows rapidly over desirable grasses and legumes, competing with them for light and nutrients. In rice and other lowland crops it may be almost subaquatic withstanding flooding and waterlogged conditions, but they can also be found in cultivated lands, field borders, gardens, grasslands, roadsides, and waste places, and can become the dominant species in pastures.

Environmental impact: Tropical spiderwort is a weed of moist areas in the tropics and subtropics. It is classified as a wetland hydrophyte (plant which can take root in water-saturated soil), but the plant can live for extended periods after the soil has dried out. Tropical spiderwort grows from sea level to 1300 m elevation.

Benefits of control: Agricultural, forest, urban and natural areas can benefit from control and prevention of further spread of this FNW.