Tomato spotted wilt virus targeted

When it comes to controlling one of the world's most troublesome insect pests — and the deadly plant virus it spreads — researchers with the University of Florida's Institute of Food and Agricultural Sciences say pesticides are out and new environmentally friendly management programs are in.

During the past two decades, tomato spotted wilt virus has been spread around the world by tiny insects called thrips, causing millions in losses to a variety of vegetable, ornamental and agronomic crops.

"Epidemics of tomato spotted wilt have been troublesome throughout the southern United States, cutting yields by 20 percent to 30 percent on tomatoes," says Steve Olson, a professor of horticulture at UF's North Florida Research and Education Center in Quincy. "In Florida and Georgia where tomatoes and peppers are valued at about $1 billion annually, farmers have been hit hard. The virus also affects peanuts, tobacco and other crops."

It can turn leaves brown, purple or bronze and frequently kills the stem tips on plants. The virus also can cause brown or yellow spots and rings on tomatoes and other produce, making them unappealing to consumers and therefore unmarketable.

The virus is transmitted from plant to plant almost exclusively by several species of thrips. The western flower thrips (Frankliniella occidentalis) and the tobacco thrips (F. fusca) are major species in Florida.

Until now, growers responded by spraying toxic, broad-spectrum insecticides in an attempt to control thrips, but the chemicals do not prevent transmission of the virus. The solution, according to researchers at the Quincy center, is to use a variety of new environmentally friendly strategies known as integrated pest management, or IPM.

IPM includes new cultural practices, natural insecticides, bio-control agents or natural predators and a new treatment that boosts the plant's immune system against viruses and bacterial diseases.

"In north Florida and south Georgia, the incidence of tomato spotted-wilt virus on tomato plants has been reduced by as much as 75 percent with a new plastic bed cover that reflects ultraviolet (UV) light and repels thrips," says Tim Momol, an assistant professor of plant pathology at the Quincy center.

"Instead of covering tomato plant beds with the standard black plastic mulch, many growers have switched to the UV-reflective mulch, boosting tomato yields by as much as 600, 25-pound boxes per acre and increasing profits by as much as $4,000 per acre," Momol says.

"While the reflective mulch costs an extra $200 per acre, yield increases and higher returns justify its use," Momol said.

Dale and Greg Murray, owners of Murray Farms in Bainbridge, Ga., started using the UV-reflective mulch on their 32-acre tomato field in 2000. Dale Murray says the incidence of tomato spotted wilt virus was reduced from as much as 45 percent to 11 percent, boosting farm income by about $1,000 per acre.

Joe Funderburk, a professor of entomology at the Quincy center, says a recent survey showed about 30 percent of the growers in north Florida and Georgia are using the UV-reflective mulch. Its use is expanding to other production areas in the Southeast in 2003.

He says a natural insecticide called spinosad, which poses little threat to field workers or the environment, also is helping growers control thrips on tomatoes. And, a new immune-boosting treatment, which is marketed under the Actigard trademark, is now being used by about 45 percent of all tomato growers in the region.

"To control the virus on peppers, we're recommending the use of a naturally occurring predator called the minute pirate bug that attacks thrips," Funderburk says. "Nearly 100 percent of all pepper growers in North Florida and South Georgia are using the beneficial bug, cutting pesticide costs by $100 per acre and boosting crop yields by as much as 40 percent."

Unfortunately, the minute pirate bug is not effective against thrips on tomatoes because the plants are toxic to the natural predator, he says.

Tommy Smith, owner of Thomas Smith Farms in Quincy, was the first pepper grower in the state to use the minute pirate bug in 1997. Before he began using the natural predator, Smith lost two consecutive crops to thrips and tomato spotted wilt virus. Use of the biological control has reduced thrips populations by "at least 75 percent" in his pepper fields and eliminated the need for insecticides, he says.

Glades Crop Care Inc. in Jupiter, Fla., the largest consulting company in the Southeast, also uses the pest control program on all of their acreage in Georgia and Florida. Adoption of the program is expanding rapidly throughout much of the southern United States and many other regions of the world, says Madeline Mellinger, president of the firm.

Olson, Momol and Funderburk developed and promoted the new IPM control measures, and the researchers are collaborating internationally so that the program is adopted in other countries.

The research is supported with funds provided by the Gadsden County Tomato Growers Association and Florida Tomato Committee. The U.S. Department of Agriculture's Cooperative State Research, Education and Extension Service (CSREES) funded a grant to implement the program on tomatoes, peppers and other crops. Research and implementation of the program in the Caribbean Basin is supported by a USDA Special Grant.

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