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Early-Warning System to Detect Spread of Asiatic Citrus Canker

By Jesús García
June 20, 2000

The thunderstorms that often rage during sultry summertime afternoons in subtropical Florida have exacerbated the spread of Asiatic citrus canker (ACC). This bacterial disease now threatens the state’s multibillion dollar citrus industry.

Scientists with the Agricultural Research Service’s U.S. Horticulture Research Laboratory in Ft. Pierce, Fla., led by plant pathologist Tim Gottwald, have developed a new strategy for detecting ACC infestations. The disease--primarily spread by wind-driven rain--is thought to have arrived in south Florida in 1992 or 1993. It has spread to more than 1,200 square miles of citrus-producing areas around the state.

ACC causes brown blemishes on citrus leaves, twigs and fruit, resulting in fruit drop, loss of yields and quality. This leads to a loss of local, national and international markets due to quarantine restrictions.

The new early-warning system for ACC will be used in a statewide survey to detect the disease. Gottwald’s study determined that a 1,900-foot zone is required to limit further spread of the disease. The study also recommended that a “sentinel tree grid” be established to detect and prevent the further spread of ACC into major grapefruit production areas. Florida produces 75 percent of U.S. citrus. Worldwide, the United States is second to Brazil in citrus fruit production.

The 15-mile wide by 20-mile long sentinel tree grid comprises 144 existing dooryard trees of susceptible cultivars arranged in a 12-by-12 pattern covering each square mile of the area directly north of the Miami Dade and Broward county infestation. Trees within the grid are 450 feet apart. By making a visual survey of the grid every 30 days, scientists will be able to see if any new ACC outbreaks have occurred after eradication of the initial outbreak.

These findings have led to an increase in the ACC eradication budget to $175 million, with an additional $40 million for payments to growers hit by the disease.

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

Scientific contact: Tim R. Gottwald, ARS U.S. Horticultural Research Laboratory, Ft. Pierce, Fla.; phone (407) 897-7347, fax (407) 897-7309,