Early-Warning System to Detect
Spread of Asiatic Citrus Canker
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 states multibillion dollar citrus industry.
Scientists with the Agricultural Research
Services 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
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. Gottwalds 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
ARS is the chief research agency of the U.S.
Department of Agriculture.
Scientific contact: Tim R. Gottwald, ARS
Research Laboratory, Ft. Pierce, Fla.; phone (407) 897-7347, fax (407)