||Asiatic citrus canker (ACC) is thought to have
arrived in Florida in 1992 or 1993 and has already claimed more than a million
commercial and residential citrus trees. A joint federal-state Citrus Canker
Eradication Program removes and destroys infected trees while scientists search
for new ways to stop this bacterial threat to Florida's $8.5-billion citrus
industry. Florida produces 75 percent of U.S. citrus. Worldwide, the United
States is second only to Brazil in citrus fruit production.
ARS researchers at the U.S.
Horticultural Research Laboratory in Fort Pierce, Florida, led by plant
pathologist Timothy R. Gottwald, have developed an early-warning system for
spotting new outbreaks. It uses a sentinel tree grid to detect and help prevent
the further spread of ACC into major citrus production areas along the state's
eastern central coast.
"The grid is formed by dividing each square mile into a 12-by-12 grid of
144 subsections. A sentinel tree is selected for repeated survey in each
subsection," explains Gottwald.
ACC moves primarily by wind-driven rain and raises brown blemishes surrounded
by an oily, yellow margin on citrus leaves and fruit. It causes fruit to drop
prematurely and lowers yields and quality. It can lead to a loss of markets due
to quarantines on the transport, sale, and export of fruit from affected areas.
The lime industry in south Floridathe only place in the United States
where limes are grown commerciallyhas been hardest hit. Early this year,
1,539 of the 3,000 acres of lime groves surveyed tested positive for ACC or
were exposed to the disease, according to the Florida Department of Agriculture
and Consumer Services. About 4,500 total citrus acres have been destroyed
throughout Florida so far.
"The sentinel tree grid is currently being implemented across the state in
high-risk residential areas such as Miami, where the most recent outbreaks have
occurred," says Gottwald.
By visually surveying the 1-mile-square gridded areas every 30 days,
researchers can identify new outbreaks and destroy infected trees quickly.
"The tree grid has helped us detect a number of new infections that
otherwise wouldn't have been found as early," says Gottwald.By Jesús
García, Agricultural Research Service Information Staff.
Timothy R. Gottwald is at
the USDA-ARS U.S.
Horticultural Research Laboratory, 2001 South Rock Rd., Fort Pierce, FL
34945; phone (561) 462-5883, fax (561) 462-5986.