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Citrus Canker: A Blemish of Epic Proportions

March 7, 2013

Five Hundred Years of Florida Flora Firsts: How Plants have shaped Florida’s History

Since the 1800s, changes in climate and weather events have shaped the geography of citrus in Florida. Sometimes these forces have combined with pests and diseases to exacerbate threats to the state’s most recognizable crop. This has been the case with citrus canker, a disease that has now become endemic to our state.

(Download a detailed history of citrus canker in Florida here.)

 

From the early Twentieth Century to the present, Florida’s citrus industry has grappled with citrus canker, a disease that causes lesions on leaves, stems and fruits of citrus trees. The disease is not harmful to humans, but causes leaves and fruit to drop prematurely. Infected fruit, while safe to eat,  is unsuitable for sale. Trees eventually succumb to the disease

From mystery disease to serious threat

Citrus canker emerged in Florida in 1912 when Dr. Edward Berger, a University of Florida entomologist working to certify plants for shipment, found a mystery disease in a Monticello citrus nursery.  Eventually identified as citrus canker, it would plague the citrus industry in Florida to the present day.

CitrusCanker2

Citrus canker causes blemishes on leaves, fruit and stems. Harmless to humans, the disease renders fruit unmarketable.

The disease, Xanthomonas campestris pv.  citri , is caused by a bacterium.  Signs include blemishes on leaves, fruit and stems. Canker outbreaks generally occur when new shoots are emerging or when fruit is in the early stages of development, especially if a major rainfall event occurs during this critical time. Frequent rainfall in warm weather, especially storms, contributes to disease development.

Probably imported about 1910 on citrus from Japan, canker became established in the gulf states of Alabama, Louisiana, Mississippi, Texas and Florida, as well as Georgia and South Carolina. By 1914 Florida growers and shippers, recognizing the potential threat it posed to the industry, contributed funds for an initial investigation and additional inspectors. By late 1914, it was obvious that curative measures, which included pruning, defoliating and painting with carbolineum, were not working. Growers began burning canker-infested trees in place.

Scientists learned that sanitation was an important component of containment and eradication.  Growers began disinfecting people, clothing and equipment, practices that would be replicated in future outbreaks.

By the time the Florida Legislature convened in 1915, canker was recognized as a serious threat to the industry and the Legislature passed the Florida Plant Act of 1915. This legislation established the State Plant Board, the predecessor of the Florida Department of Agriculture and Consumer Services Division of Plant Industry (DPI). By September, the Plant Board occupied offices at Anderson Hall at the University of Florida in Gainesville.

AndersonHallUF

Anderson Hall at the University of Florida was the first home of the Plant Board.

The Plant Board took over the inspection force of the Grower’s and Shipper’s League. The board hired apprentices, who trained on citrus canker at their own expense. This program lasted from 1915 until eradication was declared in 1933. By then it had cost Florida more than $6 million (in 1934 dollars) to save the $500 million industry.

1984: The nursery strain

After citrus canker was detected in Ward’s Nursery in Avon Park in 1984, about 20 million citrus plants were destroyed. Then scientists determined the state was dealing with a different strain of citrus canker, one less virulent that the one that had plagued the industry in the 1930s. This strain, dubbed the “nursery strain,” was as a less-serious threat. Some scientists even wanted to rename it “citrus bacterial leaf spot” to differentiate it from the virulent Asian strain of canker

 Asian strain appears yet again

The Asian strain was detected once again in 1986 on residential citrus on Anna Maria Island on the gulf coast. Dooryard and grove surveys detected it in Manatee, Pinellas, Sarasota and Hillsborough counties. Again, infected trees were destroyed and in 1994, after nine years, officials declared citrus canker eradicated in Florida. Three years later the disease re-emerged in the same general area. By that time, the industry was engaged in a far larger eradication program.

1995 to present

In October 1995 canker had been detected in residential and commercial citrus in urban Miami-Dade County. DNA profiles showed this outbreak to be unrelated to the 1986 infestation.  Experts believe the majority of the outbreaks of citrus canker in Florida after 1997 resulted from a single introduction in the Miami area.

In February 2000, Governor Jeb Bush declared a state of emergency for canker-infected counties and allocated additional funding for eradication. A cooperative state/federal eradication program, the Citrus Canker Eradication Program (CCEP), was established. Officials began complying with a rule requiring removal of citrus trees within 1900 feet of a confirmed canker find, a rule that became a state law in 2002. A two-year epidemiological study had demonstrated that more than 95 percent of the disease from infected trees was contained at that distance.

Because the outbreak originated in urban areas, eradication efforts affected not only commercial growers but also hundreds of thousands of urban homeowners. Some of these homeowners whose dooryard fruit trees were destroyed took their dissatisfaction with the program and the compensation it offered to the courts.

Within a year, various legal challenges concerning the 1900-foot rule were restraining the program from cutting exposed trees. Predictably, the year 2002 witnessed an explosion of new infections.

Eventually the infestation would encompass residential and commercial citrus in Miami-Dade, Brevard, Broward, Clay, Charlotte, Collier, De Soto, Glades, Hardee, Hendry, Highlands, Hillsborough, Indian River, Lee, Manatee, Martin, Monroe, Okeechobee, Orange, Osceola, Palm Beach, Polk, St. Lucie andSarasota counties.

Hurricanes end canker eradication efforts in Florida

2004hurricaneEmphasis shifted from eradication to controlling and living with citrus canker in 2006, when the U.S. Department of Agriculture declared citrus canker endemic to Florida. Hurricanes in 2004 and 2005 had spread canker throughout the state, so extensively that eradication became impossible. In January 2006, the U.S. Department of Agriculture discontinued funding for the program, effectively bringing it to an end. More than 16.5 million citrus trees in groves, nurseries and backyards had been destroyed in what had been the world’s largest pest eradication program.

Emphasis shifts to management of diseases

By January 2006, all CCEP activity had ended. Although commercial surveys continue for fruit certification, the emphasis is now on managing canker and other diseases. Toward that end, the Florida legislature established the Citrus Health Response Program (CHRP), requiring the Florida Department of Agriculture and Consumer Services Division of Plant Industry to create rules to protect citrus health in Florida. New rules for shipping fresh citrus from Florida were adopted in 2009.

Meanwhile, an even greater threat looms for Florida citrus producers: a disease that has compromised citrus production everywhere in the world where it has appeared. Our next entry in this series will tell the story of the disease known variously as Huanglongbing, HLB, or citrus greening.

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During 2013, this blog will review plants that, for better or worse, have helped form the history of our state. We will be drawing on expertise of our DPI scientists and we invite everyone to participate. There are fascinating stories to be told, and we will welcome your participation in the form of questions and comments.

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