Citrus Canker – Is eradication the only solution?

The President’s Hoot
Richard H. Baker, Ph.D.
September 2005

I am very concerned about the loss of commercial citrus groves and agricultural lands due to the current citrus canker eradication program. The burning and disking associated with eradication may be a temporary solution that may severely impact wildlife and the fragile Indian River Lagoon environment and pave the way for housing developments and excessive population that will ultimately replace them. The organism causing canker is a bacterium called Xanthomonas axonopodis pv citri (Xac), which most likely originated in southeast Asia and has spread worldwide, primarily to warm, moist, coastal regions, generally vectored by wind driven rain, human movement, and sometimes by insects and birds. The canker disease is not usually fatal to the tree, but the damaging effects range from leaf damage and fruit blemishes to some defoliation, twig dieback, and fruit drop. Options for canker control include spraying copper fungicides, pruning affected shoots, and installing windbreaks.

About 1912, canker first appeared in Florida when introduced on infected seedlings from Japan. In 1933, canker was declared “eradicated” from Florida. Infestations were again found in 1986, mostly along the Gulf Coast, but after destroying many thousands of infected and exposed trees, eradication was prematurely declared in 1994. However, a year later, in 1995 more canker (although its DNA was different) was found in Miami, and again in 1997 in Manatee County on the Gulf Coast. Thus, canker is not a stranger to Florida, and one would even expect it since a susceptible monocultural crop of citrus, present in large areas year after year for over a century provides an ideal habitat for the plant pathogen. Additional information can be found on the Internet, e.g.

In 2000, the state legislature passed the “1900 foot rule”, which stated that all trees within a 1900-foot radius of an infected tree shall be removed and destroyed. In practice, this amounts to about 260 acres or a little less than ½ of a square mile (0.41). Owners of grapefruit acreage are compensated at $27 per tree destroyed up to $2704 per acre for the trees and $3,342 per acre for the crop for a total of up to $6,046 per acre. With the recent hurricanes, canker has been found in many locations throughout the state with numerous finds in St. Lucie, Martin and Indian River Counties. View a map below of canker exposure areas on the Treasure Coast.

Besides pushing and burning infected and neighboring trees, the state is requiring that these citrus lands be disked four times with a 24 inch disk to a depth of 10 inches to insure that there will be no regrowth from citrus trees roots. Extensive disking will cause enormous damage to our soils by disturbing surface soil structure and organic material with further damage by extensive soil erosion. Off-site sediment movement will pollute our streams and waterways and ultimately, the Indian River Lagoon. Studies have shown that certain agricultural pesticides are bound to clay and organic soil components and if disturbed by aggressive disking, may be carried by surface water to the Indian River Lagoon. Regrettably, this is now occurring when agricultural land is leveled and converted into subdivisions. Fortunately, there are ways to disk the tree rows to kill roots and avoid regrowth while leaving the grassed furrows and swales intact to prevent soil erosion and offsite sediment movement. But will this be done?

Moreover, if the current citrus acreage destined for removal is over 20% as the report at the above website for St. Luce County indicates, should the Department of Agriculture and Consumer Services reconsider the logic of the 1900 ft rule? This rule was based on a study in a South Florida urban setting with typical thunderstorm weather patterns and not a rural setting impacted by three major hurricanes. Will they continue to push and burn citrus trees until the last tree is standing, and if infected they will have to destroy that as well? So much of our economy and our environment depend on the citrus industry. Should we destroy our citrus groves without reassessing the science and the economic repercussions to our county and state?

Also disturbing, there are many abandoned citrus groves especially within the Urban Service Area that are not being inspected, and thus may be harboring not only canker but also other pests and diseases. Even more troublesome is the likelihood of future introductions of canker bacteria arising from the illegal entry of infected plant materials brought into our state by international travelers arriving each day. We have had canker introduced in the past this way, and why should we not expect it again?

Perhaps citrus canker management is a desirable alternative to eradication. Scientists will now be able to conduct canker research here in Florida, to develop resistant varieties, and test new control strategies and products. This might provide a long-term solution to citrus canker instead of the current dubious approach that appears to be failing and is further jeopardizing an already weak citrus industry. What percent of the citrus groves need to be burned before we stop?

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