North American Fruit Explorers mailing list at ibiblio

["J. Rosano II" <GIANNI-2@prodigy.net>]

Dear Folks:

Thought you may find this interesting...
 
 Published Wednesday, June 21, 2000, in the Miami Herald
 
 Canker fighters review options
 Choices beyond cut-and-burn are investigated
 BY MARTIN MERZER
 mmerzer@herald.com
 
 FORT PIERCE -- Alarmed by the tenacity of citrus canker as it marches
 through Florida, state and international scientists debated a radical
new
 approach Tuesday that could spare some of the millions of seemingly
doomed
 trees in South Florida.
 
 Maybe, some experts say, Florida will have to concede defeat, accept
the
 inevitable.
 
 Maybe we must live with the disease -- controlling it with chemicals,
 windbreaks, frequent inspections and other relatively elegant measures
--
 instead of invading yards and groves in a primitive attempt to root it
out
 with bulldozers, chain saws and bonfires.
 
 Among the promising avenues of research revealed during an
unprecedented
 international canker summit: seven new ``induced systemic resistance''
 compounds that can be sprayed on trees and might act as serums to
enhance
 the resistance of citrus trees.
 
 Canker management programs already are working in Brazil and Argentina
and
 have largely replaced tree eradication campaigns there, about 80
scientists
 and citrus industry executives were told during the International
Citrus
 Canker Research Workshop.
 
 ``Control programs are an option for Florida,'' said Wayne Dixon, a
state
 canker expert and an organizer of the three-day event. ``We're still
into
 eradication, but we want to see what else is out there.''
 
 Programs to coexist with canker -- tolerating it at certain levels --
have
 never been tried or seriously considered in Florida. That is changing
as
 scientists search for a way to control the bacterial disease without
 sacrificing more trees.
 
 State workers already have destroyed nearly half a million citrus trees
in
 South Florida and many more are on the chopping block.
 
 ``I'm known as `Satan' in Dade County,'' said Craig Meyer, the state's
 deputy commissioner of agriculture, who runs the eradication program in
 Miami-Dade and Broward.
 
 Florida's current program, widely criticized as barbaric and wasteful,
 condemns every infected tree and every other ``exposed'' citrus tree
within
 1,900 feet of it.
 
 It does not appear to be working. Despite eradication and a quarantine
that
 blankets most of Broward and Miami-Dade, the disease already has spread
to
 Palm Beach County and Collier and Hendry counties in Southwest Florida.
 
 Next in line: Central Florida's sprawling groves, which produce nearly
$8.5
 billion worth of citrus every year.
 
 Harmless to humans, canker severely blemishes fruit and eventually can
 destroy the tree. There is no known cure.
 
 CANKER SUMMIT
 
 Now, experts from as far away as California, Spain, France, South
America
 and, curiously, Scotland, are at the canker summit, hoping to help
Florida
 cope with its crisis.
 
 Working in shirt sleeves amid a climate of urgency, they plan to emerge
 Thursday evening with a comprehensive list of research recommendations.
 
 Federal and state officials recently assembled $8 million to study the
 disease. The summit's recommendations could include a new emphasis on
 chemical and physical barriers to control canker's spread.
 
 Among the methods used in Brazil and Argentina, and under study here
this
 week:
 
 COPPER SPRAY
 
  Spraying trees with compounds containing copper and, sometimes, other
 chemicals. Growers in South America experienced substantial reductions
in
 canker lesions on fruit treated with the substances.
 ``Copper is highly effective for canker control,'' said Pete Timmer, a
 University of Florida researcher who has studied Argentina's program.
 
 The substance must be used carefully, though, because too much could
pollute
 the ground.
 
  Building windbreaks -- 300-foot-wide stands of silk oak, pine or other
 noncitrus trees -- on the fringes of citrus groves. These trees, immune
to
 the disease, can trap the bacteria and render it harmless before it
reaches
 citrus trees.
 
  New serums. Sprayed on trunks, leaves and fruit, they already have
been
 shown to activate and substantially improve trees' natural resistance
to
 other bacterial diseases.
 Tests on canker will start soon in Brazil and, possibly, Florida,
scientists
 said.
 
  Replacing highly susceptible varieties of citrus with more resistant
 ``cultivars.'' Brazilian researchers have found several resistant forms
of
 citrus, including the Valencia orange.
 Comprehensive programs using these methods have replaced most tree
 destruction projects in Brazil and Argentina, according to scientists
from
 those countries, though some heavily infested groves still must be
 destroyed.
 
 One problem for Florida growers: The cost of sprays, equipment and
fruit
 lost to canker can be high, raising production prices by hundreds of
dollars
 per acre and possibly making Florida citrus less competitive in world
 markets.
 
 Another: The leaf miner, an insect prevalent in South Florida, works in
 concert with canker to amplify the damage and complicate control
efforts.
 Wounds caused by leaf miners heal very slowly, allowing canker to
penetrate
 the tree with particular ease, Brazilian scientists said.
 
 Meyer said an official policy of living with canker in Florida rather
than
 ripping out trees is still months or even years away. Among other
things,
 environmental concerns about the use of certain chemicals could delay
 matters.
 
 But if ultimately adopted, the policy would save many South Florida
trees --
 and avoid widespread anger and heartbreak.
 
 Stephen Davis, a resident of Hollywood Hills in central Broward, said
two
 orange trees in his yard were recently marked for destruction. Both are
 healthy but apparently stand within 1,900 feet of an infected tree.
 
 ``It's going to be a terrible loss,'' he said. ``We enjoy the fruit and
the
 shade and the animals that are attracted by the trees.''
 
 A chemistry professor at Broward Community College, Davis fears that
the
 wholesale removal of citrus trees -- many of them healthy -- eliminates
some
 of the most hardy and resistant citrus.
 
 At last count, eradication crews have destroyed 431,516 trees in
Miami-Dade
 and 28,791 in Broward. Nearly all three million citrus trees in South
 Florida could be cut down.
 
 Residents believe their trees are being sacrificed to protect Central
 Florida's groves.
 
 Unfortunately, the return of summer rain and the hurricane season could
 hasten canker's advance. The highly contagious bacteria spreads easily,
most
 often hitching rides on wind-blown rain.
 
 ``We're getting into perfect weather for canker,'' said Mike Hunt, vice
 president of Brooks Tropical Farms of south Miami-Dade, Florida's
largest
 lime producer. ``If it becomes very widespread in the state, they will
have
 to give up on eradication and let everybody take their chances with
 management.
 
 ``Tell you the truth, it's something we'd like to try.''

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