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Can guava help rescue citrus?

Published December 17, 2006


ORLANDO - Researchers will study whether placing guava trees in orange and grapefruit groves can protect the citrus crop from a devastating disease called greening.

The technique has been used in Vietnam with dramatic results, deterring both the insects that spread greening and the bacterial disease itself, according to top researchers at a federal laboratory in Fort Pierce.

The U.S. Department of Agriculture has within the past week bought or ordered every guava plant it can find - 15,000 to 20,000 so far - with plans to quickly establish field tests in South Florida.

"We're not saying this is the silver bullet, but this shows significant potential," said Calvin Arnold, director of the USDA's Horticultural Research Laboratory.

Vietnam has little citrus, but some small plantings there have survived at least 15 years despite the presence of greening - and preliminary tests hint that it is a protective effect from "volatile compounds" given off by guava, said Tim Gottwald, a plant pathologist who learned about the technique during a recent meeting in Japan.

Greening was first confirmed in Florida in 2005 but since then has been found in 13 South Florida counties - and the psyllid insect that spreads it is common throughout the state, giving the research extra urgency.

The disease is difficult to detect, ruins fruit and eventually kills trees.

Insect specialist David Hall of the USDA said the preliminary evidence seems to show that guavas suppress the levels of other insects that damage citrus such as aphids and leaf miners, which contribute to the spread of canker.

Oviedo Citrus grower Rex Clonts said Friday he was unfamiliar with the guava initiative, but expressed hope that it holds the potential for relief.

"It's such a devastating disease. It's got us all scared to death," Clonts told the Orlando Sentinel.

Guavas emit numerous compounds, and part of the Florida research will be to see if researchers can isolate which ones may be producing the deterrent effect.

[Last modified December 17, 2006, 00:44:23]

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