Planet Earth

Steamy Solutions to Citrus Sickness

From tarps to steam machines, more heat could save the nation's orange and grapefruit trees.

By Sarah WebbSep 4, 2018 4:48 PM
How It Works1. A tarp completely envelops the tree 2. Machine blasts 140-degree steam for 30 seconds, then the tarp is lifted. 3. The steamed tree is now protected from bacteria. | University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center


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A steam heat treatment machine at work. | Mariuszblach/Thinkstock

Since 2005, the bacterium Candidatus liberibacter, spread by Asian psyllid bugs, has ravaged orange and grapefruit trees in Texas, California and Florida, producing splotchy leaves and misshapen fruit. Agricultural engineer Reza Ehsani of the University of Florida helped come up with the only available treatment: heat.

Tiny Asian psyllid bugs (right) are responsible for spreading bacteria that harm U.S. citrus trees (left). | University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center (2)

Heating orange trees to a consistent temperature of about 108 degrees Fahrenheit for up to 90 seconds significantly reduces the number of bacteria without harming the fruit or creating any other experimental hazards. Ehsani’s initial studies started simply, with translucent tarps thrown over individual trees to trap the heat from the sun. The treated trees improved dramatically — some even returned to 100 percent productivity — and desperate growers are already trying the technique, even though the trees remain vulnerable to reinfection.

But this individual approach is effective only in groves with few infected trees. In Florida, with widespread disease now endangering nearly 70 million trees (which provide 80 percent of America’s orange and grapefruit juice), single tarps won’t cut it. Ehsani and his colleagues recently debuted a prototype device that blasts trees with a 30-second shot of steam at 140 degrees; just one spritz is enough to keep a tree safe for at least a year or two. Companies are already working on commercial models, which will attach to tractors or other common equipment.

Though he’s working on improving the device, Ehsani acknowledges that heat treatment probably won’t provide a permanent solution — that’s likely the domain of chemical treatments years down the line. “But it buys us time, and that’s what we really need right now.”

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