Florida growers know firsthand what cruel twists the story of huanglongbing (HLB), or citrus greening, can take. Since HLB was first reported in a South Florida grove in 2005, the bacterium that causes the disease, Candidatus Liberibacter asiaticus, has destroyed tens of thousands of acres of trees in Florida, says Andrew Meadows, spokesperson for Lakeland-based Florida Citrus Mutual.
“We are under the assumption that we are 100 percent infected if we have a mature tree that we’re picking from,” he says. The vector that spreads the bacterium, the Asian citrus psyllid (ACP), has found its way to California:
In 2012, HLB was found in Hacienda Heights.
In 2015, HLB was found in San Gabriel.
Individual counties across Southern California have fallen under quarantine for ACP since the psyllid’s first detection in 2008.
Now, California citrus growers – who control a 270,000-acre, $3.65 billion-a-year industry – are on alert. State agencies are working to educate citrus growers, from backyard gardeners to the state’s citrus industry, about the threat ACP poses to them.
There’s no cure for HLB, and because the bacterial disease is spread by an insect no larger than a grain of brown rice, the cause can go unnoticed until the damage is done. California agriculture officials and university researchers, as well as industry leaders, are urging prevention as the only treatment.
“It’s the number-one priority of the industry,” says Joel Nelsen, president of the Exeter-based California Citrus Mutual. “It’s right up there with water as our two priority issues.”
Scientists are working on a number of other possible solutions in their quest to find a cure for HLB, says Grafton-Cardwell:
At least three research groups are working on genetically modifying the psyllid.
Other researchers are investigating traditional breeding of plants that can tolerate the disease.
Still other research groups are attempting to genetically modify trees to resist HLB, using genes from citrus and even spinach plants.
Researchers are also investigating using a modified, mild form of citrus tristeza virus with genes to resist HLB, to transfer resistance to trees.
Much of the research is being done in Florida, where HLB has invaded nearly every grove, but the work also is relevant to California growers.
Nobody knows whether the HLB story for California citrus growers will be one of triumph or tragedy. The story may be different depending on location and the crop being grown, Grafton-Cardwell points out:
Lemons and mandarins grown along the coast may struggle the most because they flush continually and provide a place for the psyllid to lay eggs and local conditions don’t require growers to spray as often for other pests.
The San Joaquin Valley has cold winters and hot summers that help suppress the disease.
Orange growers have an advantage as these trees harden off in the summer, limiting places for the psyllids to lay eggs.
Growers who treat their groves for various pests likely will find greater success in fending off ACP.
“This area tends to treat for more pests, such as thrips, citricola scale and the Fuller rose beetle,” Grafton-Cardwell says, referring to the San Joaquin Valley. “Most of the insecticides they’re applying for other pests are psyllid-effective.”
Bayer offers a portfolio of insecticides that control current pests in California including Movento® and Sivanto®, as well as Admire® Pro and Baythroid® XL. This proven portfolio provides the foundation of season-long ACP control with multiple modes of action, application timings and methods to ensure crop quality and help California citrus growers stay ahead of HLB. Learn more.