The curse of the Yellow Dragon

This detective story will sound familiar to hazelnut growers in Oregon.

Published on September 28, 2017 8:16AM


The hunt has all the makings of a Sherlock Holmes detective story, complete with an exotic villain and a victim desperately in need of rescue.

At risk is U.S. citrus fruit production, worth $3.4 billion a year. Florida’s citrus production alone is worth $1 billion, according to the National Agricultural Statistics Service. As a whole, Florida’s entire citrus industry, including growers, processors and packers, generates $9 billion a year.

But something has been killing citrus trees in Florida. The number of orange trees has dropped 25 percent, from 80 million to 60 million, in the past nine years. The number of grapefruit trees has dropped 64 percent, from 14 million to 5 million, according to USDA.

Only a few years ago, Florida had nearly 1 million acres of citrus groves. Today, it has less than half that, 410,700 acres.

The villain is huanglongbing — Chinese for “yellow dragon disease.” Discovered nearly 100 years ago in China, the disease has been decimating the citrus industry around the globe. Since its discovery, the bacterial disease has killed more than 100 million citrus trees in 40 countries. Yellow dragon disease is also known as citrus greening and by the initials HLB.

There exists no cure for yellow dragon disease. It is spread by the Asian citrus psyllid, a tiny insect that sucks the sap of an infected tree and infects the next tree it visits. Yellow dragon disease first causes the leaves to turn yellow. Then the fruit turns greenish yellow and becomes unmarketable. Finally, within a few years, the tree dies.

Scientific detectives are using high-tech tools to gain an understanding of the yellow dragon and the psyllids that have spread it to 15 states or U.S. territories, including Florida and California, the nation’s largest citrus fruit producers.

At the University of Florida, Clemson University, Texas A&M University and the USDA Agricultural Research Service, scientists are undertaking a computerized search for varieties of citrus trees most resistant to the disease. They hope to use the information to breed varieties of trees resistant to yellow dragon disease.

This narrative will sound familiar to hazelnut growers in Oregon. Eastern filbert blight took hold in the hazelnut trees of Oregon’s Willamette Valley in the mid-1980s. The fungal disease spread through the valley despite farmers’ efforts to control it using fungicides and by pruning and removing infected trees.

Shawn Mehlenbacher, a Oregon State University hazelnut breeder, led the successful effort to study hazelnut trees from around the world and develop new varieties that are resistant to EFB.

His is one of the great success stories of OSU agricultural research.

“Without the Oregon Agricultural Experiment Station the hazelnut industry would disappear,” he said in a 2014 university video. “But because we have new resistant varieties it is expanding, not disappearing.”

Oregon’s hazelnut industry, which produces 99 percent of the nation’s crop, continues to expand. Today, Oregon farmers grow hazelnuts on 37,000 acres — and plant more EFB-resistant trees each year.

This success — the ability of scientific research to overcome a seemingly insurmountable problem — should be encouraging to citrus growers in Florida, California and elsewhere.

With adequate resources — hundreds of millions of dollars have already been funneled into research from the industry and the state and federal governments — scientists will be able to breed citrus trees resistant to huanglongbing. They will slay the yellow dragon forever.


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