Citrus risks unclear from virus ID'd in Tulare
Aug. 28—Another incurable disease threatens Kern County's $1.3 billion citrus industry, this time a virus discovered 34 years ago in Pakistan but never in the Western Hemisphere until its finding in March during routine testing on a residential property in Tulare.
Citrus Yellow Vein Clearing Virus has the potential to cause "significant economic losses to the industry" by stunting tree growth, cutting yields and causing malformed fruit, according to the California Department of Food and Agriculture.
Observers worry the virus may spread quickly because it is carried by common aphids, whiteflies and clippers or other farm equipment that has not been sanitized between work in different groves.
State and federal officials hope to come up with a strategy for containing the disease based on ongoing efforts by the CDFA to identify the virus' geographical reach. The work continues in Tulare after infections were found in different areas of the city; it's planned to continue in the coming months in Fresno and Kings counties.
How big a concern the virus presents California's citrus industry remains to be seen, partly because its spread has not been fully assessed.
The hope is it's not as worrisome as citrus greening disease, or Huanglongbing, or HLB, a devastating bacterial infection for which no commercial treatment exists. Its winged vector, the Asian citrus psyllid, has been found in the Central Valley but the disease itself has not been detected north of the Grapevine.
"I don't think it's going to be as bad" as HLB, said Greg Douhan, a citrus adviser with the University of California Cooperative Extension program in Tulare County. He noted growers in the area use pesticides that seem to control the virus' vectors.
He said the virus is easy to diagnose: A halo circle is visible when light on the leaf from an infected tree is viewed from below.
The CDFA has a longer description of how to spot the virus, which manifests differently by type of citrus, with some infected trees being asymptomatic. It says young lemon and sour orange trees sickened by the virus have a water-soaked appearance with yellow, clear veins on the front of wrinkled, warped leaves. It says other trees show irregular ring spots on leaves or produce fruit with mosaic-like patterns on fruit.
Chief Research Scientist Melinda Klein at the Citrus Research Board in Visalia expressed confidence budwood cleanliness protocols in the state would limit the virus' spread in nurseries. She was more concerned with farmworkers' habits with regard to using bleach or other sanitizing agents on clippers and hedgers between jobs and orchards.
"If this is something we can contain and clear out, that would be great," she said. "We don't want to see another kind of virus like this."
Kern County Agricultural Commissioner Glenn Fankhauser said his understanding is that the virus was found on a ranchette-style property on a relatively small piece of land in Tulare. He said his concern is the disease could spread easily because of how common its vectors are in the state.
After its discovery in 1988 in Pakistan, the disease was found in 1997 in India, three years later in Turken and then, in 2009, in Yunnan, China.
Leading importers of California citrus, Japan and Taiwan, have been informed of the detection in the Central Valley and "have not expressed concerns," Director Victoria Hornbaker of the CDFA's Citrus Pest and Disease Prevention Division said by email.
She noted other key stakeholders including state regulators have been informed about the virus' detection in Tulare. Ongoing surveys will inform a cooperative response plan and regulatory approach, Hornbaker added.
The potential impact to commercial growers in the state, she added, is "yet to be determined."
