California citrus growers are on the lookout for a new disease threat to their orchards.
The U.S. Department of Agriculture has confirmed findings of citrus yellow vein clearing virus, or CYVCV. It was first detected in March in residential citrus in the city of Tulare during routine tree surveys by the California Department of Food and Agriculture. It represents the first discovery of the virus in the United States.
The virus has not been detected in commercial orchards, CDFA said.
“We’re still learning a lot about it,” said Imperial County farmer Mark McBroom, who chairs the state Citrus Pest and Disease Prevention Program.
CDFA describes the virus as “a disease of quarantine significance to the United States,” as it can lead to “significant economic losses” and “cause serious damage to most citrus species” by diminishing fruit marketability. It has also been reported in grapes, beans and weeds.
Before being found in Tulare, the disease was restricted to Pakistan, India, Iran, Turkey and China, where it is in nearly all citrus-producing areas, according to CDFA.
The virus is transmitted by aphids, including the green citrus aphid, cowpea aphid and melon or cotton aphid. The citrus whitefly also is a vector. Plants become infected as insects feed on the foliage.
The virus is so called because leaves of infected young lemon and sour orange trees show a water-soaked appearance and yellow, clear veins on their front side. The leaves may also display crinkling and warping.
Symptoms vary depending on citrus variety, viral strain and environmental conditions, especially temperature, according to CDFA. Some infected trees show irregular ringspots on leaves and mosaic-like patterns on the fruit. The virus can be asymptomatic in some cultivars.
In infected lemon and sour orange trees, CYVCV is less pronounced in the summer. In severe infection, the fruit is malformed, and trees die back.
Tulare County Agricultural Commissioner Tom Tucker said there are protocols for invasive pests and diseases. But with CYVCV being new to California and the U.S., federal and state officials have yet to determine an appropriate response.
Victoria Hornbaker, CDFA director of the Citrus Pest and Disease Prevention Division, said the department “continues to conduct intensive delimitation surveys to better understand the current presence and potential impacts of CYVCV.” This work will help CDFA and USDA develop “an appropriate regulatory approach,” she added.
Because the virus is spread by insects that are known to be present in California, McBroom said it “makes it much more challenging to get your arms around it,” as eradicating the vectors “would be next to impossible, if not impossible.”
What’s encouraging, he said, is that CYVCV doesn’t appear to be “as detrimental as HLB,” referring to huanglongbing, or citrus greening, which eventually kills the trees. With CYVCV, fruit from the infected residential trees remains edible and “doesn’t appear different”—at least in the early stages—even though their leaves display symptoms, McBroom said.
So far, no new quarantines have been triggered. It’s unclear how agricultural officials handled the infected trees.
Hornbaker said CDFA and USDA remain in “an information-gathering stage.” She noted the state has been surveying “the core area” around the detection site in Tulare County and will expand its survey activities to Fresno and Kings counties in the coming months to determine the extent of the virus.
Key citrus stakeholders—including growers, regulatory officials of citrus-producing states, industry representatives and residents of private property that CDFA has surveyed—have been informed about the virus detection, Hornbaker said.
In addition, USDA has informed Japan and Taiwan, both of which import California citrus fruit.
“Fruit is not a pathway for virus spread,” Hornbaker said, “and these countries have not expressed concerns.”
Matt Watkins, director of farm operations for Bee Sweet Citrus, a grower-packer-shipper in Fowler, said some of the known symptoms of the disease aren’t all that uncommon in citrus, making it hard to tell if an orchard has infected trees.
Hornbaker said the best mitigation measure is to control the known vectors that can carry the virus. Because the virus can also be transferred on contaminated tools and equipment, she urged growers to sanitize them in between jobs or when moving from grove to grove.
Tulare County fruit grower, packer and shipper Doug Phillips noted that because of HLB and other citrus diseases that are already here, the state for years has maintained a robust program to protect its $3.63 billion citrus industry.
Even though the Citrus Pest and Disease Prevention Program was created because of HLB, McBroom said the state started doing routine annual tree surveys years ago because of diseases such as tristeza and citrus canker.
With CYVCV added to the list of potential threats, McBroom said it’s a concern because it could affect how growers harvest, move and sell their fruit. Every new pest or disease that pops up, he added, could lead to a regulatory response and trade ramifications. He said that means “additional costs (and) hoops to jump through…that become that much more detrimental to being able to make a profit and stay in business.”