Survey near UC-Lindcove to determine tristeza spread.
Virus-infected trees removed last year.

Cecilia Parsons
Capital Press

In the heart of the San Joaquin Valley citrus belt is the University of California, Lindcove Research and Education Center - and that's the problem.

Lindcove is home of the Citrus Clonal Protection Program, which supplies disease-free budwood to citrus nurseries that propagate the trees used by the industry. Disease-free is the key here, because time and money spent to bring a citrus grove into production are wasted if the trees are infected with a disease.

This is the challenge Lindcove Director Beth Grafton-Cardwell is facing. Fifty trees infected with the citrus tristeza virus were identified and removed at the center last year. Four were in the foundation block where budwood for the industry is cut. The rest of the infected trees were in research blocks. Grafton-Cardwell deemed the infection level high enough to restrict release of budwood, which limits citrus nurseries' ability to propagate trees for growers to plant.

Now, action by the Tulare County Pest Control District may reverse spread of citrus tristeza virus. Grafton-Cardwell said the district board voted unanimously last week to begin a tree survey project this spring to determine the extent of citrus tristeza virus in citrus blocks within three miles of Lindcove.

"I'm really excited about this. We'll find out just how big the problem is," said Grafton-Cardwell.

Tristeza is a viral disease transmitted by aphids when they feed on new flush in the spring. It is known as one of the most serious diseases of citrus, causing production losses. The virus strains can be mild to severe, but even mild strains in some citrus varieties pose problems because they can be transmitted by insects to other varieties that are less resistant.

To protect California's citrus industry all citrus budwood entering the state must be quarantined and tested to see if they are virus free. Testing of commercial citrus trees in the district that includes Lindcove was halted in 1998 when the district board voted to opt out of the eradication program.

Grafton-Cardwell said a survey conducted in 1998 found an infection rate of .14 percent. A survey last year on trees within half mile of Lindcove found an infection rate of 1.2 percent.

"We knew that it had increased, but we need to know how much," said Grafton-Cardwell. Research blocks at Lindcove near adjacent commercial groves were hardest hit by the virus. Grafton-Cardwell, who served on a district sub-committee, which presented the testing proposal, said the board is not committed to tree removal, but the survey would let them know the cost of removal if it is deemed necessary. She said they might need several million dollars in funding over several years for eradication.

Consequences of ignoring the problem could be harsh. Grafton-Cardwell said the Lindcove screenhouse that protects citrus trees from insects cannot produce enough budwood for the industry and does not include all the varieties that are sought by nurseries. Loss of budwood from the foundation block of citrus would impact nurseries' ability to propagate trees for growers, especially some of the sought-after varieties like the Tango mandarin.

She also noted trees lost from research blocks compromise ongoing studies in pest management, water use and other citrus management practices.

MaryLou Polek, program manager at the Central California Tristeza Eradication Agency, said the survey would begin in March with the flush of new growth. Results should be known by June.

The agency tests citrus trees in four pest control districts in the San Joaquin Valley for strains of the virus. Districts assess growers to fund the surveys. The Tulare district also assesses growers to fund research.

- Friday, February 15, 2008

Cecilia Parsons is a staff writer based in Ducor. E-mail: cparsons@capitalpress.com

Source:
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