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California ‘last man standing’ in citrus disease fightCalifornia ‘last man standing’ in citrus disease fight

HLB has already brought significant losses to groves in Florida, Texas, China and Brazil.Work is under way on the release of a biocontrol for the citrus psyllid.Earwigs, nitrogen and irrigation.

Dennis Pollock 1

May 7, 2012

5 Min Read

Ted Batkin, a leader in the battle to keep a deadly disease from ravishing California’s $2 billion citrus industry, had some reassuring words for Jerry Halford, a Sultana citrus grower unsettled by the discovery of the first documented case of huanglongbing in the state.

“We’re going to beat it,” said Batkin, president of the Visalia-based California Citrus Research Board. “We have the tools to prevent us from getting into trouble.”

Batkin’s reassurance came just before he was to open a talk with growers in Tulare by stating, “We don’t have to be panicked.”

Batkin proceeded to talk of the irony that the disease that cropped up in Hacienda Heights in Southern California was likely the result of a gift of budwood as a traditional act of friendship in the Asian community.

Batkin was bullish on the industry’s survival prospects, despite the threat, saying, “We may be the last man standing,” thanks to steps taken to keep any outbreak of the disease in check.

But he is no Pollyanna and has been warning the industry for years about huanglongbing, HLB, a disease that destroys trees and has no cure. It has already brought significant losses to groves in Florida, Texas, China and Brazil. The Hacienda Heights find was the first in California, and the hope is that – unlike other regions – California has prepared well to keep the disease and the pests that spread it at bay.

HLB, also called citrus greening, is spread by the Asian citrus psyllid, a flea-sized insect that numbers in the millions in the Los Angeles Basin, but has not spread into commercial groves to the north.

“It’s like Mary’s little lamb,” Batkin said. “Wherever the psyllid goes, it’s followed by the bacteria. We knew it was here, and HLB was confirmed in California on March 30. ”

The culprit in the Hacienda Heights case involves a lemon-pomelo tree and a New Year’s “good luck gift” of an infected graft of pomelo, Batkin said. He said it is a tradition in the Asian community to give such gifts.

Now, he said, a 5 mile radius of the infected tree, 93 square miles, is under quarantine and trees can’t be moved from there. Citrus trees valued at $75,000 in that area will be destroyed.

The infected tree was removed and cut up for further inspection. It had 21 different bud grafts, Batkin said.

Unforbidden fruits

Batkin said a program called “unforbidden fruits” is aimed at responding to the quest for illegal budwood from a foreign source by “getting those varieties everybody wants, bringing them in and cleaning up through the clonal protection program.”

Batkin appeared at the Tulare program while taking a brief time out from a three-day international conference in Visalia that drew scientists from the United States, Mexico and Belize.

He talked of research on odor-based lures and repellents for the psyllid and said work is already under way on the release of a biocontrol for the psyllid, the Tamarixia radiata. The predator is being mass produced in Riverside and it will be released at a rate of 200 to 400 per week.

“We want 5,000 to 10,000 a week,” Batkin said, pointing out there is greater acceptance by urban residents of insect control when compared with spraying of backyard trees.

Another weapon in the fight against the disease is a machine that “sniffs out” diseases and pests, Batkin said. It’s about the size of a loaf of bread and can sample trees at a rate of two per minute. In addition to looking for HLB, it can detect other diseases including various strains of tristeza and pests that include red scale.

Batkin’s concluding words: “Plant, plant, plant. We have the technology to keep you viable.”

Also on the agenda for the spring citrus meeting were these topics:

• A look at earwigs and the degree to which they are a pest or beneficial.

The European earwig feeds on both plant and animal material and regulates pest populations in orchards such as aphids, scale insects and mites.

But they also feed on citrus leaves and fruit, said Beth Grafton-Cardwell, an Extension specialist and research entomologist with the University of California at Riverside.

When spraying for the earwig, she said, it’s important to know where it will be, that it is likely on the ground in the winter and moves into trees in early spring.

Earwigs can be pests of leaves in young trees in the spring when they build up in wraps, and they can be pests of mature trees if they feed on new fruit at petal fall. But they can be natural enemies of citrus pests such as California red scale and researchers did not find them damaging citrus flush or fruit in the summer.

Tree wraps can be a refuge for the earwig and should be removed or an insecticide should be sprayed into the wraps and/or on foliage, Grafton-Cardwell said. Effective sprays include Lorsban, Sevin, Baythroid and Seduce.

Nitrogen management

• Nitrogen management in citrus under low volume irrigation, a topic certain to attract more interest because of environmental concerns about nitrates from crop land.

Mary Lu Arpaia, with the UC Kearney Research and Extension Center, talked of a study of leaching losses of nitrogen and the impact on fruit quality in relation to total applied nitrogen.

Foliar application of nitrogen resulted in lower groundwater levels of nitrates than soil application. Maximum yield and lower soil nitrate can be achieved using a combination of foliar and soil applied nitrogen, Arpaia said.

Maximum yield was attained with one to 1.5 pounds of nitrogen per year per tree. Peel thickness increases and peel firmness decreases with increased application of nitrogen.

• Partial root zone drying compared with conventional irrigation in citrus.

Carol Lovatt, professor of plant physiology and plant physiologist at UC Riverside, talked of research on cutbacks in irrigation and impacts on the bottom line – and fruit size – for growers.

She explained that partial root zone drying meant using two irrigation lines on opposite sides of a tree, alternating periods of irrigation so that one side was wet, the other dry.

That approach had been touted Australia years ago, but Lovatt and other researchers found that cutting irrigation in that way – and reducing conventional irrigation – by as little as 20 percent cut yield in citrus and resulted in smaller fruit.

“The real hit was on fruit size,” she said.

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