Citrus greening in leaves

Asymmetrical yellowing on citrus leaves can be symptomatic of citrus greening, or Huanglongbing. This kind of yellowing is different from the symmetrical yellowing that can be indicative of zinc deficiencies in the tree.

Could researchers have HLB cure in sight?

Could researchers be close to cure for citrus greening?    

With little to no hope of halting the advancement of the Asian citrus psyllid (ACP), researchers have pinned their goals on curing the deadly tree disease the tiny invasive pest spreads.

University of Florida researchers could be on the leading edge of stopping Huanglongbing (HLB) in citrus, according to the California Department of Food and Agriculture. Scientists caution such a cure remains years down the road for commercial growers.

A chemical used to treat gout in humans is showing promise in the fight against citrus greening, or HLB. Benzbromarone was sprayed on greenhouse citrus shoots and was shown to be 80 percent effective in combatting the disease in research trials.

Researchers published their findings in the journal PLOS Pathogens.

A team from the University of Florida’s Institute of Food and Agricultural Sciences discovered the chemical that appears to kill HLB. One possible difficulty in gaining U.S. approval for this chemical is that its use to treat gout has been linked to acute liver injury in humans. The chemical has thus never been approved for use in the United States.

Citrus greening quickly spread through Florida citrus groves after growers there largely ignored the Asian citrus psyllid when it was first discovered in 1998. The pest quickly spread throughout the state and across the southern United States.

The pest was discovered in California residential citrus in 2008. One tree in urban Los Angeles later tested positive for HLB.

Yellowing can be zinc problem

The ACP is a phloem feeder, according to Mark Hoddle, a biological control specialist with the University of California, Riverside. This process of feeding on the life stream of the citrus tree allows the pest to spread the bacteria much like a mosquito spreads malaria in humans.

The bacteria limits the movement of phloem in citrus trees, causing symptoms that can appear like zinc deficiency with the yellowing of leaves. The key difference is that HLB symptoms reveal themselves in asymmetrical yellow blotching, while zinc deficiencies are symmetrical in citrus leaves. Other HLB symptoms appear in fruit, eventually making it too bitter to consume.

According to the U.S. Department of Agriculture there are 56 host plants for the ACP. The pest favors citrus plants and citrus relatives, including lemon, lime, tangerine, mandarin, grapefruit, kumquat and orange jasmine.

The ACP is established in southern California and has been found in California as far north as Fresno County. Quarantines regulating the shipment of fruit are established in California’s main commercial citrus region in Fresno, Tulare and Kern counties, and throughout southern California.

 

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