Over 200 people from the citrus industry and University of California (UC) Riverside gathered on Jan. 29 for Citrus Day. Growers and scientists alike were informed about the current status of huanglongbing (HLB) disease and the tiny insect that spreads it, the Asian citrus psyllid (ACP). The consensus of the speakers was that while HLB is a serious threat to California citrus, the defenses are holding as scientists continue to seek better weapons.
Controls put in place in commercial citrus operations seem to be effective. Victoria Hornbaker, director of the citrus pest and disease prevention division of the California Department of Food and Agriculture (CDFA), told the crowd that ACP has been detected in 26 counties. However, tarping bulk citrus during transport and strict procedures for growing nursery stock, along with regional quarantines, have so far prevented HLB from becoming well established in commercial groves. Orange County, the epicenter for HLB in California, and Riverside, where HLB has also been detected, are both under quarantine. Eradication has also been effective in some areas — nine counties have had no ACP detections for two years.
Backyard citrus is another story. The majority of HLB infections are in residential citrus. The CDFA conducts a trapping program to detect the insects and determine their range, performs residential surveys for the insect and HLB, and treats backyard trees in infected areas with pesticides.
Growers learned that new treatments based on the citrus microbiome might soon put California citrus on the offensive. Carolyn Roper, an associate professor of plant pathology at UC Riverside, has been studying bacteria that are naturally part of the microbial flora living in and on citrus trees. She discovered that one of them, cladosporol, kills the bacteria (CLas) that causes HLB. She recently received permits for conducting trials of three cladosporol variants on CLas-positive trees in UC Riverside’s new citrus research facility.
The day concluded with an opportunity to taste and rate 29 new citrus varieties developed at UC Riverside, some of which are HLB-resistant, and a demonstration by dogs that can detect CLas-positive trees by scent.
Source: University of California
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