August 7, 2020
California's first-ever discovery in a commercial citrus grove of an infected Asian citrus psyllid (ACP) was made earlier this week.
The single ACP taken from a Riverside County citrus grove tested positive for the Candidatus Liberibacter asiaticus (CLas) bacterium, the pathogen responsible for Huanglongbing disease in citrus. This sets in motion several steps the state and Riverside County agricultural officials will take to protect the state's multi-billion dollar citrus industry. Most importantly, this will include targeted testing of plant material from the citrus grove in question for signs of the disease.
"This does not trigger a quarantine at this point," said Ruben Arroyo, Riverside County agricultural commissioner.
Even so, Arroyo says his office will coordinate with the California Department of Food and Agriculture on outreach to commercial growers and nurseries in the area over concerns related to the disease, and what people can do in response to the latest announcement.
The state will contact all growers within 250 meters of the find to recommend they apply aproved insecticides to all host plant material. This treatment recommendation is not mandatory.
"It's an eye-opener for us because this is the first time we've found an infected psyllid in commercial citrus," Arroyo continued.
The ACP is a tiny insect that is known to vector the bacterium that causes HLB in citrus trees. There is no cure for the deadly disease, which eventually causes development of misshapen and bitter fruit. For California's fresh-fruit industry, this could be a death-sentence as the fruit then becomes unmarketable.
Arroyo says the find was part of typical sampling efforts by the CDFA, based on existing work that focuses on "hot spots" where known psyllid populations exist and the likelihood is high that the insects could be carrying the CLas bacterium.
Much like a human can contract malaria through the "bite" (feeding activity) of a mosquito infected with the disease, so too is the pathogen causing the HLB plant disease transmitted to citrus. It happens through normal feeding activities of the insect on new plant growth. The concern is once an ACP has the bacterium; it can spread it to all the plants it feeds upon.
Monique Rivera, an Extension entomologist with the University of California, Riverside, says she will work with the grower to understand the psyllid, teaching the grower how to sample her trees for the psyllid, and the implications of good insect control in a region infested with the ACP.
California Citrus Mutual President Casey Creamer said the discovery should remind those in the industry to remain vigilant and do what citrus specialists recommend to protect their groves from the HLB disease. History illustrates the importance of managing psyllid populations as Florida's response to the insect 20 years ago was to largely ignore it. That inaction was followed by the rapid spread of the insect and disease which decimated Florida's citrus juice industry.
Creamer's understanding of where the infected psyllid was discovered left him somewhat assured because the region in Riverside County where the infected insect was discovered has limited acres of commercial citrus and therefore any potential spread of HLB to commercial citrus in California is limited with this find.
"I think we have the programs in place to protect the industry the best we can," he continued. "We just need to remain vigilant."
As of July 31, California has removed 1,974 residential citrus trees in four southern California counties after they tested positive for HLB. There are currently no known cases of HLB in commercial citrus in the state, which makes the latest find that much more troubling as it serves as a reminder to the industry about the importance of ACP control in their citrus groves.
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