The California Citrus Research Board (CRB) has mounted an aggressive, three-pronged campaign to repel the devastating citrus disease, Huanglongbing (HLB), and its vector, Asian citrus psyllid (ACP).
Once an HLB infection occurs in citrus or related plants, it progressively yellows foliage, damages fruit, and eventually causes death of the plant.
There is no cure for HLB, and the only recourse is removal and destruction of infected trees. It has caused losses in Florida and other Southern states, and it has long been a scourge of citrus in Asia. Lifespan of infected citrus orchards is reduced from the normal 50 years to 15 years.
The aphid-sized ACP has been found in Southern California, and quarantines on citrus movement are in effect in Imperial, Los Angeles, Orange, Riverside, and San Diego counties. It was also detected in airline baggage containing an adult and nine nymphs carrying HLB in Fresno. However, at this writing, no ACP infected with the disease have been found in plants.
The threat of HLB has prompted a major cooperative effort by federal, state, county, and pest control district agencies.
Mary Lou Polek, CRB vice president of operations, described the three elements of the board's campaign against the disease during a meeting of growers at Exeter.
A veteran plant pathologist with the California Department of Food and Agriculture and other assignments, she took the post last November after the California citrus industry voted additional research funds to support the program.
The program consists of field surveys and sampling, a diagnostic laboratory at Riverside to process data, and procedures to put to use the findings for the industry. A nucleus of three specialists is involved in the program with more personnel to be added as necessary.
“The purpose of our program,” Polek said, “is to augment the activities of CDFA and the county agricultural commissioners. Our focus will be on trapping for ACP in commercial citrus and areas around packinghouses.” CDFA will continue to monitor residential areas and nurseries.
“I want to emphasize,” she said, “that we know absolutely nothing about what this psyllid will do in California or how the disease will manifest itself here.”
They will use GSP-guided recording equipment to funnel trapping data into an interactive, Web-based program. Trees with sticky traps will be labeled by specific CRB bar codes and photographed so that any finds can be precisely recorded and located.
Traps will be monitored at two-week intervals. A pilot trapping program was done near the Salton Sea for training. The trapping will be done jointly with CDFA's glassy-winged sharpshooter program.
As an example of the depth of the program, when maps are completed it will show citrus species, variety, and rootstocks, along with when leaf flushing, which attracts ACP, will occur. Traps will also be placed along highway routes for citrus shipments.
Riverside is the location of the centerpiece of the program, the diagnostic laboratory which opened in late August. It was chosen because of the proximity of the University of California campus and biotechnology activities there.
Equipment for DNA and polymerase chain reaction analyses is state-of-the-art and capable of processing 96 samples in the time it takes for CDFA in Sacramento to handle 16.
Steps for USDA certification of the lab have begun, and it will be available for other CRB research projects. “The laboratory will be a bridge to move the research and technology out for practical use by growers,” Polek said. “All the remodeling of the building is done, all the equipment is installed, and we are optimizing our lab protocols with potato psyllid, which is very similar to Asian citrus psyllid. The lab is ready to roll.”
Polek added that the citrus industry can be assured that program personnel are out looking for HLB and when it is found, infected trees can be identified for removal.
Beth Grafton-Cardwell, Extension entomologist at the Kearney Agricultural Center, Parlier, said the telltale, early signs of HLB are yellowing of newly-flushed citrus foliage.
Since HLB can take years before its symptoms are visible, the first line of defense is inspection for and elimination of the highly-efficient ACP vector.
Noting that it took only three years for the ACP to become established throughout Florida, Grafton-Cardwell said authorities are trying to prevent the same from happening in California.
Already in the Southeastern U.S., Cuba, and Mexico, the insect, she explained, can readily be imported into California on plant hosts, unprocessed fruit, or cut flowers. There is also concern about it possibly entering through contraband citrus sold in flea markets.
Once HLB arrives in California, it could be distributed rapidly by the ACP through backyard host plants before moving on to commercial citrus. In that case, nurseries will have to place nursery stock in screen houses to keep it from the ACP, and some have already prepared structures.
She urged PCAs and growers to be on the alert and watch for ACP in new flushes of citrus growth. Materials with descriptions, photos, and guidance are available through CRB and local Cooperative Extension offices.
In addition to visual surveys, sticky traps and vacuuming can be used to collect specimens in high-risk locations such as groves and packinghouses. Educational seminars are planned throughout the state to support the monitoring.
Citrus in backyard sites where ACP is found will be treated with Merit and Tempo insecticides by CDFA to control adults and eggs. In quarantine areas, wholesale nurseries are treating host plants to reduce the risk of ACP moving from residential areas into retail plants.
“It also affects commercial citrus in those areas,” Grafton-Cardwell said, “by growers having to increase insecticide treatments from two or three a year to more like five to seven a year.” Even so, she added, insecticides never kill every individual pest.
Increased pressure from ACP will also negatively affect the citrus IPM program, she predicted, because the majority of the most effective insecticides are pyrethroids that will disrupt natural enemies of pests.
“It is very important at this time to keep the insect slowed down and as limited as possible,” Grafton-Cardwell said.
“This is so that we can delay the arrival of HLB as long as possible and give researchers time to respond with new insecticides for the insect and new plant types that can reject the disease.”