HLB threat continues in California citrus groves
SALINAS, Calif. — The devastation of Florida’s citrus industry from Huanglongbing (HLB) could become the future for California citrus – or not.
Tim Lewis, an inspector with the Monterey County Agricultural Commissioner’s Office, spoke about the citrus disease March 27 at a panel session at the Salinas Valley Ag Tech Summit in Salinas. The disease continues to threaten California’s, the nation’s and world’s citrus supplies.
Florida citrus production has dropped 70%, Lewis said, due to HLB, spread by the invasive Asian citrus psyllid. It kills trees after it causing off-tasting and malformed fruit. The insect, and the disease, were found in Florida in 1998 and travelled west, reaching California in 2008.
Although the disease hasn’t been found in commercial groves in California, the psyllids continue to spread, as do quarantine zones.
Citrus is among California’s 15 top commodities and worth $3.7 billion, or about 7.3% of the state’s $50 billion agriculture economy, according to Lewis. That production makes California the world’s No. 1 citrus producer.
The nation’s citrus industry has been researching the psyllid and the disease, and Lewis shared some of the newer information.
Two psyllids transmit HLB, but so far, only the Asian citrus psyllid has been found in the U.S., he said. Also, the bacteria-based disease has three forms — two forms survive in warmer climates and the third in cooler climates. That’s not good for California, he said.
“There’s not one (climate) that we can say, ‘Oh well, we can grow citrus here because it won’t be present,” Lewis said. “There’s one (bacteria) that will take (the climate) either way.”
So far, infected trees have been confirmed only in backyard citrus and not commercial orchards, Lewis said. He walked the audience through the insect and disease symptoms to watch for.
Psyllids feed on citrus trees’ new growth, and transmit HLB after feeding on an infected tree and moving to other trees. The deadly bacteria lives in a tree’s phloem, causing it to swell, and blocking it and the nutrients it carries from reaching the full tree, he explained. As a result, the ends of trees turn yellow, and leaves get mottled blotchy green within yellow.
But those symptoms take two to five years to be noticeable, Lewis said, and can be hard to distinguish from other issues such as iron or zinc deficiencies. That’s been a huge challenge, he added.
“It can keep on spreading for a couple of years before you realize you have a problem inside your orchard – that’s what happened in Florida,” he said.
Another problem is the psyllid’s prolific breeding.
One female psyllid can lay up to 800 eggs, have up to 10 generations a year and propagate year-round, Lewis said, although at smaller numbers during the winter. Psyllid eggs can become adults in 15 days in 75- to 80-degree temperatures.
“What does that mean for southern California when year-round they’re reaching those temps consistently?” Lewis asked. “It means that year-round, they’re having full bloom populations that are continually feeding as well as moving to new locations.”
Still another newer-learned problem is the large number of host trees to the psyllid. The entire rutaceae family of plants, which includes citrus trees and ornamentals such as flowering jasmine, is a host, Lewis said. The original belief was it was limited to citrus trees. By not quarantining other plants initially, a psyllid was able to travel into Texas from Florida on an orange jasmine tree, eventually leading to infestations.
In Florida, it took about 19 years for the industry’s near-ruination, with HLB-infected trees in 33 counties since the first confirmed psyllid find.
In California, the insects, first confirmed in Southern California in 2008, have spread as far north as Placer County. Nearly 1,120 trees have been confirmed with HLB so far in Los Angeles, Orange and Riverside counties, Lewis said.
Monterey County, where Salinas is located, has a citrus industry worth $4.4 billion, ranks fourth in the state, with 12,000 acres, Lewis said. The psyllid has been found but no HLB-infected trees.
The state and industry response includes quarantining the movement of host trees and nursery stock, trapping insects to track their movement, treating trees found with the insect with pesticides, breeding and releasing predatory insects and destroying HLB-infected trees. Recent news reports noted new detection tools include dogs trained to sniff out the disease.
“California learned a lot from what Florida went through, and we’ve been able to put things in place that are keeping that spread down,” Lewis said.