Dying Citrus Tree
The Asian Citrus Leaf Miner
Tree Disease Basics playlist
Whiteflies in Temp AZ
The world’s most insidious citrus disease invaded Florida in 2005, wreaking havoc on its iconic groves with stunning speed. After just a decade, virtually every citrus tree in the state was dying or infected.
Then in 2012, the disease — Huanglongbing, commonly known as citrus greening — was discovered in California. It showed up first in a Hacienda Heights backyard, on a pummelo branch derived from budwood that had been smuggled from China, where the disease is epidemic
The next infected tree wasn’t found until 2015, and for two years after that only 81 more turned up. In mid-2017, however, a new sampling method and improved detection technology led to the discovery of far more HLB-positive trees in California: 1,135 as of March 11.
Now researchers and farmers are racing to fend off the disease. This month, more than 500 scientists from around the world gathered in Riverside at the sixth International Research Conference on Huanglongbing, meeting in California for the first time. Their findings show that although the disease is spreading rapidly in the Southland and no breakthrough is imminent, a host of new detection methods and strategies could help California avert the kind of disaster that destroyed almost three quarters of Florida’s citrus production.
Huanglongbing originated in Asia a century or more ago. It is caused by a bacterium, Candidatus Liberibacter asiaticus, transmitted by a tiny insect, the Asian citrus psyllid, which feeds on young citrus leaves. HLB clogs citrus trees’ phloem, a vascular tissue that transports sugar from the leaves; this causes the most symptomatic fruit to become small and bitter, and eventually makes trees unproductive or kills them.
Until now California has avoided painful losses from HLB, but that may be changing.
“I would describe the current trend as exponential,” said Neil McRoberts, an associate professor of plant pathology at UC Davis.
The infected trees have been found mainly in Orange County, where Garden Grove and Santa Ana accounted for 702 detections, and in the San Gabriel Valley and adjacent regions of Los Angeles County. So far confirmed detections have all been in backyard trees, not commercial groves.
Agricultural authorities promptly cut down all the infected trees, but these may be only the tip of the iceberg because the standard HLB test can take many months or years to detect a new infection. During this time trees appear normal but can infect feeding psyllids, which in turn can spread the disease to other trees.
Scientists have labored for a decade to develop devices to detect the disease earlier, but recently a low-tech solution has proved more promising: dogs trained to sniff HLB-infected trees.
Trained dogs can actually smell the bacteria within a few weeks after infection, Tim Gottwald, a U.S. Department of Agriculture plant pathologist, said during a presentation at the Riverside conference. In Florida they’ve been 99% accurate, and in tests in December and February under challenging conditions (such as distractions from homeowners’ dogs) in Southern California backyards, they were right more than 92% of the time, he added.
If the canines are right, HLB may be more widespread than standard tests show. Two years ago, the dogs signaled infections in 72 trees at UC Riverside and in four trees in two commercial groves in Kern County. The trees continue to appear negative on molecular tests, but this method typically lags infection. Some California scientists maintain, and hope, that the dogs are wrong, perhaps because they’re smelling something else in the trees, but only time will tell.
Dog handler with an HLB-detecting dog used to find citrus trees infected with a bacterial disease threatening California citrus.(F1K9)
Detecting and removing infected trees is half the battle; controlling the insect vector is equally crucial. After the Asian citrus psyllid showed up in California in 2008, citrus growers started spraying to suppress it, and growers in psyllid quarantine areas are now required to do so to sell their fruit to packinghouses.
In urban areas, where systematic spraying is problematic, University of California scientists began in 2011 to release a natural enemy of the psyllid from Pakistan, a parasitic wasp named Tamarixia radiata, which has significantly reduced but not eliminated psyllid populations.
The Asian citrus psyllid continues to spread each year, and is now present in 28 California counties. It’s most abundant in the coastal and Inland Empire districts of Southern California, where citrus trees develop new leaves frequently, providing plentiful food for psyllids. In the San Joaquin Valley, the state’s leading citrus-growing area, and in the hot desert valleys, conditions are less favorable for psyllids, and growers have been able to suppress populations below detectable levels most of the year.
By DAVID KARP
MARCH 29, 2019
Along with the citrus problems we have known about for years there are at least two new threats to the health of your citrus trees please watch the videos on this page to learn more.
Arriving here in 2011 and breeding up to 15 times a year, the Asian Citrus Leaf Miner was in every citrus tree I looked at for several years.
The population grew unchecked well into the summer of 2019,. So for at least 8 years, the leaves on your citrus trees have been producing far less energy than normal.
Because of this the reserve cells are dangerously low. Biologically speaking, your citrus trees have run out of gas.
Because it has no natural predator in Arizona there was nothing to keep it in check. However now it competes with the Ash Whitefly.
It takes years but eventually a citrus trees reserves will be drained to the point that it can no longer defend itself against any insects or soil born fungus.
That’s where we come in, if it’s not too late we can get you started on a program to restore the energy reserves of your trees.
Watch the videos on this page to learn more