Posts Tagged: Huanglongbing
The incurable citrus tree disease huanglongbing, or HLB, has been detected in Los Angeles and Orange counties and most recently in Riverside. The citrus disease is spread from tree to tree by Asian citrus psyllids, the insects that move the bacteria that cause huanglongbing.
Citrus trees infected with huanglongbing develop mottled leaves and produce fruit that is misshapen, stays green and tastes bitter. There is no known treatment for the disease, which usually kills the tree within three to five years, according to UC Cooperative Extension specialist Beth Grafton-Cardwell.
You can help prevent this disease from destroying California's citrus as well as your own trees.
Look for yellowed leaves on citrus trees. Nutritional deficiencies can also cause citrus trees to have yellow leaves so it is important to know the difference. Nutrient deficiency causes a similar pattern of yellowing on both sides of the leaf. HLB causes blotchy yellow mottling and is not the same on both sides of the leaf.
To identify the Asian citrus psyllid and the disease symptoms of HLB, see the fact sheets, videos in English and Spanish and other resources at http://ucanr.edu/acp.
If you see any trees that display symptoms of huanglongbing, contact your local agriculture commissioner.
To learn about the latest research, visit UC ANR's new Science for Citrus Health website at http://ucanr.edu/sites/scienceforcitrushealth.
More resources on Asian citrus psyllids and huanglongbing:
- ACP/HLB Distribution and Management http://ucanr.edu/acp
- UC IPM Pest Note http://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html
- Newest Detection of Citrus Greening (HLB) is in Riverside //ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=24776
- UC has boots on the ground in an unrelenting search for Asian citrus psyllid //ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=24752
- Detecting Asian citrus psyllid video https://www.youtube.com/watch?v=QhQXL4bwnXI
California citrus farmers have their ears perked for all news related to Asian citrus psyllid (ACP) and huanglongbing (HLB) disease, but the very latest advances have been available only in highly technical research journals, often by subscription only.
UC Cooperative Extension scientists are now translating the high science into readable summaries and posting them on a new website called Science for Citrus Health to inform farmers, the media and interested members of the public.
“The future of the California citrus depends on scientists finding a solution to this pest and disease before they destroy the industry,” said Beth Grafton-Cardwell, UC Cooperative Extension citrus entomology specialist. “Our farmers want to stay on top of all the efforts to stop this threat.”
Grafton-Cardwell and UC Cooperative Extension biotechnology specialist Peggy Lemaux are the two scientists behind the new website. When scientists make progress toward their goals, Grafton-Cardwell and Lemaux craft one-page summaries with graphics and pictures to provide readers with the basics.
For example, the website outlines scientific endeavors aimed at stopping the spread of huanglongbing disease by eliminating the psyllid's ability to transfer the bacterial infection. This section is titled NuPsyllid, and contains summaries of three research papers including one by UC Davis plant pathologist Bryce Falk.
Falk is collecting viruses found in Asian citrus psyllid; so far he has identified five. He is looking into the potential to utilize one of the viruses as is or modify one of the viruses to block the psyllid's ability to transmit the bacterium. For example, the virus might out compete the bacterium in the psyllid's body.
Another focus of the website is HLB early detection techniques (EDTs). If HLB-infected trees are found and destroyed before they show symptoms, ACP is less likely to spread the disease to other trees. EDT research described on the website includes efforts to detect subtle changes in the tree that take place soon after infection, such as alterations in the scents that waft from the tree (studied by UC Davis engineer Cristina Davis), changes in the proteins in the tree (studied by UC Davis food scientist Carolyn Slupsky) and starch accumulation in the leaves (studied by UC farm advisor Ali Pourreza).
As more research is published, more one-page descriptions will be added to the website. The website contains a feedback form to comment on the science and the summaries.
UC Lindcove Research and Extension Center. That brings to 29 the number of locations in the central San Joaquin Valley, from Bakersfield to Dinuba, where Asian citrus psyllids have been trapped.
Perhaps still more unsettling is the fact that reproducing populations of ACP have been found in urban areas in Tulare County, confirming that the pest is established in a county where farmers produce citrus valued at more than $1 billion annually.
“The psyllid is here, it's established, but still at low levels,” said Beth Grafton-Cardwell, director of the Lindcove REC and UC Cooperative Extension citrus entomology specialist. “We need to be very aggressive and treat it and eliminate populations as best we can.”
Asian citrus psyllids are a serious concern for California citrus producers because they spread Huanglongbing (HLB) disease. The disease causes tree decline, production of small, bitter fruit and eventually tree death. There is no cure once a tree is infected.
Around the world, once ACP arrives, HLB soon follows. Such was the case in Florida. ACP was first found in 1998, the disease followed in 2005, and by 2008 it had spread throughout the state.
“They allowed the psyllid and the disease to spread on nursery plants,” Grafton-Cardwell said. “Here, it's a different situation. We are taking many measures to reduce psyllid populations and limit their spread around the state in order to buy researchers time to find long-term solutions for HLB disease."
To date, only one HLB-infected tree has been found in California, a multi-grafted backyard tree in Hacienda Heights. It was quickly removed and destroyed. Other trees may be infected, but not yet detected. It will take a tree with HLB about a year to show visual symptoms of the disease. One goal of UC research is to identify a way to detect HLB more rapidly.
For example, scientists at UC Davis are refining a mobile chemical sensor that can detect diseased citrus trees by sniffing their volatile organic compounds. Another team of scientists is looking for changes in citrus trees' metabolism when infected with HLB.
Citrus growers can help by regularly monitoring their trees for signs of ACP and, when treating for other pests, use insecticides that are known to be effective against ACP. A chart of effective pesticides is on the interactive Asian Citrus Psyllid Distribution and Management website.
The website also contains information for residents who have citrus trees in their landscapes. Photos of the adult and juvenile insects, the distinctive waxy tubules left behind when they feed, and citrus leaves from and HLB-infected tree can aid in determining whether home trees are infested.
An initiative to manage endemic and invasive pests and diseases is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.
Ants can be a huge nuisance in and outside our homes, particularly if you have food lying around. But now, it turns out, they’re unwelcome, too, on citrus trees.
A year ago, UC Riverside entomologists released Tamarixia, a parasitoid wasp and natural enemy of the Asian citrus psyllid (ACP) imported from Pakistan, into a biocontrol grove in Riverside, Calif. Tamarixia can serve as an excellent biocontrol agent against ACP, a citrus pest first detected in 2008 in Southern California that is capable of spreading citrus greening disease, or Huanglongbing.
Female Tamarixia can kill psyllids also by “host-feeding.” They use their ovipositors as daggers to stab psyllid nymphs numerous times until the nymphs start to bleed. As bodily fluids ooze out of the nymph, Tamarixia sucks up this rich protein needed for developing more eggs.
An excellent way then to control ACP populations! Yes, but only until the ants come marching in. Argentine ants are threatening to disrupt the biocontrol of ACP by battling it out with Tamarixia on citrus branches. While not quite a Vader-Skywalker lightsaber duel on a precarious walkway, an “invasive meltdown” begins when the ants gang up to protect the nymphs.
“ACP nymphs produce a white, sugary waste product called honeydew, a good carbohydrate source for the ants,” explains Mark Hoddle, the director of the Center for Invasive Species Research at UC Riverside, whose research team has released Tamarixia into several Southern California citrus groves. “The ants, therefore, will protect the nymphs from Tamarixia. We have seen ants chase female Tamarixia off the psyllids, and even catch and eat them!”
“If you kill off the ants, Tamarixia can play the role of the biocontrol agent it was cast to do on citrus trees,” Hoddle says. “We’re seeing that the ants are impacting Tamarixia in two ways: they are preventing Tamarixia’s establishment in some areas; and, where Tamarixia is already established, the ants are not allowing these parasitoids to reach their full biocontrol potential.”