A tell-tale sign of spring in California is a flush of new leaf growth on citrus trees. Because the feathery light green leaves are particularly attractive to Asian citrus psyllids (ACP), the leaves' emergence marks a critical time to determine whether the pest has infested trees.
“We encourage home citrus growers and farmers to go out with a magnifying glass or hand lens and look closely at the new growth,” said Beth Grafton-Cardwell, UC Agriculture and Natural Resources (UC ANR) citrus entomologist. “Look for the various stages of the psyllid – small yellow eggs, sesame-seed sized yellow ACP young with curly white tubules, or aphid-like adults that perch with their hind quarters angled up.”
Pictures of the Asian citrus psyllids and its life stages are on the UC ANR website at http://ucanr.edu/acp. If you find signs of the insect, call the California Food and Agriculture (CDFA) Exotic Pest Hotline at (800) 491-1899.
Asian citrus psyllids are feared because they can spread huanglongbing (HLB) disease, an incurable condition that first causes yellow mottling on the leaves and later sour, misshapen fruit before killing the tree. ACP, native of Pakistan, Afghanistan and other tropical and subtropics regions of Asian, was first detected in California in 2008. Everywhere Asian citrus psyllids have appeared – including Florida and Texas – the pests have found and spread the disease. A few HLB-infected trees have been located in urban Los Angeles County. They were quickly removed by CDFA officials.
“In California, we are working hard to keep the population of ACP as low as possible until researchers can find a cure for the disease,” Grafton-Cardwell said. “We need the help of citrus farmers and home gardeners.”
Grafton-Cardwell has spearheaded the development of the UC ANR ACP website for citrus growers and citrus homeowners that provides help in finding the pest and what to do next. The site has an interactive map tool to locate residences and farms that are in areas where the psyllid has already become established, and areas where they are posing a risk to the citrus industry and must be aggressively treated by county officials.
The website outlines biological control efforts that are underway, and directions for insecticidal control, if it is needed. An online calculator on the website allows farmers and homeowners to determine their potential costs for using insecticides.
There are additional measures that can be taken to support the fight against ACP and HLB in California.
When planting new citrus trees, only purchase the trees from reputable nurseries. Do not accept tree cuttings or budwood from friends or relatives.
After pruning or cutting down a citrus tree, dry out the green waste or double bag it to make sure that live psyllids won't ride into another region on the foliage.
Control ants in and near citrus trees with bait stations. Scientists have released natural enemies of ACP in Southern California to help keep the pest in check. However, ants will protect ACP from the natural enemies. Ants favor the presence of ACP because the psyllid produces honeydew, a food source for ants.
Two additional trees in San Gabriel have tested positive for Huanglongbing. The two trees, an orange and a kumquat, are on separate properties but are both within the core area in San Gabriel where 10 diseased trees were confirmed last summer. Given the close proximity, there will not be a quarantine expansion.
One of the HLB-positive trees has already been removed and California Department of Food and Agriculture officials are in the process of contacting the other homeowner to schedule tree removal. Agriculture officials are working quickly in the area.
Citrus trees in San Gabriel had already been treated for the Asian citrus psyllid within the last few weeks as part of CDFA's routine HLB response. Asian citrus psyllid populations are closely monitored in areas where HLB has been detected and treatments occur if there is a noted increase in population size. Since trees have been recently protected, no additional treatments will take place at this time. Instead, CDFA will focus on sampling extensively in the area. Much of the area has already been sampled and CDFA's lab has identified all samples from San Gabriel as high priority.
The Citrus Pest & Disease Prevention Program is working with the Los Angeles County Agricultural Commissioner's office and CDFA to develop a multi-lingual informational flier to notify residents of the significance of these finds and potential implications to other citrus trees in the area. CDFA staff will distribute this information as they go door-to-door sampling and surveying.
More information will be shared as it is available. In the meantime, the citrus industry is encouraged to keep a critical eye on all plant material moving into or out of your groves. Remove all leaves and stems, shake out picking bags, inspect harvesting equipment and educate fieldworkers. Additionally, get on board with area-wide treatments. Collectively, as a team, we can all save our citrus trees.
Residents in the area who think they may have seen ACP or symptoms of HLB on their trees are urged to call CDFA's Pest Hotline at 1-800-491-1899 or your local agricultural commissioner's office.
Well it came again, the Citrus Tasting at Lindcove Research and Education Center in Lemon Grove near Exeter, close to Visalia and just down the road from Fresno and up from Tulare. They came, growers to see and taste new and old varieties. And then the next day, the general public with oooos and ahhhs to taste the range of flavors we call citrus. Big fruited pummelos and little fruited finger limes. Sweet, sour, not sweet, not sour, dull, and boing!. Growers came on Friday morning and the general public the following Saturday. It was crowded both days.
Citrus is wonderful, everyone knows, but it is also under dire threat of Huanglongbing and the potential destruction of this industry and the trees that are found in many backyards. So in a completely unscientific survey, I asked growers why they were there if their world was about to end. First of all, those who showed up were already optimistic about the future, so there was already a self-selection. But, growers felt like a solution would be found, science would find an answer. Driving across the Valley and through coastal counties like Ventura there are lots of new plantings......if there's water. But it's surprising how confident growers are about finding a solution. There are some hopeful signs out there like the new rootstock release from USDA of US-1516 which shows a lot of tolerance to the disease. Then there is the potential of disease tolerance in a citrus produced in Florida from a collaboration of Southern Gardens, USDA and a consortium of Universities. Yes, there is hope, but years are still needed to test and gear up for production for commercial applications.
So it was good to be around growers who have an enthusiasm for the future and looking for new planting varieites.
And they are both grapefruit, one is Melogold the one on right is Oro Blanco
Buddha's Hand citron
The Citrus Display at Lindcove Research and Extension Center, before the crowds
There is some variability in citrus susceptibility to both the psyllid (Westbrook et al and Hall et al) and the bacterial infection (Shokrollah et al and Stover and Mc Collum). It is not fully clear at this point which of these species would be best to include in a breeding program, but both scions (http://www.concitver.com/3erEIIC2011/Viernes_23_sep/Ed_Stover/Ed_Stover.pdf) and rootstocks (http://www.flcitrusmutual.com/files/4cbb1e3c-1e1f-4b04-a.pdf) are being evaluated.
Some varieties like Australian Finger Lime (Microcitrus australasica) might show more resistance/tolerance to HLB than other species. At the UC Citrus Variety Collection website, it's possible to see the wide range of citrus species that are available for breeding and the commercial availability of those species. The collection is a view into the different materials that breeders can select from, in order to improve resistance to this citrus disease.
In a landmark step in the fight against citrus greening disease, also known as huanglongbing (HLB), the U.S. Environmental Protection Agency has approved an application from Southern Gardens Citrus of Florida for an Experimental Use Permit under the Federal Insecticide, Fungicide and Rodenticide Act. This allows researchers to move forward in the development of the possible use of a spinach protein to help control this devastating disease.
Ricke Kress, president of Southern Gardens, said this latest development is a milestone in efforts to fight off HLB.
“A final solution to eliminating this disease may still take some years,” Kress said, “but the latest EPA action and continuation of all research projects are major steps in the right direction.”
Research conducted by Dr. Erik Mirkov, a plant pathologist at the Texas A&M AgriLife Research and Extension Center at Weslaco, resulted in the production of proteins that appear to provide effective control of citrus greening disease.
“Citrus greening is a bacterial disease that affects the vascular system of the tree,” Dr. Mirkov said. “It basically shuts off the tree's ability to take up and use water and nutrients, causing the tree to die. We were able to improve the transgenic trees by having the genes express themselves in the vascular system.”
HLB is the most serious citrus disease in the world. It was first identified and confirmed in Florida in 2005. HLB is now found in every Florida county where citrus is grown commercially. There are no successful control programs yet available for this disease. (NOTE – HLB has been detected just once in California, at a residential property in Los Angeles County in 2012)
Consistent with the conditions established by EPA, researchers may now move forward with field tests to evaluate the efficacy of the spinach protein against HLB in citrus plant tissues and continue generating the environmental, health and safety data that are required under federal law to support a fully registered product for commercial use.