Ki‘ai Moku: Serious citrus disease perched on Hawaii’s doorstep
Tangerines, oranges, lemons, limes, pummelo and grapefruit – sharing a box of citrus just picked from the backyard is part of life in Hawaii, as much as leaving your slippers outside the front door.
But imagine walking outside to find your trees covered in bitter, misshapen fruit: no more fresh lemons, tangerines or oranges from your yard. Backyard gardeners and commercial growers across the Mainland are scrambling to protect their citrus in the face of one of the most serious citrus diseases in the world, a disease perched on Hawaii’s doorstep.
Citrus greening disease, also known as huanglongbing or yellow dragon disease, originated in Asia. It was first detected in the United States in Florida in August of 2005. By July 2008, it had spread across the state. It has since sprung up in backyards and farms throughout the Southern United States. Once infected, plants don’t recover and thousands of trees throughout the Southeast have died. The impacts to the citrus industry in Florida have been profound. California citrus growers are bracing themselves after the disease popped up in a Los Angeles suburb last summer.
A tiny, gnat-sized insect, the Asian citrus psyllid (Diaphorina citri), is responsible for spreading citrus greening disease. These psyllids feed on the stems and leaves of citrus and must feed on an infected tree to spread the bacterial disease. Currently, citrus greening is not present in Hawaii, but we do have sizeable populations of non-native Asian psyllid. Across the Mainland the trend has been for the arrival of the psyllid to be followed by the disease.
The Asian citrus psyllid was first detected on the Big Island in 2006. Monica Tauyan is a plant pest control technician with the Hawaii Department of Agriculture. She is part of a team that regularly surveys citrus across the state for citrus greening. Tauyan has no problem finding the Asian psyllid living on a variety of different citrus.
“The psyllid causes leaf curl,” she said. “But the major concern is the disease.” If citrus greening arrives, the psyllids will carry the disease from tree to tree. Tauyan conducts surveys on Maui several times a year, and on Molokai and Lanai annually. Her efforts have been focused on farms, nurseries and residences, and to date, have come up empty handed.
She’s looking for blotchy mottling on the leaves in an asymmetric pattern, “It’s the classic symptom.” according to Tauyan. When she finds this, or other indicators – such as yellowing leaves or misshapen, bitter fruit that don’t ripen – she collects samples and sends them to the University of Hawaii for testing. “We’ve been doing surveys since 2009. So far, we’ve had no positives.”
If citrus greening makes it to Hawaii, Tauyan thinks it will likely arrive in the form of an infected psyllid. Psyllids carry the disease for life. A miniscule psyllid slipping undetected into Hawaii could spell big trouble for our citrus trees, and inspectors with the Hawaii Department of Agriculture are on the lookout.
You can help. First, don’t bring citrus plant material into Hawaii from the Mainland or other parts of the world without first checking with the Hawaii Department of Agriculture. Secondly, regularly check your citrus. If the leaves are blotchy and mottled unevenly, or the fruit is misshapen and not ripening correctly your citrus could be infected. Confirming the diagnosis requires lab work, as there are also mineral deficiencies that resemble a greening infection. Contact Tauyan at (808) 973-9528 if you are concerned about your citrus plants or collect a sample yourself and submit it to the local extension office of the College of Tropical Agriculture and Human Resources in Kahului or Hoolehua on Molokai. Submission guidelines are online at www.ctahr.hawaii.edu/dnn/yellowdragon/SampleSubmission.aspx. Learn more about the disease and find an app for reporting possible cases of citrus greening at www.saveourcitrus.org.
* Lissa Fox Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Ki’ai Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.