Plant City growers Richard and Martha Sue Skinner were proud of their citrus grove that had been in the family for four generations. But, more than 100 years of growth and tradition was wiped out in several years because of citrus greening.
The U.S. Agriculture Secretary Tom Vilsack hopes to prevent citrus greening from destroying more groves. He announced last week more than $1.5 million in funding to expand bio-control efforts to fight citrus greening, also known as Huanglongbing. This action is the first designation of funds by the Huanglongbing Multi-agency Coordination Group since it was established by Vilsack in December.
“Citrus greening poses a significant threat to the citrus industry and the thousands of jobs that depend on it,” Vilsack said. “It could also further drive up fruit and juice prices, if we don’t act.”
The funds have enabled USDA to sign cooperative agreements with the Florida Department of Agriculture and Consumers Services, the Texas Citrus Pest and Disease Management Corporation and the California’s Citrus Research Board and California Department of Food and Agriculture to coordinate the fight against citrus greening.
Previous USDA research funding to fight HLB includes commitments of about $1.5 million in each of the past three fiscal years by ARS in addition to NIFA steadily awarding increased grants from $878,000 in 2009 up to $10.4 million in 2012. Since 2006, the USDA has cumulatively invested more than $300 million on research efforts and actions associated with citrus health and combating citrus greening.
Skinner had to take out 900 of his trees when the disease first hit his grove. But, when the rest of his 2,500 trees started to show the same symptoms, he knew it was citrus greening.
Some of his trees were more than 100 years old. In 2011, the Skinners even got a visit from Florida Commissioner of Agriculture Adam Putnam, who presented them with the Century Pioneer Family Farm award for having such a long tradition of agriculture.
“I couldn’t wrap my arms around some,” Skinner said. “It’s sad when a tree goes from producing a box to nothing at all.”
A box is 90 pounds of fruit.
Skinner has watched as his neighbors on County Road 39 in Plant City fell to the same thing. Many have leased their land out to strawberry farmers. After citrus greening gripped his 50-acre grove, Skinner was able to secure aid from the Florida Department of Agriculture and Consumer Services Citrus Health Response Program. Through the program, he is able to recapture some of the costs it took when the trees were removed. He’s in his last year with the program and is deciding what to do with his land once his two years in the program are up.
CITRUS GREENING IN THE U.S.
According to the University of Florida’s IFAS: “HLB has seriously affected citrus production in a number of countries in Asia, Africa, the Indian subcontinent and the Arabian Peninsula, and was discovered in July 2004, in Brazil. Wherever the disease has appeared, citrus production has been compromised with the loss of millions of trees.”
The psyllid was first found in 1998, in Palm Beach County, on back yard plantings of orange jessamine, the University of California Agriculture & Natural Resources reported. In August 2005, citrus greening was found in the South Florida region of Homestead and Florida City. Since that time, citrus greening has been found in commercial and residential sites in all counties with commercial citrus.
Richard Skinner first noticed his grove ailing about five years ago.
“The first signs are not quite as obvious to what it is,” Skinner said. “It could be that the tree isn’t getting enough nutrition, other diseases.”
HOW IT SPREADS
Citrus greening is thought to be caused by the bacterium, Candidatus Liberibacter asiaticus. It is spread by the Asian citrus psyllid, a tiny non-native pest. The psyllid takes the bacteria into its body when it feeds on bacteria-infected plants. The disease spreads when a bacteria-carrying psyllid flies to a healthy plant and injects bacteria into it as it feeds.
THE SIGNS
An initial sign of citrus greening is vein yellowing and an asymmetrical chlorosis referred to as “blotchy mottle.”
“Leaves may be small and upright with a variety of chlorotic patterns that often resemble mineral deficiencies such as those of zinc, iron, and manganese. Some leaves may be totally devoid of green or with only green islands,” according to the University of Florida.
Growers also can mistake the symptom for Phytophthora root rot, water logging, citrus blight or leafminer tunnels.
GROVES VS. RESIDENTIAL
Although citrus greening doesn’t discriminate between trees, Skinner believes homeowners shouldn’t panic about theirs.
There’s a domino effect in the groves, because the trees are so close together. The infected Asian citrus psyllid has easier accessibility to spread the disease. But, as a nursery owner, he sees most of his clients only have a maximum of four citrus trees. Skinner advises spraying the trees with a fruit tree oil to deter the Asian citrus psyllid from landing on the trees.
ASIAN CITRUS PSYLLID
“The Asian citrus psyllid, Diaphorina citri Kuwayama, has become the most important insect pest of Florida citrus due to the presence of citrus greening
disease also known as huanglongbing, which is spread by the psyllid,” according to the University of Florida.
The tiny brown insect feeds on all varieties of citrus. It originated in Asia or India and then spread to other areas of the world where citrus is grown.
It was found in 1998, in Florida and spread through the state, primarily due to the movement of infested nursery plants.
THE BIGGER BUG
Part of the funds will increase significantly the production of the parasitic wasp known to control populations of Asian citrus psyllid.
“They are piggybacking off something that happened 20 years ago,” Richard Skinner said.
Skinner is talking about citrus leafminers and their parasitic nemeses, Ageniaspis citricola. Leafminers are tiny moths that hide within the plant canopy during the day and lay eggs on young leaf flushes at night. The larva emerges directly into the leaf tissue, mining along the midvein and making its way to the leaf margin. The mining makes the leaves susceptible to canker infections by creating wounds in leaf tissue.
Shortly after leafminers were discovered in 1993, in Florida, the parasistoid Ageniaspis citricola was released for biological control of them statewide. It would lay its own eggs in the larvae of the leafminers. The parasitoid established itself throughout the citrus growing regions of the state and joined a number of native parasitic wasps in attacking the pest.
The wasp that will take on the Asian citrus psyllid is called the Tamarixia radiata. It is a small, brown insect that doesn’t sting or bite humans or animals. It was first imported to Florida from Taiwan and south Vietnam, and between 1999 and 2001, about 37,000 adults of a mixed colony from the two origins were released in Florida citrus. It is originally identified from northwestern India, now part of Pakistan.
“They probably hope the wasps will have the same effect,” Skinner said. “They’re not going to eradicate it. The jury’s out on that one, but it’s not in the cards. It might keep (the Asian citrus psyllids) in check, but it won’t completely eradicate them.”
Funding also will go to other biocontrol methods such as thermal therapy or ways to enrich the soil to make them less susceptible to disease.