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New insect, disease threaten Louisiana citrus

A new insect has joined the population of pests in Louisiana that can potentially destroy an agricultural crop. It’s the Asian citrus psyllid and its target is any kind of citrus tree.

Smaller than the capital A on this page and mottled brown, the psyllid sucks the sap out of leaves, resulting in curling. Sooty mold will develop on the leaves from the honeydew produced by the psyllid.

“The psyllid itself is not that much of a concern,” said Don Ferrin, LSU AgCenter plant pathologist. “The major threat is the bacterial disease it can spread — citrus greening disease.”

So far, one instance of citrus greening disease, which has no cure and slowly kills citrus trees, has been confirmed in Louisiana. And it’s on a backyard lime tree in Orleans Parish.

The diseased tree was brought to the attention of LSU AgCenter entomologist Natalie Hummel in late May. She then made the discovery of the Asian citrus psyllid’s presence in Louisiana.

“Now that the disease has been found, we need to take action to control the Asian citrus psyllid in nursery production, commercial groves and backyard plantings. The only way to manage the disease is to remove the psyllid and diseased trees,” Hummel said. “We have no idea how the psyllid got here, and we may never know.”

Only one other state, Florida, has citrus greening disease. Texas also has discovered the Asian citrus psyllid among its citrus trees, but so far there is no sign of the greening disease there, said Alan Vaughn, LSU AgCenter county agent in Plaquemines Parish, the hub of the $6 million dollar citrus industry in Louisiana.

The LSU AgCenter has joined forces with the Louisiana Department of Agriculture and Forestry (LDAF) and the U.S. Department of Agriculture’s Animal, Plant and Health Inspection Service (APHIS) to develop a plan to manage the psyllid and control its spread.

APHIS and LDAF officials are in the process of scouting Louisiana where citrus is grown for signs of the psyllid and the disease. So far, they have found the psyllid but not the disease in four parishes — Jefferson, LaFourche, St. Charles and Plaquemines.

“All citrus trees for retail sale are grown in Plaquemines Parish,” Vaughn said. “We are working very closely with the growers to prevent the disease from entering this parish. The nurseries are as big an industry as commercial fruit production.”

The Asian citrus psyllid can be managed by controlling movement of trees and through pest management practices. Pesticides are not currently available for backyard plantings of citrus trees.

“We are in the process of trying to get some additional pesticides approved for use by homeowners,” Hummel said.

Hummel is encouraging anyone who grows citrus trees to watch for signs of the psyllid or greening disease. If they suspect problems, they are advised to contact their local LSU AgCenter parish Extension office.

Another plant that serves as a host for the psyllid and the greening disease is the orange jasmine, also known as the Lakeview jasmine or the orange jessamine, said Dan Gill, LSU AgCenter horticulturist.

“Its official name is Murraya paniculata,” Gill said. “This ornamental with clusters of fragrant white flowers is also a primary host for the psyllid and greening disease. It’s a relative of citrus.”

Gill is not sure of the extent of this plant in southern Louisiana. Supplies from Florida were halted when the greening disease was discovered there in the late 1990s.

“If people have these plants in their landscapes, they need to keep an eye on them for the psyllid,” Gill said.

“We are in the process of training our parish agents on how to detect for the disease and the psyllid,” Hummel said. “The best way to get control of this situation is to assess how far the psyllid has spread.”

Symptoms of the greening disease include yellowing of the leaf midrib and veins and mottled appearance of the leaf. Seeds are aborted in the small, misshapen fruit, and the fruit will have a bitter taste.

“Unfortunately, these symptoms are a lot like symptoms of other diseases and nutritional deficiency,” Ferrin said. “The leaves must be tested in a laboratory to accurately determine if citrus greening disease is present.”

“I’m advising people with citrus trees to just be on the lookout for the psyllid,” Vaughn said. “The symptoms of the disease are just too similar to many other diseases and nutritional deficiency. I don’t want people unnecessarily cutting down their trees.

“The damage by the psyllid is very similar to the damage of the citrus leaf miner.”

“Food safety is not affected by this disease,” Gill said. “There’s nothing about this disease that would cause anyone to get sick from eating the fruit from a diseased tree.”

Florida has been living with this pest since 1998, and its industry has survived. “But, of course, Florida’s industry is huge,” Vaughn said. “They have the means to institute changes in the way they do business that are quite costly.”

Louisiana citrus growers may also have to make some changes in the way they run their operations to prevent the spread of this disease. The LSU AgCenter experts are taking what they can learn from Florida to develop a Louisiana plan of action.

“We have a lot of factors to weigh here before we make specific recommendations,” Vaughn said. “There are many unknowns both about the extent of the establishment of the psyllid and the greening disease.”

Louisiana citrus is harvested in the late fall and sold mostly in state. Especially popular are the Louisiana navel orange and the satsuma.

“We have a fairly active market in southern Mississippi, too,” Vaughn said.

The Louisiana citrus industry involves about 250 growers in 15 parishes. Citrus is sold by direct sales at roadside stands and farmers’ markets and retail at grocery stores and fruit stands.

Plaquemines is the leading citrus-producing parish with 500 acres of citrus with a gross farm value of $4.1 million.

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