Citrus canker, a serious bacterial disease, has spread to local fruit trees

July 30, 2013
When I started my horticultural career in New Orleans back in 1980, my memory of growing citrus seems so easy. White flies and other sucking insects and the sooty mold they caused were the only major problems.

A few applications of oil sprays were all that was needed, perhaps with some Malathion added. Diseases were hardly ever an issue. Freezing temperatures were the major problem in the ’80s.

My, how times have changed. Many new insects and diseases have shown up in our area since then.

Citrus trees are the most popular fruit trees grown in the home landscape, and are commonly found in yards from Bogalusa to Baton Rouge, Lake Charles to Lafayette and New Orleans. Commercial citrus production takes place primarily in Plaquemines, St. Bernard, Lafourche and Terrebonne parishes.

Citrus leaf miners were first found in Plaquemines Parish in May of 1994. Can you imagine a time when the new growth on our citrus trees in late summer was not twisted and mangled by citrus leaf miner larvae tunneling inside? Spinosad (various brands) can be sprayed as the new growth appears to help reduce the damage.

In the summer of 2008, the Asian citrus psyllid was found along with the citrus greening disease it transmits from tree to tree. Citrus greening disease, which has only been found in Orleans and Washington parishes, is caused by a bacterium. It leads to the gradual decline and death of an infected tree. There is no cure.

A fungal disease called sweet orange scab was found in Louisiana and Texas in the summer of 2010. Copper fungicide sprays in spring are helpful in controlling this disease.
If you see symptoms that match those of citrus canker, do not remove or destroy the tree yourself.

In just the past few years, the wooly white fly and black fly have shown up here. They are sucking insects that cause heavy amounts of black sooty mold to occur, and the black fly is more difficult to control than the white fly.

I’m probably missing some, but the real reason for this column is a serious bacterial disease that was discovered here just last month – citrus canker.

Citrus Canker

Florida was the first state where citrus canker was discovered, and that was back in 1910. By 1914, it had spread to a number of southeastern states, including Louisiana.

It was declared eradicated in Florida in 1933 and in Louisiana in 1940. It was detected in Florida again in 1986 and declared eradicated in 1994.

Unfortunately, it was detected for a third time in 1995, and eradication efforts began again. In 2006 the eradication program was ended, without achieving eradication. So you see what we are up against.

Citrus canker originated in Southeast Asia and has spread to citrus growing areas in several countries. It can affect every type of citrus we grow. It was found in Louisiana on June 21 by a USDA employee familiar with this disease jogging in City Park.

At this time, six sites have been officially confirmed positive, five in the area of New Orleans City Park and one at Lakefront Airport. Four of these trees have been voluntarily removed. There are two more residential sites, one in New Orleans East and one in Kenner, and initial lab tests indicate these are citrus canker positive.

Citrus canker symptoms include brown spots on leaves, often with an oily or water-soaked appearance. The spots (technically called lesions) are usually surrounded by a yellow halo, and they can be seen on both the upper and lower sides of the leaf. Similar symptoms can appear on fruit. Even stems can have symptoms with brown bumps or lesions.

As the leaf spots age, they become crusted and tan surrounded by a yellow ring. Eventually, the tan tissue can fall out creating a hole through the leaf. Leaf spots have been described as looking like a cigarette burn surrounded by a yellow circle.

The disease causes citrus trees to prematurely drop leaves and fruit, and it can cause dieback of twigs and branches. With time, trees quit producing fruit and decline in health. (These symptoms can also be caused by Phytophthora root rot, but the leaves do not have spots when the problem is root rot.)

The bacterium responsible for the disease is spread from infected trees to healthy trees by wind-driven rain or on contaminated tools, clothing and equipment. It can move long distances on equipment, in large storms such as hurricanes and by the movement of infected citrus materials. It is not transmitted by insects.

There is no effective treatment for infected trees. They must be removed.

Do your part

It is very important that home gardeners check their citrus trees for citrus canker symptoms. This includes all citrus — satsuma, kumquat, orange, sour orange, grapefruit, lemon, lime, calamondin, tangerine and trifoliata orange.

If you see symptoms that match those of citrus canker, do not remove or destroy the tree yourself. Do not take samples to area nurseries or LSU AgCenter Extension offices for diagnosis.

Report suspected citrus canker infected trees to the Louisiana Department of Agriculture at 225.952.8100 or the U.S. Department of Agriculture state plant health director Bill Spitzer at 225.298.5410 (or email and follow the directions you are given.

Surveys for citrus canker by agents with the USDA Animal and Plant Health Inspection Service and Plant Protection and Quarantine are ongoing around the area, and you may see survey teams collecting citrus tree samples in your area or neighborhood.

At this time, everyone should avoid moving around citrus materials, such as trees, fruit or trimmings, as much as possible.

The Louisiana Department of Agriculture and Forestry maintains a state quarantine that prohibits the movement of citrus plants grown in others states from entering Louisiana (although, unfortunately, people routinely order citrus trees from mail order nurseries, and I imagine even bring back citrus trees from other states).

This restriction is in place to help protect against the introduction of insect pests and diseases, such as citrus canker, and this is why it is so important that home gardeners not bring in citrus trees from other states or move citrus trees around. Also, citrus trees cannot be moved out of Orleans or Washington parishes due to federal and state citrus greening quarantines already in place.

Citrus canker
Citrus canker

There is no reason to believe that our Louisiana citrus industry is infected by citrus canker. Louisiana’s citrus industry receives routine inspections from USDA and LDAF personnel, and to date, no citrus canker has been found associated with our citrus fruit orchards or citrus nursery plant production.

It is important that anyone purchasing a citrus tree buy only Louisiana-grown plants and purchase only from growers or dealers who are operating under a permit with the LDAF.

I recommend you visit a new USDA website called Save Our Citrus.You can also view the LSU AgCenter fact sheet on citrus canker.

Don’t panic and don’t worry that this is the end of citrus in Louisiana. Remember, Florida has been dealing with this disease for decades, and it’s still a major citrus producer.

But, let’s be especially vigilant and pay attention to information coming out on this potentially devastating disease. That way, we can all do our part to minimize the impact of citrus canker as much as possible. Courtesy nolamedia

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