Citrus Greening

Citrus greening on leaf and on fruit

Picture courtesy of Dr. Susan Halbert and Dr. Timothy S. Schubert

What is it?
Citrus greening is a bacterial disease. The Candidatus bacterium lives in the vascular phloem tissue of the plant. It accumulates and blocks the vessels of the plant, causing death. In human terms, the plant basically dies of a stroke (but it isn’t as quick as a stroke). The disease can be tricky to identify. Symptoms are yellow leaves with a blotchy, irregular coloring. The symptoms will be similar to a nutritional deficiency, except that the coloring will be irregular. Fruit set is low and the fruit that is present will be oddly colored and distorted. Trees infected with the disease die slowly, usually lasting about 3-10 years. The disease has been found in Florida, Louisiana, South Carolina and Georgia, in addition to Cuba, Brazil and Mexico. It is also known as Huanglongbing or Yellow Dragon disease.

What gets it and how?

A picture of the citrus psyllids on the underside of a citrus leaf

Citrus Psyllid

All species in the citrus genera can get Citrus greening. This includes, but is not limited to, oranges, grapefruit, lime, lemons and satsumas. Additionally susceptible are kumquats, trifoliate orange (used for rootstock), calamodin, box orange, curry leaf, orange jasmine, limeberry and others. Citrus greening does not infect humans or pets.

The disease is transferred by the Asian Citrus Psyllid. The psyllid feeds at a peculiar 45 degree angle on the underside of mature leaves and new growth. They feed by sucking sap out of the plant. Eggs are a bright yellowish orange to pure orange. The eggs hatch into the child or nymph stage. They nymphs are yellowish orange in color and have two red eye spots. The psyllid is currently found in Brazoria County.

 

How do I treat it?
There is no treatment for Citrus greening. As of now, it is best to immediately remove the tree if it tests positive for citrus greening. Since Brazoria County is not in quarantine, it is best to have your trees tested before getting them removed.
Current research is looking into building genetic resistance into citrus trees, including using spinach DNA. The best method for you is to prevent the disease from infecting your tree.

How do I prevent it?

Picture of parastic wasp, Tamarixia

Picture courtesy of Mike Lewis.

Beneficial insects can be used to reduce the amount of psyllids on your tree. These include parasitoids like Tamarixia and predatory lady bugs. Chemical options include broad spectrum foliar pesticide sprays such as carbaryl or malathion. These chemicals are also harmful to beneficial insects such as bees. Applications of carbaryl or malathion may increase population of pest insects such as aphids on your plant. When applying, spray on the underside of the leaves in order to kill all the insects. Only use pesticides that are labeled for citrus trees when spraying your trees. Imidacloprid is a pesticide that is available as a spray or as a soil drench. The tree sucks up the insecticide, and the insect dies when it bites the plant. Control is more long term that a foliar spray.

The soil drench should be applied in the summer or fall, WHEN THE PLANT IS NOT BLOOMING or ABOUT TO BLOOM. Citrus trees can be bee pollinated, and it will be toxic to the bees if you apply at this time. Read the pesticide instructions for how much to apply and for further information. ALWAYS FOLLOW THE PESTICIDE LABEL AND IF THE PESTICIDE IS NOT LABELED FOR THE PLANT, DO NOT USE IT FOR THE PLANT. Horticultural oils and soaps can also be used, but these will need to be sprayed every 7-10 days.  For other options, including organic options, see the Texas Citrus Greening website. Be very careful when buying citrus trees on the internet. Do not buy citrus trees from a quarantined area, or bring citrus trees in from a quarantined area

What do you mean by quarantine? Is Brazoria County in quarantine for Citrus Greening?
The citrus greening quarantine prohibits any citrus plants, fruit, equipment or items made with citrus (floral arrangements, wreaths, potpourri or seasonings like kaffir lime leaves) being moved from quarantined areas. It is illegal to move citrus trees or materials from quarantined areas, and you could be subject to a fines ranging from $1,000 to $60,000. Currently in our area Fort Bend, Harris and Montgomery County are quarantined (last updated 7/21/2015). There are additional counties quarantined in South Texas. Brazoria County is not quarantined as of this time (last updated 7/21/2015). You are welcome to call your local county extension office for up to date information.

What do I do if I suspect my tree has Citrus greening?
Email
or call Brazoria County Horticulture Extension Agent Stephen Brueggehroff to come and inspect the tree. Mr. Brueggerhoff will recommend the tree to be tested if it looks infected. There is no charge for the site visit, but there is a charge involved with the testing. You can also send a vegetative sample to the Texas A&M AgriLife Plant Disease Diagnostic Laboratory, and there will be a fee associated for this service; click here to discover how to send in samples.

I would like more information about citrus diseases

Citrus Greening Links

Aggie Horticulture Citrus Greening Page

South Texas Citrus Alert

Texas Department of Agriculture

University of California’s Interactive Citrus Greening webpage

The Short List of Citrus Information; created by Brazoria County AgriLife Extension Horticulture

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