Citrus Greening

Citrus greening on leaf and on fruit

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

What is Citrus greening?
Citrus greening is a bacterial disease (Candidatus Liberibacter asiaticus) that lives in the vascular tissue of the plant. It accumulates and blocks the vessels of the plant. The disease can be difficult to identify at first glance and appear similar to a nutritional deficiency. Symptoms are expressed as yellow leaves with a blotchy, irregular coloring. 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 citrus can be infected and how?

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

Citrus Psyllid

All species in the citrus genera can be infected with Citrus greening. This includes, but is not limited to oranges, grapefruit, lime, lemons and satsumas. Additionally susceptible are kumquats, trifoliate orange (used for rootstock), calamondin and others. Citrus greening does not infect humans or pets.

The disease is transferred by the Asian Citrus Psyllid (Diaphorina citri). 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 a 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 cure an infected tree?
There is no treatment for a tree infected with Citrus greening. It is always best to contact your local county agent for further research and potential action to have your tree tested. 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 by controlling the psyllid.

How do I prevent it?

Picture of parastic wasp, Tamarixia

Picture courtesy of Mike Lewis.

Beneficial insects can reduce the amount of psyllid nymphs on your tree. These include parasitic wasps and various predators, including lady beetle, syrphid fly, and lacewing larvae. Some spiders, birds, and other general predators feed on adult psyllids.

Chemical options include broad spectrum foliar pesticide sprays containing active ingredient carbaryl or malathion. With foliar application, spray on the underside of the leaves in order to direct the product to the insects. Pesticides containing active ingredient imidacloprid are available as a spray or as a soil drench. Careful consideration should be made regarding use of systemic pesticides as they should be applied when the tree is not in bloom to reduce instance affecting insect pollinators. Only use pesticides that are labeled for citrus trees when spraying your trees. Read pesticide product labels carefully and explicitly follow instructions for application rates and scheduling, protective equipment as applicable as well as warning indicators for your and environmental health.

Organic chemical pesticides such as horticultural oils and soaps can also be used, but these will need to be sprayed every 7 -10 days to be effective.  For other options, including organic options, see the Texas Department of Agriculture Texas Citrus Greening website. IMPORTANT: Transportation of citrus plants out of the quarantined areas is strictly prohibited.

Is Brazoria County in quarantine for Citrus Greening?
Gulf Coast Quarantined Area. As of October 7, 2019, TDA has expanded  previously quarantined area to include all of Brazoria, Fort Bend, Galveston, Harris and Montgomery counties in the State of Texas.

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. There are additional counties quarantined in South Texas. 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 Brueggerhoff to schedule a tree inspection. The agent will recommend the tree to be tested if it looks infected. While there is not a fee for the site visit, there are associated fees involved with the testing. You can also send a vegetative sample to the Texas A&M AgriLife Plant Disease Diagnostic Laboratory; click here to discover how to send in samples.

For More Information About Citrus Greening

Gulf Coast Citrus Greening Quarantine Fact Sheet

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 Elizabeth McMahon, CEA- Horticulture

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