Citrus Greening - Huanglongbing (Yellow Dragon Disease): A New Threat to Florida
Citrus greening, a potentially devastating disease to the Florida citrus industry, was identified in Miami-Dade County in early September 2005. Since then, additional cases have been confirmed in Broward, Palm Beach, and St. Lucie counties. More serious than citrus canker, it can result in diseased trees that bear unusable fruit and can die within five to eight years. Here are some important facts to know:
- Citrus greening is caused by a bacterium (Liberibacter asiaticus) and attacks the vascular system of plants.
- Once a tree is infected, there is no known cure.
- There are three known strains of the disease: Asian, African, and Brazilian. The strain found in South Florida appears to be the Asian one.
Citrus greening is transmitted by an insect vector, the citrus psyllid (Diaphorina citri). It may also be transmitted by grafting and field dodder, a parasitic weed; unlike citrus canker, it does not seem to be transmitted through casual contamination such as personal tools, wind, or rain. Asian citrus psyllids were first found in South Florida in 1998 and have since become dispersed across the state. The insect feeds on a variety of plants, including some important ornamentals.
Control of citrus greening will be particularly challenging because:
- The insect vector, citrus psyllid, is widespread.
- The frequency with which people move infected host plant material encourages spreading.
- Diseased trees may not show symptoms for up to one to five years or more.
- All varieties of citrus are susceptible, and the psyllid vector feeds on a wide variety of host plants, including the common orange jasmine (Murraya paniculata).
Pictured at right: Asian citrus psyllid adult and
citrus psyllid nymph
For the citrus greening pest alert and information, visit the Division of Plant Industry.
Citrus Greening Website
Citrus Greening Hotline: 1-800-850-3781
Identification of Citrus Greening
Symptoms of citrus greening can be spotted by foliar and fruit symptoms, which are similar to those of plants with severe nutritional deficiencies, including:
- Yellow shoots, twig dieback, and tree decline
- Older leaves developing a characteristic mottling or patchy discoloration
- Veins that are often prominent and yellow
- Fruit from infected plants with poor color and bad flavor; reduced size
- Severe fruit drop
- Similarity to zinc deficiency on new leaves
- Mottled pattern on older leaves
- Notched leaf from Asian citrus psyllid feeding
Currently, due to the direct exposure of citrus greening disease in South Florida, all citrus and citrus psyllid host plant material, including orange jasmine (Murraya paniculata), in Miami-Dade, Broward, and Palm Beach counties, is under quarantine. Shipments to citrus-producing areas outside the State of Florida (e.g., Arizona, California, Louisiana, Texas, Puerto Rico, etc.) is prohibited. Shipping within the state of Florida is permissible only through a signed compliance agreement with the Florida Department of Agriculture and Consumer Services, Division of Plant Industry. Terms of the compliance agreement must be followed explicitly and require all host plant material to be treated with an EPA-approved insecticide labeled for use in commercial ornamental nurseries. You must use a drench 10 days prior to shipment and a foliar spray two days prior to shipment. Approved products include Drench Foliar Spray Marathon Tame, Marathon II Dursban, and Chlorpyrifos Pro 4. (These products are restricted-use pesticides and subject to the requirements in FSS Chapter 487 and Rule 5E-9.)
Follow all applicable directions, restrictions, and precautions. Remember, the label is the law. For more information about the citrus greening compliance agreement, visit the Florida Department of Agriculture & Consumer Services Website at http://doacs.state.fl.us/pi/. Also provided is a list of plants known to carry citrus greening and a list of plants known to be hosts for the insect vector. In addition to the compliance agreement, each shipment of host plant material needs to be certified by an authorized representative of the Florida Department of Agriculture and Consumer Services, Division of Plant Industry. Once certified, a permit will be issued allowing shipment of the plant material. No shipments will be allowed to stock dealers such as Home Depot, Lowes', Target, etc.
Information provided in this article was obtained through the Florida Department of Agriculture, Division of Plant Industry, and the United States Department of Agriculture Animal and Plant Inspection Service.
Prepared by Michelle Leonard, Program Assistant, and Michael Orfanedes, Ph.D., Commercial Horticulture Agent
Photography credits: Jeffrey Lotz, Dr. Susan Halbert, and Dr. Xiaoan Sun, Division of Plant Industry