Download Look out for Citrus Greening (Huanglongbing)

Plant Pest Threat - Citrus greening
Look out for Citrus Greening (Huanglongbing)
In leaves, a pale yellow colouring with green, irregular areas
(mottling) can be observed
Source: National Pest Surveillance & Monitoring Systems - SENASA
(Health & Quality Agrifood National Service).
General information
One of the worst problems in citrus trees is Citrus greening also known as Huanglongbing (HLB) - a bacterial
disease that has no known cure. It grows in the tissue of citrus plants and eventually causes the tree to die.
Citrus greening invades the plants nutrient conducting tissues, causing a decline of citrus trees and rendering
them unproductive.
Citrus greening probably originated in Africa. It seriously affects production in parts of North America, South
America, Africa, Asia and the Middle East.
It is transmitted by psyllids that are not present in Australia but it can also be spread in infected grafting
material.
Early detection of this disease and the psyllid insects that spread it, should any arrive in Australia, is vital to
ensure the best chance of eradication. Preventing entry of this disease and its vector is the most effective
method of protecting our valuable citrus industry.
What do I look for?
Symptoms of Citrus greening tend to closely resemble those of nutrient deficiency, making it difficult to
diagnose early in an outbreak, especially in unthrifty or nutrient-deficient trees.
Citrus greening infection often starts with production of a singly chlorotic (yellow) shoot that contrasts against
an otherwise green canopy. Leaves can show chlorotic blotchiness or mottling. A key differentiator between
Citrus greening infection and nutrient deficiency is that Citrus greening symptoms tend to be asymmetric,
while nutrient deficiency is the same on both sides of the leaves mid-vein. Similarly affected fruit are often lopsided. Veins can become yellow, swollen and/or corky.
Advanced or chronically infected trees show yellowing of the entire canopy with sparse foliage and severe
twig dieback. Fruit are small, lopsided, tend to remain mostly green even when mature and are bitter.
Any suspicious symptoms of the disease will need to be confirmed by using one of several laboratory
detection methods.
Plant Pest Threat - Citrus greening
Hosts
The disease affects all citrus cultivars, species and hybrids. Sweet orange and mandarin are severely
affected; grapefruit, lemon and pomelo less so. Mexican lime and trifoliate orange are the least affected.
In fruits, there may be there may be deformities and asymmetry, Source: Nation al Pest
Surveillance & Monitoring Systems - SENASA (Health & Quality Agrifood National Service).
Spread of disease
The disease can be spread by grafting, but transmission rates can be variable due to the irregular distribution
of the bacterium in the tree. It is possible to propagate a disease-free plant from an infected one.
Two psyllid insects are important vectors (agents of spread) of the disease. Diaphorina citri is found in Asia
and Trioza erytreae is found in Africa.
D. citri, commonly called the Asian citrus psyllid, is the insect of most concern to Australia due to its proximity
and its tolerance of warm temperatures. Adult Asian citrus psyllids are small, up to 2.5 mm, resemble small
cicadas and prefer to feed on leaves and stems of citrus and closely related Rutaceae. They have mottled
brown wings, characteristically sit at an angle to the shoot or leaf on which they feed and will jump when
disturbed. Eggs are bright yellow and deposited on the underside of young leaves.
The Asian citrus psyllid is most likely to be found on new shoots, and the population increases during periods
of active plant growth.
Adult Asian Citrus Psyllid showing characteristic
feeding position. Source: David Hall, USDA
Agricultural Research Service.
If you see anything unusual, call the Exotic Plant Pest Hotline 1800 084 881
Plant Pest Threat - Citrus greening
Supported By
Queensland Government
Department of Agriculture, Fisheries and Forestry
New South Wales Government
Primary Industries Biosecurity
ACT Government
Territory and Municipal Services
Victorian Government
Department of Environment and Primary Industries
Tasmanian Government
Department of Primary Industries, Parks, Water and Environment
South Australian Government
Primary Industries and Regions
Western Australian Government
Department of Agriculture and Food
Northern Territory Government
Department of Primary Industry and Fisheries
Commonwealth Government
Department of Agriculture
Disclaimer
The material in this publication was prepared from the most up-to-date information available at the time of
publication. It is intended as a guide only and the publisher accepts no responsibility for errors.
Revised
November 2013