Kaffir lime (Citrus hystrix) is a slow growing tree native to Southeast Asia. Its leaves are popular in Thai cooking. In the United States, kaffir lime trees are often quarantined and trade is restricted.
The leaves of kaffir lime can be infected with citrus greening disease, also known as huanglongbing (HLB) or yellow dragon disease. The disease is caused by bacteria and spread by insects. It affects the plant's vascular system and kills all infected plants.
Yellow shoots appear on the tree and twigs begin to die. Mottled patches appear on older leaves and veins may turn yellow. Leaves will also begin to drop off. Fruit doesn't develop properly, tastes badly and drops from the tree earlier than it should. The tree will decline and eventually die.
To help limit the spread of citrus greening disease, all or part of the states of Florida, California, Arizona, Georgia, Louisiana, South Carolina, Hawaii, Mississippi, Alabama and Texas have quarantines on citrus trees, including kaffir lime, or quarantines on the insects responsible for spreading the disease. Trade in plant material may be restricted in these areas.