Citrus Greening (Huanglongbing)
Candidatus Liberibacter asiaticus
Overview
Citrus greening, also called huanglongbing (HLB), is associated with Candidatus Liberibacter bacteria spread by the Asian citrus psyllid and related vectors. It is one of the most serious citrus diseases worldwide. The pathogen disrupts phloem function, causing chronic decline. There is no widely available cure for backyard or commercial trees once infected. Management focuses on vector control, removing infected trees where required, and supporting tree health while researchers and breeders develop more tolerant citrus.
Symptoms
Leaves show blotchy yellow mottling that is not confined to veins the way nutrient deficiencies often are. Shoots may be stunted with upright, sparse growth. Fruit can be small, lopsided, bitter, and poorly colored, sometimes remaining green at the stylar end. Root systems decline as the disease advances. Trees gradually lose canopy and productivity over months to years. Psyllid nymphs and adults may be found on new flush during inspections.
Environmental Conditions
Hot
Prevention
Plant only certified disease-free citrus from reputable nurseries. Inspect new flush regularly for psyllids and remove heavily infested flush on small trees when practical. Avoid moving citrus plants, budwood, or cuttings from infected areas. Encourage beneficial insects that prey on psyllids by limiting broad-spectrum sprays. In regions where greening is established, prioritize tolerant rootstocks and cultivars as they become available, and maintain tree vigor so decline is slower.
Management
Confirm diagnosis with extension or laboratory testing when possible, because nutrient issues can mimic blotchy yellowing. Follow regional guidelines for removing infected trees to protect neighboring citrus. Manage psyllids with reflective mulches, careful monitoring of flush, and least-toxic options that spare beneficials when practical. Keep trees watered and mulched to reduce additional stress. Nutritional programs that support canopy health may temporarily improve appearance but do not eliminate the pathogen.