Citrus greening
A serious bacterial disease of citrus spread by the Asian citrus psyllid that causes blotchy yellow leaves and small, bitter, misshapen fruit.
Also known as: Huanglongbing, HLB, Yellow shoot disease
Symptoms and identification
Leaves show an irregular, blotchy yellow mottle that does not match the pattern of nutrient deficiency, which is usually symmetrical along the leaf veins. Fruit stay small, lopsided and partly green, taste bitter and have aborted seeds. Branches die back and the tree declines over a few years.
Causes
The bacterium Candidatus Liberibacter is spread by the Asian citrus psyllid and by grafting infected plant material. The psyllid feeds on new growth, and curry leaf and orange jasmine can also host it.
Organic treatment
There is no cure. Report suspected trees to the local agricultural authority and remove infected trees as advised. Control psyllids with neem or insecticidal soap on new growth.
Prevention
Buy only certified disease-free trees, do not move citrus or curry leaf cuttings between regions, and control psyllids on new flushes. Follow local quarantine rules.
Chemical treatment (use with care)
Systemic insecticides labelled for Asian citrus psyllid reduce spread but do not cure infected trees. Follow the label and local advice.