Citrus greening (HLB)
Blotchy asymmetric leaf mottle, yellow shoots and small, lopsided, bitter, green-ended fruit — a psylla-spread bacterium that kills the orchard slowly.
- Pathogen
- Bacterium (Ca. Liberibacter asiaticus)
- Spreads by
- Citrus psylla; infected budwood
- Favoured by
- Psylla activity; infected planting material
- Main risk
- Tree decline; small bitter unsaleable fruit
Overview
Citrus greening, or Huanglongbing (HLB), is the most destructive disease of citrus in the world. It is caused by a phloem-limited bacterium (Candidatus Liberibacter asiaticus in India) spread by the citrus psylla (Diaphorina citri) and through infected budwood/planting material. The classic leaf symptom is a blotchy, asymmetric yellow mottle that does not match on the two halves of the leaf (unlike a nutrient deficiency, which is usually symmetric), often with leaves that are small, upright, thickened and leathery, and shoots that turn yellow.
On fruit it causes small, lopsided (asymmetric) fruit that colour poorly and stay green at the bottom end (hence "greening"), with aborted, dark seeds and a bitter, off taste. Affected trees decline over years — twig dieback, sparse foliage, heavy fruit drop — and become unproductive. There is no cure. Management is area-wide and preventive: plant only certified disease-free budded plants, control the citrus psylla vigorously, and rogue out and destroy infected trees so they cannot serve as a source.
How to identify it
- A blotchy, asymmetric yellow mottle on leaves that does NOT match on the two halves — the key clue that separates it from a (symmetric) nutrient deficiency.
- Small, upright, thickened, leathery leaves and yellowing (often one-branch-at-a-time) shoots.
- Small, lopsided fruit that colour poorly and stay green at the bottom end, with dark aborted seeds and a bitter taste.
- Slow tree decline — twig dieback, sparse canopy, heavy fruit drop, falling yield over years.
What causes it and when
- A phloem-limited bacterium (Candidatus Liberibacter asiaticus) spread by the citrus psylla (Diaphorina citri) and through infected budwood/planting material.
- Psyllas feeding on tender new flush pick up and transmit the bacterium, so spread tracks psylla activity and flushing.
- Planting infected budded plants introduces the disease directly into a new orchard.
- Once infected there is no recovery — the tree declines and stays a source of infection.
Cultural & organic control
- Plant only certified, disease-free budded plants raised from clean budwood — the foundation of control.
- Inspect regularly and rogue out and destroy infected trees promptly so they stop serving as a source (after dealing with the psylla).
- Manage the citrus psylla, especially on the tender new flush, and control ants that protect it.
- Keep trees healthy with balanced nutrition and remove nearby neglected/infected citrus and alternate hosts.
Chemical (vector) control
- The bacterium cannot be sprayed — control the citrus psylla to slow spread, timing sprays to the new flush when psylla and transmission peak.
- Use CIB&RC-registered insecticides for the psylla judiciously (rotating groups) as part of area-wide management.
- Before roguing an infected tree, control its psylla so they do not migrate to healthy trees, where recommended.
- Confirm the current psylla-management and roguing protocol for your area with your local KVK.
Prevent it coming back
- Establish and replant only with certified disease-free plants from clean budwood.
- Keep controlling the citrus psylla on every flush and rogue infected trees as soon as confirmed.
- Work area-wide with neighbours — greening is not controlled in one orchard alone — and remove neglected/infected citrus.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My citrus leaves have a blotchy yellow mottle and the fruit are small and lopsided. Is this a deficiency?
Possibly not — a blotchy yellow mottle that is asymmetric (does not match on the two halves of the leaf), with small upright leathery leaves, yellow shoots and small, lopsided, poorly-coloured, bitter fruit that stay green at the bottom, points to citrus greening (HLB), not a nutrient deficiency (which is usually symmetric and improves with the nutrient). Greening has no cure; control the citrus psylla, rogue infected trees, and replant only certified disease-free plants.
How do I tell citrus greening from a zinc or iron deficiency?
The most useful clue is symmetry. Zinc and iron deficiencies usually give a fairly symmetric interveinal yellowing that matches on both halves of the leaf and improves when you correct the nutrient. Citrus greening gives a blotchy, asymmetric mottle that does not match across the midrib, together with small lopsided bitter fruit, one-branch-at-a-time yellowing and slow tree decline, and it does not respond to feeding. When in doubt, get it tested before deciding.
Why is citrus greening so hard to control?
Because there is no cure once a tree is infected, it spreads readily through both the citrus psylla and infected planting material, and an infected tree keeps declining while acting as a source for the psylla to spread to healthy trees. It is only held back by area-wide, preventive effort: certified disease-free plants, vigorous psylla control on every flush, and prompt roguing of infected trees — and it cannot be managed in one orchard while neighbours ignore it.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.