Huanglongbing (citrus greening) on orange — symptoms and treatment

Severity: high

What is Huanglongbing (citrus greening)

Huanglongbing (citrus greening) is caused by Candidatus Liberibacter bacteria, spread by psyllid insects, and it is the most devastating citrus disease worldwide. The bacteria live in the phloem — the tissue carrying sugars from the leaves to the rest of the tree — and clog it, so the tree starves in pieces. Severity is rated high, and that undersells it: there is no cure for infected trees. An infected orange tree declines and dies, and everything you do is about protecting the trees still clean.

Symptoms

The signature is asymmetric blotchy mottling of the leaves — irregular patches of yellow and green across the blade, and the asymmetry is the point: the pattern does not match across the midrib, so one side of the leaf differs from the other. That distinguishes it from nutrient deficiencies, which are symmetrical about the midrib. Alongside it you see yellow shoots, branches turning yellow while the rest of the tree still looks well. The fruit gives it away too: lopsided, bitter fruit that stays green, small and misshapen. Untreated, the outcome is tree decline.

Key signs:

• Early: asymmetric blotchy mottling — yellow and green patches that do not mirror across the midrib
• Early: yellow shoots on an otherwise healthy-looking tree
• Advanced: lopsided, bitter fruit that stays green
• Advanced: progressive tree decline

The asymmetry test is the one to remember: zinc deficiency and similar disorders yellow evenly on both sides of the midrib; greening does not.

Causes and conditions

The disease travels by insect. Psyllids feed on citrus, pick up the bacteria from an infected tree, and inject them into the next tree — one insect visit is enough. That single fact defines the management strategy: you cannot treat the bacteria in the tree, so you fight the vector and remove the sources. Psyllids breed on flushes of new growth, so a tree pushing tender shoots is where populations build. It also moves long distances in infected nursery stock and budwood, which is how it reaches regions no psyllid could have flown to. Infected trees stay infectious as long as they stand.

Treatment

There is no cure. Nothing here treats an infected tree — it protects the healthy ones.

Remove infected trees — cultural

Upon detection. Remove and destroy infected trees promptly to reduce inoculum source. Plant certified disease-free nursery stock. Promptly is the operative word: every day an infected tree stands, psyllids feed on it and carry the bacteria to your remaining trees. Removal is not giving up — the tree is already lost — it is protecting the rest. Certified stock keeps you from planting the disease yourself.

Imidacloprid (psyllid control) — chemical

Year-round vector control. Control Asian citrus psyllid vector with systemic insecticides. No cure for infected trees. Vector control is year-round because a single feeding psyllid transmits — a gap in coverage is an opening. It protects healthy trees but does nothing for one already carrying the bacteria. Pre-harvest interval: 60 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Plant only certified disease-free nursery stock — never unknown budwood or gift trees.
• Control the psyllid vector year-round rather than seasonally, and inspect new flushes where psyllids breed.
• Remove and destroy infected trees as soon as they are identified.
• Report suspected cases where reporting is required — this is a regulated disease in many countries.

Frequently asked questions

Can I save an infected tree? No. There is no cure for infected trees. Removing it promptly protects the trees around it, because as long as it stands psyllids carry the bacteria from it to your healthy trees.

Is it contagious to my other citrus? Yes, and to all citrus. Psyllids carry it tree to tree, and infected planting material much further. This is why vector control and removal are the whole strategy.

Can I eat fruit from an infected tree? The fruit is not harmful, but it is lopsided, stays green and tastes bitter — most people find it unpalatable. After Imidacloprid, respect the 60-day interval.