Citrus greening, also called Huanglongbing (HLB), shows up as an asymmetric yellow mottling on leaves, lopsided and partially green fruit, and a thinning canopy that worsens over time. The tricky part is that the disease does serious damage underground long before the tree looks obviously sick. By the time the canopy visibly declines, the tree has already lost more than 70% of its root system.
The Signature Leaf Pattern
The most recognizable sign of citrus greening is a blotchy, irregular yellowing on the leaves. Patches of light green or yellow appear against the normal dark green, and these patches are asymmetric, meaning the pattern on one side of the leaf’s central vein doesn’t mirror the other side. This is the single most important visual clue, because it separates HLB from nutrient deficiencies that can look superficially similar.
The yellowing happens because the bacteria block the leaf’s internal plumbing (the phloem), which traps starch inside the leaf tissue. That trapped starch crushes and destroys chloroplasts in an irregular pattern, creating the distinctive mottled look. The damage is random, so no two leaves look exactly the same. You might see a large yellow blotch on one half of a leaf and nearly normal green on the other.
A simple way to check: mentally draw two small circles on opposite sides of the midrib, directly across from each other. If the color and pattern inside both circles look like mirror images, you’re probably looking at a nutrient issue. If the two circles look noticeably different from each other, that asymmetry points toward citrus greening.
How It Differs From Nutrient Deficiencies
Zinc deficiency produces a yellow mottle between the veins that is symmetrical across the central vein. In severe cases the leaves become small, narrow, and pale, which can overlap with late-stage HLB symptoms. Manganese deficiency looks similar to zinc deficiency, with light green and dark green banding, but again the pattern is symmetrical and typically appears on younger leaves. Both deficiencies create an even, predictable pattern. HLB does not.
At later stages of citrus greening, the tree often develops genuine nutrient deficiencies on top of the disease, because damaged roots can no longer absorb minerals effectively. This makes identification harder over time. The key is catching the asymmetric mottle early, before secondary deficiency symptoms pile on and blur the picture.
What the Fruit Looks Like
Fruit from infected trees is one of the more dramatic visual signs. Oranges, grapefruits, and other citrus may ripen unevenly, staying partially green on one end while the rest of the fruit changes color. The shape is often lopsided or irregular rather than round. Seeds inside may be small, dark, or aborted. Over time, the tree produces fewer fruit overall, and the ones it does produce are noticeably smaller than healthy fruit from the same variety.
Cutting an infected fruit open reveals another clue: the juice inside tastes distinctly off. Researchers describe it as bitter, sour, salty, metallic, and musty, with very little of the sweetness or fruity flavor you’d expect. The bitterness comes from elevated levels of compounds called limonin and nomilin, which spike in symptomatic fruit. The juice also has higher acidity, lower sugar content, and a poor sugar-to-acid ratio. Even if the fruit looks only slightly abnormal on the outside, the flavor is often strikingly wrong.
Canopy and Whole-Tree Decline
As the disease progresses, the tree’s canopy thins out. Branches may yellow in a pattern that affects one section of the tree first rather than the whole tree uniformly. This lopsided thinning, sometimes called “yellow shoots,” can be visible from a distance. Eventually the entire canopy becomes sparse, with dieback on multiple limbs.
What makes this especially frustrating is the timeline underground. Root systems lose 30% to 50% of their mass in the early phases of infection, well before the canopy shows obvious decline. By the time the tree looks clearly unhealthy from across the grove, more than 70% of the roots are already gone. The visible symptoms you notice above ground are essentially the late stages of a problem that started much earlier below the soil line.
Spotting the Insect That Spreads It
Citrus greening is spread by the Asian citrus psyllid, a tiny mottled-brown insect about 3 millimeters long, roughly the size of an aphid. The easiest way to identify it is its feeding posture: it tilts its body at a 45-degree angle with its head pressed against the leaf and its tail end raised in the air. No other citrus pest feeds in this position.
Females lay small, yellow-orange, almond-shaped eggs tucked into the folds of new growth, the soft unfurling leaves sometimes called “feather flush.” The nymphs are yellow-orange (sometimes greenish) and tend to cluster on stems near where leaves attach. Older nymphs are easier to spot because they’re bigger, have visible wing buds and red eyes, and produce white waxy tubes that stick out from their bodies. These waxy secretions often attract ants or lead to sooty mold on the leaves, which is another indirect visual sign that psyllids are present.
What to Look For First
If you’re inspecting a citrus tree and wondering whether it has greening, start with the leaves. Look for yellow blotches that don’t match on either side of the midrib. Check new growth for psyllid eggs or nymphs. Then look at the fruit: lopsided shape, uneven coloring, and bitter taste are strong indicators. A single symptom alone isn’t definitive, since other conditions can mimic individual signs. But asymmetric leaf mottle combined with misshapen, partially green fruit on a thinning tree is a pattern that points clearly toward HLB.