Lemon Tree Black Leaves: 7 Causes and How to Fix Each

Lemon tree black leaves fall into two groups. A black film that wipes off is sooty mold, a fungus that grows on the sticky honeydew of sap-sucking insects and does not infect the leaf itself. Black or dark marks that stay after you wipe point to a real problem in the leaf: greasy spot, cold damage, a fungal or bacterial spot disease, root trouble, or nutrient and salt injury.

This guide is built around what you see on the leaf. For each of the seven causes it gives the signs, a quick check and what to do next, with figures from university extension services and FAO. It also has charts on salt tolerance, leaf nutrient ranges and the temperatures that matter, and a calculator for the extra water needed to flush salt from the root zone. If your leaves are yellow rather than black, see our separate guide on why lemon tree leaves turn yellow.

Start with the wipe test

Take a damp cloth and wipe one black leaf. This one test splits the causes into two groups.

• The black comes off and the leaf is green underneath. This is sooty mold. Look for insects on the leaves and twigs above it, and for ants walking up the trunk.
• The black stays, or the leaf tissue itself is dark, blistered, sunken or dead. The leaf is damaged. Go to the symptom table below to narrow it down.

Next, note three things: where on the tree the damage is (new growth, old leaves, one branch, the whole tree), when it showed up (after a freeze, after rain, in summer heat) and whether the leaf feels sticky. These answers match the cause more often than the color does.

Lemon tree black leaves: match the symptom to the cause

Use this table as a first sorting step. Each row has its own section below with the source behind it.

1. Sooty mold: black film that wipes off

Sooty mold is a frequent reason a lemon tree looks black. It is a dark, thread-like fungal growth on the surface of leaves, twigs and fruit. The UC Statewide IPM Program explains that sooty mold does not infect the plant. It lives on honeydew, the sugary waste that sap-sucking insects drop as they feed. A thick coat still harms the tree because it blocks light, cuts photosynthesis and can make coated leaves age and fall early.

The black coat is a sign, not the disease. University of Florida extension notes that sooty mold signals insect numbers have reached damaging levels. On citrus the usual honeydew makers are soft scales (such as black scale and brown soft scale), aphids, mealybugs, whiteflies and the Asian citrus psyllid. Armored scales such as California red scale make no honeydew, so they do not cause sooty mold. Ants matter too: they feed on honeydew and guard the insects from their natural enemies.

How to check

• Look at the leaves and twigs directly above the black area. Honeydew falls down, so the insects are often one level higher.
• Turn leaves over and check new shoots for aphids, whitefly nymphs, mealybugs and scales on the twigs.
• Watch the trunk for a line of ants.
• Feel the leaves. Fresh honeydew is sticky.

What to do

• Control the insect first. Once honeydew stops, sooty mold fades over time. A strong stream of water knocks off many aphids.
• Stop the ants. A sticky barrier band on the trunk and trimming branches that touch walls or fences keep ants out of the canopy, so ladybugs and parasitic wasps can work. See our guide to aphid predators for the natural enemies.
• Clean the leaves gently. The RHS (UK) advises wiping leaves with lukewarm water and avoiding strong soaps or detergents, which can scorch foliage. Start with water alone, and if you must add soap, use only a little mild soap.
• Use oil with care. UF says oil sprays loosen sooty mold and help control the insects. University of Nevada, Reno extension warns not to use horticultural oils in temperatures in the 90s °F, on drought-stressed plants or new transplants, or in freezing weather.

For black scale in California, UC IPM says one well-timed oil spray against young scales is often enough, before they reach the hard adult stage. Fruit with sooty mold is still safe to eat after washing. Always follow the product label and local rules for any spray, including oils and soaps, and observe the label’s re-entry and pre-harvest intervals.

▶ Aphids, black spots and sooty mold on lemon trees, and how to keep citrus leaves healthy. · 10:52

2. Greasy spot: dark, raised blisters under the leaf

Greasy spot is a fungal disease caused by Zasmidium citri-griseum. Warm, humid nights and heavy summer rain, as in Florida, favor it. The first sign is a yellow spot on the top of the leaf. Below it, on the underside, an irregular brown blister forms that turns dark, slightly raised and greasy-looking. Unlike sooty mold, it does not wipe off. Leaves can drop even before the full symptoms show, and heavy leaf loss weakens the tree and makes it more prone to cold damage.

The Florida Citrus Production Guide chapter on greasy spot says spores come mainly from rotting leaf litter on the ground. Major spore releases usually happen from April to early June, and infection conditions last from June through September. Leaves stay susceptible all their lives, and symptoms take several months to appear. So the black blisters you see in winter often come from infections the summer before.

What to do

• Home trees: rake up and remove fallen leaves under the tree, keep the tree well fed and watered, and accept light spotting on older leaves.
• Commercial groves: the Florida guide gives one spray of oil (5 to 10 gal/acre) or copper plus oil from mid-May to June for processing Valencias, and says about 2 lb of metallic copper per acre usually gives adequate control. Copper gives more consistent control than oil alone. Some groves need a second spray after the summer flush.
• Coverage matters: the spray has to reach the underside of the leaves, where the fungus enters.

Copper can spot fruit in hot weather. The same guide says summer copper sprays should go on only when temperatures are below 94°F, at no more than 2 lb metallic copper per acre and without oil. Rates are for Florida groves; follow the label and local extension advice where you farm.

3. Cold damage: new growth turns black after a freeze

If the black leaves appeared a day or two after a cold night, think frost first. A UGA Cooperative Extension bulletin on freeze injury explains that citrus can be injured below about 28°F (−2.2°C), although trees that have had weeks of cool weather can survive colder nights. After a hard freeze, hardened-off leaves turn brown, while tender new leaves turn black. Lemons and limes are the least cold-hardy citrus, behind satsumas, mandarins, sweet oranges and grapefruit.

UF/IFAS describes the early sign as dark, water-soaked areas on the leaf. Frozen new growth often turns blackish when it thaws. Leaves that drop within a few days usually mean the wood survived. Leaves that stay stuck on dead twigs often mean the wood was killed.

What to do

• Check the wood. Scrape the bark with a thumbnail. Green tissue is alive; tan or brown tissue is dead.
• Do not prune right away. Dieback can keep moving for weeks. UGA advises waiting and pruning to live wood in late spring or early summer.
• Hold back fertilizer and water. Feeding too early can push tender growth that the next frost will kill, and a tree with fewer leaves uses less water.
• Protect potted lemons. In the UK, the RHS says citrus will not reliably survive winters outdoors and should spend winter in a greenhouse, conservatory or glazed porch.

Chart

Temperatures that matter for lemon leaves

°F; thresholds named by US extension services

4. Fungal and bacterial spots that stay on the leaf

Several spot diseases leave dark marks that do not wipe off. They are harder to tell apart by eye, and some are regulated, so a lab diagnosis is worth getting if you see them on many leaves or on fruit.

• Citrus black spot (Phyllosticta citricarpa) is mainly a fruit disease, with hard, sunken spots that have gray centers and brick-red to black margins. The Florida guide on citrus black spot says leaf symptoms are few, but the spores form in fallen leaves. It notes lemons are reported to be even more susceptible than sweet oranges in other regions. Parts of Florida are under quarantine, with rules on moving fruit and leaf litter.
• Alternaria brown spot causes brown spots or blotches with yellow areas around them. UF notes a useful sign: leaf veins blacken as they lead away from the dark lesions. It is most severe on some tangelos and tangerines, such as Minneola and Dancy.
• Anthracnose mostly attacks weakened twigs. UC IPM says dying leaves and twigs become covered with dark spores, the disease is most common in long wet springs, and it mainly affects stressed trees with old, dead wood.
• Septoria spot can spot leaves and twigs that frost or pests have already weakened, mostly in cool, moist weather in California. UC IPM notes it can be confused with copper injury.
• Citrus canker is bacterial. UF describes raised, corky lesions with a water-soaked margin and a yellow halo, visible on both sides of the leaf. It spreads fast with wind-driven rain, and Florida has a statewide canker quarantine.

Mites can also darken citrus. UF notes that rust mites turn the skin of young fruit brownish-black and rusty, and on some varieties damage stems and leaves enough to cause leaf drop. Our page on citrus red mite control covers the options.

What to do: remove dead twigs and fallen leaves, keep the canopy open so leaves dry quickly, and use clean nursery trees. If you suspect black spot or canker in the US, contact your county extension office or state agriculture department before moving fruit or plant material. Fungicide choice and timing depend on the disease, so follow the product label and local rules.

5. Root rot and Phytophthora: pale leaves, dark bark

Root rot rarely turns leaves black. It shows up first as pale, light green or yellow leaves, leaf drop and slow decline, because the roots can no longer take up water and nutrients. The UC IPM page on Phytophthora root rot in citrus says the fungus-like pathogen destroys feeder roots, and the symptoms are hard to tell from nematode, salt or flooding damage. Only a lab test can confirm it.

The dark part is often on the trunk. UF describes foot rot as peeling bark at the soil line, sometimes with reddish-brown gum oozing out. When the trunk is partly girdled, the leaves can show yellow veins, and the tree declines.

What to do

• Improve drainage and avoid overwatering. Water in the morning so the bark dries.
• Keep the bud union well above the soil, and keep mulch and grass away from the trunk.
• Dig near the drip line and check the feeder roots. Healthy roots are firm; rotted ones are soft and the outer layer slips off.
• For orchards, UC IPM says counts above 15 to 20 propagules per gram of root-zone soil may justify a treatment. Send composite samples to a lab within 24 to 48 hours.
• For potted lemons, the RHS warns that overwatering in winter is a common problem. Never leave pots standing in water.

6. Nutrient problems: patterned or bronzed leaves

Nutrient shortages usually yellow citrus leaves rather than blacken them, but they make trees weaker against the other causes, and some excesses burn leaf tissue dark. UF/IFAS describes magnesium deficiency as yellow blotches near the midrib that can end up bronze, and says leaves that have lost most of their color drop freely in cold or dry weather. Iron and manganese shortages show as pale leaves with green veins.

The reliable way to know is a leaf test. The Florida guide on citrus nutrition recommends sampling about 100 spring-flush leaves, 4 to 6 months old, from 15 to 20 similar trees, usually in July and August. It also says soil pH between 5.5 and 6.5 helps avoid many shortages.

• Send leaves from non-fruiting twigs and leave out damaged or diseased leaves.
• Compare the results with the optimum ranges in the chart.
• Correct one nutrient at a time and test again the next year.

Follow the fertilizer label and local rules on nutrient use, and ask your extension service or a certified crop adviser to read the leaf test with you.

Chart

Optimum leaf nutrient ranges for citrus

% of leaf dry weight, 4- to 6-month-old spring-flush leaves from non-fruiting twigs

7. Salt and fertilizer burn: dark, dead leaf edges

FAO notes that sodium or chloride toxicity usually shows as leaf burn on the leaf edges, and that a leaf analysis for chloride and sodium confirms it. Citrus is sensitive. FAO salt tolerance data rate lemon as sensitive, with yield starting to fall when the average root-zone salinity passes 1.5 dS/m and dropping about 12.8% for each extra dS/m. The Florida nutrition guide adds that leaf burn and leaf drop can occur when leaf chloride passes 1.0%.

Chart

Expected citrus yield as root-zone salinity rises

% of full yield vs average soil salinity (ECe, dS/m); calculated from FAO threshold and slope values

Salt builds up when irrigation water is salty, when too much fertilizer is applied, or when rain and watering never push water below the roots. Potted trees are at extra risk because the salts have nowhere to go.

What to do

• Test your irrigation water for salinity (EC) and chloride.
• Water deeply so some water drains below the root zone. FAO calls this extra the leaching requirement and gives a simple formula for it, which the calculator below uses.
• Avoid wetting the leaves with salty water. FAO warns that sprinklers can cause leaf burn when sodium or chloride concentrate on leaves, and that watering at night, when humidity is higher, often reduces the problem.
• Split fertilizer into smaller doses.
• For pots, water until it runs out of the bottom, and repot with fresh mix when roots fill the pot.

Try the numbers for your own farm below.

Look-alikes: yellow, blotchy or mined leaves

Some lemon leaf problems get mixed up with black leaves but need a different fix.

• Citrus leafminer: UC IPM describes shallow, winding tunnels in young leaves, with rolled and twisted shoots. On mature backyard trees it rarely causes serious damage.
• Huanglongbing (citrus greening): UF describes yellowing along the veins and a blotchy mottle on normal-sized leaves. There is no cure. UC IPM asks California residents to report suspect trees to the county agricultural commissioner, because quarantines apply.
• Spray burn: oil or copper applied in heat can scorch leaves and fruit. UF lists spray burn among the causes of twig dieback.

▶ Citrus greening: the leaf symptoms, the role of the Asian citrus psyllid and control options. · 13:17

How to diagnose lemon tree black leaves step by step

Work through these steps in order and stop when the cause is clear.

1. Wipe a leaf. If the black comes off, treat it as sooty mold and find the insect.
2. Think back over the last two weeks. A freeze points to cold damage; long warm, wet spells point to fungal spots.
3. Look under the leaves and on the fruit. Blisters, halos and sunken spots narrow down the disease.
4. Check the roots, trunk base and drainage if the whole tree is pale or dropping leaves.
5. Test water, soil and leaves if leaf edges are burnt or the pattern looks nutritional.
6. Send samples to a diagnostic lab when the spots stay unclear, especially in quarantine areas.

Scouting black leaves across a lemon orchard

In a backyard you can check every tree. In an orchard, problems such as sooty mold, frost damage and root rot often start in patches, so the task is finding the right blocks to walk. The same seven causes apply at orchard scale; what changes is how you find them. If you are planning a new block, our guide on how to plan a lemon orchard covers site, drainage and spacing choices that reduce many of the problems above.

Satellite vegetation maps can show which parts of an orchard are losing canopy vigor compared with the rest. They do not name the cause. The Farmonaut Satellite + AI Farm Monitoring System gives these maps through the season, which helps you choose where to walk and sample first. The checks in this guide still decide what is wrong.

Related pages on our site: farm management app for large holdings, satellite data API and API developer docs, product traceability, fleet management, carbon footprint tracking and crop loan and insurance verification.

▶ How satellite NDVI maps show crop stress across a farm before it is easy to see on the ground. · 4:09

How we checked the facts

We used extension and government sources only: the UC Statewide IPM Program (California), the 2026 to 2029 Florida Citrus Production Guide and other UF/IFAS publications, UGA Cooperative Extension, the University of Nevada, Reno, the RHS (UK) and FAO salt tolerance data. Rates and timings from Florida and California are local. Check with your own extension service before you spray, and always follow the product label and local rules. We removed percentage shares of “cases” for each cause from an earlier version of this page because no source supports them.

If this topic matters to you, read Black Dots on Tomato Leaves: 7 Powerful Solutions next.

Related reading on this site: Lemon Tree Fungus: 7 Powerful Ways to Prevent Disease.

FAQ

Why are my lemon tree leaves turning black?

If the black wipes off, it is sooty mold growing on honeydew from insects such as scales, aphids, mealybugs or whiteflies. If it does not wipe off, the leaf is damaged, most often by greasy spot, a recent freeze, a spot disease or salt burn. Use the wipe test and the symptom table above.

Will sooty mold kill my lemon tree?

Not directly. It does not infect the leaf. A heavy coat blocks light and can make leaves drop early, and the insects behind it can weaken the tree. Control the insects and ants, and the mold fades.

Can black leaves on a lemon tree turn green again?

Leaves coated with sooty mold can be cleaned and keep working. Leaves killed by frost, disease or salt will not recover; the tree replaces them with new growth once you fix the cause.

Should I cut off black leaves?

Not straight away. For sooty mold, clean rather than cut. After frost, wait until new growth shows which wood is alive, then prune in late spring. For spot diseases, remove fallen leaves and dead twigs, which carry spores.

Is fruit from a tree with black leaves safe to eat?

Fruit coated with sooty mold is still edible after washing, according to UC IPM. The Florida guide says fruit with black spot that stays on the tree until ripe is still suitable for processing, but in quarantine areas you must follow the rules on moving fruit.