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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Raised spots with yellow halos can point to citrus canker; corky, wart-like growth suggests citrus scab; greasy blisters under leaves are a clue to greasy spot; and peeling bark or gumming near the trunk base may indicate Phytophthora foot rot. These four diseases differ in where they affect a tree and what conditions favor them, so look at several symptoms together rather than diagnosing from yellowing or leaf loss alone.
Compare the symptoms first
| Disease | Where to look | Distinctive signs | Context |
|---|---|---|---|
| Citrus canker | Young leaves, shoots, and fruit | Raised brown circular or irregular lesions, often with yellow halos | Can spread in wind-driven rain and on contaminated people, animals, clothing, or equipment |
| Citrus scab | Young leaves, stems, and fruit | Corky, wart-like outgrowths and distortion | Florida guidance notes greater prevalence in the rainy season |
| Greasy spot | Leaves, especially the undersides | Yellow marks above; irregular brown, greasy-looking blisters below | Florida guidance associates it with rainy-season conditions |
| Phytophthora foot rot | Roots and trunk near the soil line | Peeling bark, gumming at wounds, chlorosis, or stem dieback | Soil-associated; drainage and trunk moisture matter |
These are useful diseases to recognize, not an official ranking by prevalence. UF/IFAS Extension describes lemon susceptibility and potential damage but does not provide comparative incidence figures. Its lemon-growing guide is specific to Florida home landscapes; seasonal timing and spray guidance below should not be treated as universal instructions.
1. Citrus canker: raised lesions with yellow halos
Citrus canker is a bacterial disease, and UF/IFAS describes lemon trees as highly susceptible. It can affect young leaves, shoots, and fruit. Small early spots can develop into raised brown lesions that are circular or irregular, commonly surrounded by yellow halos. A severe infection may cause defoliation and weaken the tree.
Wind-driven rain can spread the pathogen, as can contaminated equipment, clothing, animals, or people. Florida home-landscape advice includes planting in full sun, maintaining good air movement, and avoiding watering that wets foliage. The Florida guidance also discusses timely copper-based fungicide applications to newly emerging leaves to lessen impact. Copper is not a cure for every citrus problem: use a product only when its label permits the intended use, and follow current local rules. Florida canker status and regulations can change; the 2026–2027 UF/IFAS Florida Citrus Production Guide: Citrus Canker, released August 11, 2026, directs readers to current Florida authorities for status and rules.
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2. Citrus scab: corky, distorted growth
Scab is described by UF/IFAS as a major fruit disease of lemon. Young leaves, stems, and fruit are most susceptible. Look for corky outgrowths or wart-like formations, often accompanied by distorted or malformed foliage, stems, or fruit. This rough, raised growth differs from canker’s lesions, which are typically bordered by yellow halos.
The Florida home-landscape guide says scab is most prevalent during the rainy season and may be managed, when it is a problem, with one or two copper-based sprays during early fruit development. That is regional guidance, not a standard schedule for all climates or trees. Check with local extension and read the exact product label before considering any pesticide.
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3. Greasy spot: inspect both sides of the leaves
Greasy spot can severely affect lemon leaves. Early yellow marks appear on the upper surfaces; irregular brown blisters with a greasy appearance develop on the undersides and may later show on top. Defoliation can weaken the tree, so inspect both leaf surfaces when trying to distinguish this disease from other causes of yellowing or leaf loss.
UF/IFAS describes rainy-season prevalence in Florida. Its home-landscape guidance mentions one or two sprays of copper or copper plus horticultural oil; another home-landscape source emphasizes thorough coverage of leaf undersides. The 2026–2027 Florida Citrus Production Guide: Greasy Spot notes resistance in some fungal isolates to FRAC mode-of-action group 11 fungicides. Treatment choice and timing should therefore come from local extension guidance and the specific product label, not a generic spray recipe.
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4. Phytophthora foot rot: check the trunk at the soil line
Phytophthora foot rot affects roots and trunk tissue near the soil line. Signs can include peeling bark on crown roots or the trunk, gumming at damaged areas, yellowing leaves, stem dieback, and general decline; severe disease can kill a tree. Because the symptoms can overlap with other causes of decline, do not select a chemical treatment based on appearance alone.
Prevention guidance includes choosing a resistant rootstock, avoiding trunk injuries and trunk wetting, and keeping mulch away from the trunk base. Broader UF/IFAS citrus guidance also stresses good drainage, correct planting depth, and checking pathogen levels before treatment. The 2026–2027 Florida Citrus Production Guide: Phytophthora Foot Rot, Crown Rot, and Root Rot provides current production context; home gardeners should seek local advice suited to their site and tree.
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Other symptoms and look-alikes
Melanose can make rough spots
Melanose can produce small brown leaf spots that begin sunken and then become raised and rough, like sandpaper. Fruit may develop raised, irregular brown spots with pale halos. UF/IFAS says melanose is usually not a major disease on lemons and describes its management alongside greasy-spot foliar treatments. It is a possible look-alike, not one of the four higher-priority diseases selected here. See the 2026–2027 Florida Citrus Production Guide: Melanose for current Florida management context.
Yellow leaves and leaf drop are not diagnoses
Yellowing, dieback, and leaf loss can have more than one cause. UF/IFAS discusses citrus greening separately, with signs including blotchy yellowing, dieback, small lopsided fruit, and eventual decline. A photo or a single symptom cannot confirm which problem is present. If the tree is declining or symptoms do not fit clearly, contact a local extension office or plant diagnostic service. The UF/IFAS guide to citrus problems in the home landscape offers additional identification context.
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- Let our professionally formulated plant food help your citrus tree grow healthy, strong AND abundantly producing
- Super, super concentrated - A little goes a LONG way
- Dilute one teaspoon of product into one gallon of water and apply weekly along the drip line. For trees in their first season, use one teaspoon per week. For mature trees, use up to two teaspoons per week.
- For indoor / container trees, cut dosage in half or apply every other week
- Farmer's Secret brings the same scientifically backed formula development process farmers get to YOUR garden… get in on the secret!
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
