Brown Spots on Lemons: Why They Appear and What to Do

Brown spots on lemons stem from at least half a dozen distinct causes, ranging from fungal infections and cold-storage damage to tiny mites you can barely see. Some spots are purely cosmetic and the fruit underneath is perfectly fine; others signal decay that can spread fast. Telling the difference matters both for your grocery choices and for anyone growing a lemon tree, because each cause has its own fix.

Fungal Infections Are the Most Common Culprit

Two fungal diseases account for a large share of brown spots on lemons, especially in humid or rainy climates. The first is brown rot, caused by species of Phytophthora, a water mold that thrives when rainfall is heavy. Brown rot typically starts as a firm, leathery brown patch that can expand rapidly across the rind, often giving off a faintly sour or fermented smell. It causes serious economic losses in lemon-growing regions during wet seasons.¹ If you see a soft, spreading brown area on a lemon, brown rot is a strong possibility, and the fruit should be discarded because the decay usually extends well below the surface.

The second common fungal disease is anthracnose, caused by Colletotrichum species. Anthracnose spots tend to be darker and more sunken than brown rot patches, sometimes appearing as small, round, depressed lesions that may develop tiny dark spore-producing structures in their centers. Lab studies have confirmed that the fungus can produce typical anthracnose symptoms on lemons within about five days under warm conditions.² Trees that are stressed by drought, poor nutrition, or other diseases are more vulnerable. On a single lemon sitting on your counter, anthracnose spots usually mean the fruit is past its prime and headed for the compost bin.

Citrus Canker Leaves Raised, Crater-Like Marks

Not all brown marks on lemons are flat discolorations. Citrus canker, caused by the bacterium Xanthomonas citri, produces raised, callus-like outgrowths on leaves, stems, and fruit. The spots often have a characteristic “target” look: a raised corky center ringed by a yellow halo. On fruit, these lesions feel rough and bumpy rather than soft or sunken. Surveys in citrus-growing areas have documented canker symptoms on lemons, grapefruit, oranges, and other citrus species.³

For home growers, citrus canker is a significant concern because the bacterium spreads easily through wind-driven rain, contaminated tools, and even people brushing against wet foliage. Many citrus-producing regions have strict quarantine and reporting rules for canker. The good news for shoppers is that canker-affected fruit, while ugly, is not a food safety risk. The interior of the lemon is usually unaffected, and the spots are superficial. Commercial packers almost always cull these fruits before they reach the store, but if you grow your own lemons, you might encounter them regularly during outbreaks.

Cold Storage and Chilling Injury

If you have ever pulled a lemon from the back of your refrigerator and found pitted, brown-stained patches on the rind, you were likely looking at chilling injury. Lemons are subtropical fruit and their rind cells can be damaged by prolonged exposure to cold temperatures. Research on Eureka lemons has shown that chilling injury symptoms appear when fruit is stored below about 13 °C (roughly 55 °F), which is considerably warmer than a typical home refrigerator set to around 3–5 °C.⁴

The symptoms fall into a few recognizable patterns: pitting, where small depressions form in the rind surface; membranous staining, where patches of the rind take on a brown, waterlogged appearance; and browning of the white pith beneath the peel.⁴ These changes are cosmetic in the early stages, and chilling-injured lemons often still taste fine once you cut them open. But severely affected fruit can develop off-flavors and dry out more quickly, so it is worth checking the flesh before juicing.

The practical tension here is obvious: refrigeration extends a lemon’s shelf life by slowing microbial growth, yet it can also cause chilling damage. One study tracking home storage conditions found that lemons held under refrigeration showed little to no spoilage damage even after 28 days, suggesting that for most people, the trade-off still favors keeping lemons in the fridge.⁵ If you go through lemons quickly, leaving them on the counter at room temperature avoids chilling injury entirely. If you buy a large bag and want them to last, the fridge is still the better bet, accepting that some cosmetic pitting may develop on fruit stored for several weeks.

Oleocellosis and Other Mechanical Damage

Lemons have a rind packed with tiny oil glands. When the fruit is squeezed, dropped, or roughly handled, the thin skin over those glands can rupture, releasing the essential oil into the surrounding rind tissue. That oil is phytotoxic to the rind’s own cells, and the resulting damage shows up as dark, sunken blemishes that can develop within just a few days of the injury. This condition is called oleocellosis, and it has been studied in detail on navel oranges, where researchers found that released surface oil infiltrates the rind through the broken epidermis, rapidly breaking down the underlying cells and causing the characteristic collapse and darkening of the tissue.⁶

Lemons are just as susceptible. The spots from oleocellosis tend to appear within a day or two of the damage event, and they are irregular in shape, often following the outline of wherever the fruit was pressed or bumped. Unlike fungal spots, oleocellosis patches are dry and firm rather than soft or mushy. The fruit inside is almost always perfectly normal. If you notice dark blotches forming shortly after you bring lemons home from the store, rough handling during transport is the most likely explanation. Storing lemons in a single layer rather than piled together, and avoiding dropping them into a bag from a height, helps prevent this kind of cosmetic damage.

Mite and Insect Scars

Two groups of tiny arthropods commonly leave brown marks on citrus fruit. Citrus rust mites feed on the outer cells of the rind. When they attack lemons during the fruit’s early growth phase, the dead epidermal cells oxidize and crack as the fruit expands, producing a rough, brownish-black surface texture sometimes called “russet.”⁷ Russeted lemons look dull and rough instead of bright and glossy, but the damage is entirely superficial. The juice, flesh, and zest beneath the discolored layer are unaffected.

Citrus thrips are another pest that leaves scarring. Thrips feed on the young fruit surface shortly after the petals drop, creating silvery or brownish scab-like marks, especially around the stem end. Studies in California citrus orchards have documented significant scarring from thrips across different citrus species, with some species like sweet oranges being more affected than others.⁸ As with rust mite damage, thrips scars are cosmetic. Commercially, heavily scarred fruit gets diverted from the fresh market to juice production, which is one reason supermarket lemons tend to look spotless while backyard lemons often wear a few blemishes.

If you grow your own lemon trees and notice these kinds of rough or scabby marks spreading across developing fruit, pest management during the flowering and early fruit-set stage is when intervention matters most. By the time scars are visible on a mature fruit, the damage is done and cannot be reversed.

Enzymatic Browning After Cutting

A different type of brown discoloration appears after you slice into a lemon. Cut surfaces can darken over the course of hours, driven by enzymes called polyphenol oxidases (PPOs) that react with oxygen in the air and naturally occurring phenolic compounds in the fruit tissue. This is the same family of reactions that turns a cut apple brown or a peeled banana dingy. In fruits and vegetables broadly, enzymatic browning from PPOs is one of the main factors affecting the color quality of cut produce.⁹

Lemons actually resist this type of browning better than many fruits because their high acidity slows PPO activity. That said, if you leave a cut lemon on the counter for several hours, some surface darkening is normal. The fruit is still safe to use. Wrapping the cut face tightly or placing it cut-side down on a plate in the fridge slows the process considerably. Adding a bit of lemon juice to other cut fruits to prevent browning is a well-known kitchen trick, and it works precisely because the citric acid lowers the pH enough to inhibit those same enzymes.

How to Decide Whether a Spotted Lemon Is Still Good

The brown spots you encounter in everyday life fall into two broad categories: those that stay on the surface and those that penetrate into the flesh. Knowing which is which saves you from wasting good fruit or, less commonly, eating something genuinely spoiled.

Firm, dry, superficial marks: Oleocellosis patches, pest scars, minor chilling pits, and canker lesions are all surface-level. The rind may look ugly, but if you cut into the fruit and the flesh is pale, juicy, and smells normal, it is perfectly fine to eat or juice.
Soft, spreading, or foul-smelling spots: Brown rot and advanced anthracnose produce soft, expanding patches that may smell off. The decay usually extends into the flesh. Discard the entire fruit, because trimming around the spot is unreliable with these fast-moving infections.
Brownish water-soaked patches after refrigeration: Chilling injury is cosmetic in mild cases. If the underlying flesh looks normal once you peel back the damaged rind, the lemon is usable. If the pith has turned brown and the fruit feels dry or mushy inside, toss it.

When in doubt, trust your nose. A healthy lemon smells sharply citrusy. Off odors, fermented or musty smells, or any sign of mold growing on or near the brown spots all mean the fruit has turned.

Storage Tips That Actually Help

Preventing brown spots at home mostly comes down to managing temperature, moisture, and physical damage. For whole lemons you plan to use within a week, a countertop fruit bowl at room temperature is fine and avoids any risk of chilling injury. For longer storage, the refrigerator dramatically extends shelf life. Lemons kept in refrigerated conditions showed minimal spoilage even approaching a month of storage in one recent study.⁵

A few habits make a real difference. Storing lemons in a sealed plastic bag or airtight container in the crisper drawer limits moisture loss and reduces the pitting associated with chilling injury, because the humidity inside the bag stays higher than in the open fridge. Keeping lemons in a single layer rather than stacked prevents the pressure bruising that triggers oleocellosis. And checking your stored lemons every few days lets you remove any fruit that is starting to mold before it spreads to its neighbors.

For home growers, the window between harvest and storage matters. Fruit picked while wet from rain or irrigation is more susceptible to fungal infections, including brown rot. Letting lemons dry on the tree or at least air-drying them before storing helps keep Phytophthora and other moisture-loving pathogens at bay.

Why Store-Bought Lemons Look So Perfect

If you have ever compared the blemish-free lemons in a supermarket bin with the mottled fruit on a backyard tree, the gap can seem absurd. Commercial citrus goes through a packing line that washes, waxes, and grades every piece of fruit. Lemons with significant scarring, canker marks, or cosmetic blemishes get sorted out by optical grading equipment and diverted to juice processing. The wax coating applied to the remaining fruit slows moisture loss and gives that uniform glossy sheen, but it also masks minor surface imperfections.

None of this means a blemished lemon is inferior on the inside. The grading is almost entirely about appearance, not flavor or nutritional content. A russeted lemon from a tree with rust mites or a lemon with a few oleocellosis patches from rough handling will yield just as much juice as its flawless-looking supermarket twin. Farmers’ market shoppers and home growers learn this quickly, but for anyone used to buying only the prettiest fruit, it can be a revelation that spots and scars are just part of what citrus looks like when it has not been beauty-pageant curated.

When Brown Spots on Lemon Trees Signal a Bigger Problem

If you are seeing brown spots not just on the fruit but also on the leaves and twigs of a lemon tree, the list of possible causes narrows. Citrus canker produces matching lesions on leaves, stems, and fruit simultaneously, making it one of the easiest diseases to identify visually. Anthracnose also attacks leaves and twigs, causing twig dieback and leaf spots that can weaken the tree over successive seasons. Brown rot tends to stay on the lower canopy and fruit closest to the ground, because the Phytophthora spores splash up from the soil during rain.

For backyard trees, good air circulation through selective pruning, removing fallen fruit and leaf litter from around the base, and avoiding overhead watering all reduce infection pressure from both bacterial and fungal pathogens. Copper-based sprays remain a standard preventive treatment for canker and anthracnose in home orchards, though they work best as a preventive measure applied before symptoms appear rather than as a cure for existing infections. If brown rot is a recurring problem, keeping fruit off the ground with stakes or picking fruit promptly after rain reduces contact with splash-borne spores. Potassium phosphite has also shown effectiveness against Phytophthora brown rot when applied both before and after harvest.¹

Rust mite populations tend to build up in hot, dry weather and can be managed with sulfur sprays or miticide applications timed to early fruit development, which is when the feeding damage that causes russet occurs.⁷ If you only notice the rough, dark rind after the fruit has matured, the damage happened months earlier and there is nothing to do for that particular crop. The intervention point is the following season, during bloom and early fruit set.

1
European Journal of Plant Pathology. Control of Phytophthora brown rot of lemons by pre- and postharvest applications of potassium phosphite
2
ResearchOnline@JCU. Detection and biological control measures of anthracnose causing fungus isolated from Citrus limon (L.)
3
Pakistan Journal of Agricultural Sciences. First report of Xanthomonas citri Subsp. Citri causing citrus canker on grape fruit (Citrus paradisi), washington naval (Citrus sinensis), kaghzi limon (Citrus aurantifolia Swingle), lemon (Citrus lim
4
Acta Horticulturae. INFLUENCE OF HARVEST SEASON, FRUIT MATURITY AND STORAGE TEMPERATURE ON THE DEVELOPMENT OF CHILLING INJURY IN ‘EUREKA’ LEMON FRUIT
5
LWT. Keep it cool and clean: Impact of home storage practices on fresh fruit and vegetable spoilage and efficacy of chemical versus green disinfectants
6
PubMed Central. Structural basis of the rind disorder oleocellosis in Washington navel orange (Citrus sinensis L. Osbeck)
7
ScienceDirect. Eriophyoid Mites Their Biology, Natural Enemies and Control – Section: Damage and control of eriophyoid mites in crops 3.2.1 Stylar feeding injury and control of eriophyoid mites in citrus
8
Oxford Academic. Differential Impacts of Citrus Thrips Across Sweet Orange and Mandarin Species
9
PubMed Central. Recent Trends in Controlling the Enzymatic Browning of Fruit and Vegetable Products