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

Brown spots on a lemon are usually a problem with the peel, not the fruit inside. The peel is packed with tiny oil glands that bruise easily, and bruised oil turns brown. A smaller group of spots are the first sign of a fungus working its way into the fruit. So the useful question is whether the spot sits on the surface or goes deeper, not whether it is brown.

Is a Lemon With Brown Spots Safe to Use

Scabby, brown to silvery scarring from tiny insects called thrips doesn’t harm the flavor or the inside of the fruit.1UC Statewide IPM Program. Thrips Spots from bruised oil glands or mild cold damage also stay in the outer peel. Cutting the lemon open is a reliable check: if the flesh and juice look and smell normal, use it.

At the cutting board, press the spot first. Firm means peel damage, while soft or mushy suggests rot. Look for fuzz or white or green growth on or near the spot, and sniff for a sour, musty or fermented smell instead of fresh citrus. Then slice near the stem end, where hidden rot often starts. Wash the lemon before cutting so surface dirt isn’t dragged into the flesh.

Zest comes from the peel, so skip any scarred or spotted area. A scarred lemon is fine for juice, so save the cleaner-looking ones for zesting. If a spot is flat and firm but the lemon feels slightly lighter or softer overall, cut it open before deciding, since the whole fruit may be drying out even when the spot is just a scar.

Mold on a lemon reaches deeper than you can see, so don’t cut it off. Discard any moldy lemon.2This Healthy Table. How to Tell if Lemon Has Gone Bad A lemon can also rot inside with no outside sign, browning from the stem or tip end along the center.3Physiological and Molecular Plant Pathology. Alternaria alternata causing inner black rot of lemon (Citrus limon) fruits in Turkey: Genetic diversity and characterisation In one large check, about 1 in 7 lemons with clean skins had blackened insides.4Physiological and Molecular Plant Pathology. Alternaria alternata causing inner black rot of lemon (Citrus limon) fruits in Turkey: Genetic diversity and characterisation Brown or black flesh near the stem end means discard it, even if the skin looked fine. Throw out a lemon with even one off area in the flesh rather than trimming around it, since rot can extend past what you can see.

How to Tell What Caused the Spots

Septoria often leaves tearstaining, a runny streak of discoloring down the peel.12UC IPM. Diseases and Disorders of Fruit Its pits can show tiny black dots inside them.13NSW Department of Primary Industries. Septoria spot in citrus Septoria spots also stand out much more once the lemon turns yellow.14UC IPM. Diseases and Disorders of Fruit

Where the spots sit on the tree is one clue among several. Spots mostly on low fruit near the ground suggest splash-borne brown rot. Spots on the sunny side suggest sunburn, which can then invite anthracnose. Scarring in a ring near the stem fits insect feeding on young fruit. Spots only on stored lemons point to cold or handling damage.

It’s easy to assume every dark spot is disease. Many dark marks are old scars from when the fruit was tiny. Scars stop growing, while disease spots grow or multiply over days. Mark a spot with a pen and check in a week.

Several of these problems look alike at a glance, especially anthracnose, Septoria and citrus black spot, so a confident name from appearance alone is often a best guess. If you’re a gardener and the spotting returns every year or covers much of the crop, a local extension office or nursery can examine a sample fruit and give a firm identification before you spend money on sprays.

Bruised Oil Glands and Other Peel Damage

Overnight, lemons fill with water and are tight by morning, which puts pressure on their oil glands.15Proceedings of the Florida State Horticultural Society. A Method to Predict the Post-Harvest Incidence of Oleocellosis on Lemons In early morning the glands rupture easily from bumps or squeezing.16Proceedings of the Florida State Horticultural Society. A Method to Predict the Post-Harvest Incidence of Oleocellosis on Lemons As the day warms and the fruit loses water, the pressure eases and the glands are less likely to burst.17Proceedings of the Florida State Horticultural Society. A Method to Predict the Post-Harvest Incidence of Oleocellosis on Lemons So pick lemons later in the day, once dew dries, and handle them gently.

Burst oil glands start as greenish or brown patches where the fruit was pressed or dropped. Crushed oil escapes slowly and reacts with air, so the color often takes a day or two to show, sometimes after picking or bagging. A spot found in the fruit bowl may therefore come from handling at picking or at the store, not from anything on the tree. The damage stays in the peel and doesn’t soften the fruit, so it’s cosmetic and doesn’t mean the tree needs treatment.

To bruise fewer lemons, wait until the fruit and leaves are dry from dew or rain and the lemons have lost some of their overnight water. Clip or twist each lemon off gently rather than yanking it, because pulling can tear the peel at the stem end and make a wound. Place lemons into a shallow container or basket one at a time instead of dropping them into a deep pile, where the weight of the top ones presses on those below.

Cold damage works through the same glands. The darkening of cold-damaged citrus comes from oil leaking from glands and turning brown.18Postharvest Physiological Disorders in Fruits and Vegetables. Citrus Lemons held near 2°C (36°F) developed cold injury and small sunken spots later.19Acta Horticulturae. Sustainable postharvest treatments to control chilling injury, peteca and Penicillium spp. on Verna lemons High humidity in storage reduces peel drying, shriveling, cold injury and decay in lemons.20Elsevier / Scientia Horticulturae. Effects of high-humidity storage on quality, decay and storage life of cherry, lemon and peach fruits

Peel damage often starts early. The first 8 to 12 weeks after fruit set are the most critical time for blemishes.21International Journal of Agriculture and Biology. Biotic and Abiotic Factors Causing Rind Blemishes in Citrus and Management Strategies to Improve the Cosmetic Quality of Fruits

Fungal Rots That Spread

Brown rot is caused by a water mold that also attacks roots, bark and trunk, causing oozing gum.22TÜBİTAK Academic Journals. Phytophthora-citrus interactions and management strategies: a review Fruit near the ground gets infected when rain splashes soil onto it.

Alternaria fungi can rot lemons from the stem or tip inward.23Physiological and Molecular Plant Pathology. Alternaria alternata causing inner black rot of lemon (Citrus limon) fruits in Turkey: Genetic diversity and characterisation Alternaria has caused severe outbreaks of rot on lemons in orchards.24Physiological and Molecular Plant Pathology. Isolation and characterization of pathogen causing brown rot in lemon and its control by using ecofriendly botanicals Alternaria brown spot has also spread to some newer lemon varieties that used to resist it.25Phytopathologia Mediterranea. Alternaria brown spot on new clones of sweet orange and lemon in Italy

Anthracnose spores sit dormant on the peel until the fruit is injured.26idtools.org. Brown Spots on Lemons: Why They Appear and What to Do Lemons already hurt by sunburn, insects, bruising or long storage are most likely to show it.27idtools.org. Brown Spots on Lemons: Why They Appear and What to Do Septoria infects in wet weather and often doesn’t show until lemons are in storage.28UC IPM. Diseases and Disorders of Fruit A wound such as a thrips scar, a crack, a scrape or a sunburned patch gives a fungus an easy way past the peel’s protective surface.

Wet weather gives these fungi their chance. Spores need a film of water on the fruit or leaves to germinate, so long periods of rain, heavy dew or sprinkler spray raise the risk. Rain also carries spores from fallen leaves, dead twigs and old fruit up to healthy fruit, which is why a tidy tree base matters. Dry spells slow these fungi, so spotting often follows a wet autumn or winter and then eases in summer.

If you find a rotting lemon on the tree, pick it off and throw it in the trash or green waste bin rather than leaving it on the ground, where it keeps releasing spores. Avoid a home compost pile that may not get hot enough to kill the fungi. If you handled several rotting fruits, wash your hands and any clippers afterward so you don’t carry spores to healthy ones.

How to Prevent Brown Spots on Your Tree

Brown rot is managed mainly by prevention.29UC IPM. Brown Spots on Lemons: Why They Appear and What to Do Prune lower branches to at least 24 inches above the ground.30UC IPM. Brown Spots on Lemons: Why They Appear and What to Do Then spray copper fungicide once before or just after the first autumn rain.31UC IPM. Brown Spots on Lemons: Why They Appear and What to Do Repeat in late winter if rainfall is heavy, covering branches up to about 4 feet.32UC IPM. Brown Spots on Lemons: Why They Appear and What to Do

For a copper spray at home, use a product labeled for citrus and follow the label rate. Spray on a dry, still day so it can dry on the leaves, and wear gloves and eye protection. Cover the lower canopy and fruit, where splash infection happens.

Since anthracnose needs an injury to take hold, protecting fruit from sunburn and pests cuts spotting. Prune enough to let air move through the canopy, but leave enough leaves to shade developing fruit from strong afternoon sun. Avoid heavy pruning in hot weather, which suddenly exposes fruit that had been shaded. Check young fruit and new growth for tiny thrips early in the season, since scarring happens when the fruit is small, and ask a nursery about options labeled for citrus if the problem is heavy.

Pick up fallen and rotting fruit so spores don’t build up. During the rainy season, rake up fallen leaves and twigs under the canopy, because they harbor spores that can splash back onto fruit. Remove dead or diseased branches with clean pruning tools, cutting back into healthy wood, so the tree has fewer places to hold moisture.

Storing Lemons So They Stay Spot-Free

Cold storage is the main way to make citrus last longer.33Postharvest Physiological Disorders in Fruits and Vegetables. Citrus But very cold storage near 2°C led to cold spots on lemons later.34Acta Horticulturae. Sustainable postharvest treatments to control chilling injury, peteca and Penicillium spp. on Verna lemons Keep lemons in the crisper drawer rather than against the back wall of the fridge. Keeping them humid, such as in a lidded container or bag, slows drying and spotting.35Elsevier / Scientia Horticulturae. Effects of high-humidity storage on quality, decay and storage life of cherry, lemon and peach fruits

Line the container with a paper towel if you see condensation, since standing water on the peel invites mold. Keep lemons apart from fruit that is already rotting, and avoid stacking them tightly so air can reach each one. On the counter lemons last about a week, and in the fridge drawer they keep several weeks.

Watch for a peel that goes dull, shriveled or hard as it dries. Soft patches mean rot has begun, and blue-green or white fuzz means discard. One rotting lemon can spread mold to its neighbors.

Why Cut Lemons Turn Brown

Citric acid and vitamin C in lemon juice slow browning, which is why cooks use lemon on apples.36PubMed Central. Recent Trends in Controlling the Enzymatic Browning of Fruit and Vegetable Products That protection fades over time as those acids are used up.37PubMed Central. Recent Trends in Controlling the Enzymatic Browning of Fruit and Vegetable Products Cut lemon kept cold holds its aroma and quality longer.38International Journal of Food Properties. Quality of fresh cut lemon during different temperature as affected by chitosan coating with clove oil So wrap a cut lemon face down and use it within a few days.

What you usually see on a cut lemon is the exposed surface drying and darkening. A lemon half left in the fridge may look dull or leathery before it looks truly brown.

A dry, darker cut face is usually drying, not spoilage. Slime, fuzz or a sour smell means throw it out. If the rest looks fresh, slice off a thin dried layer. Drying can concentrate the sour taste a little but is harmless.

Store the cut half face down on a small plate or in a covered container to limit air and drying. For longer storage, squeeze the juice into a clean jar and refrigerate it for a few days, or zest the peel of a whole lemon before cutting it.