What's Eating Your Lemon?

Citrus x limon

Reviewed by Kiersten Rankel M.S.

Quick Answer

For lemon trees, the most likely culprits are scale insects (waxy bumps glued to thorny stems and leaf veins, the worst pest of all citrus) and spider mites (pale dust along leaf undersides, common on potted Lisbon and Eureka brought indoors for winter). Mealybugs lodge in leaf-petiole junctions and aphids swarm spring flush growth.

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What does the damage look like?

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Waxy bumps and shiny leaves

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Pale dust along leaf undersides

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White cottony tufts in leaf joints

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Curled, sticky new growth

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Squiggly silvery trails on new leaves

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Pests, ranked by impact

Brown soft scale (Coccus hesperidum) clustered on a plant stem

Scale insects

Damage

High

Removal

Hard

What it looks like

Flat or domed brown, gray, or tan bumps cemented to leaf undersides, twigs, and around the base of thorns on Lisbon stems. 1 to 4 mm wide. Don't budge when touched. Often the first sign is a glossy film on broad oval leaves and the floor below the tree.

What the damage looks like

Sticky honeydew coats leaves and the pot or patio below. Black sooty mold grows on the residue. Yellow halos form around each colony, leaves drop early, and a heavy infestation knocks bloom and fruit yield down for the next season. Citrus is the scale magnet of the houseplant world, harder to clear than on most species.

How to get rid of them

Option 1

Brush and oil weekly for 4 weeks

Soak affected stems and leaf surfaces with horticultural oil (Bonide All Seasons, ~$15). Watch the thorns on Lisbon stems closely. Scale love the base of every spine.

Work each bump loose with a soft toothbrush. The oil weakens the wax shield and the bristles knock the body off.

Re-coat with oil and walk away. Repeat once a week for 4 weeks to catch every wave of crawlers as they emerge.

Option 2

Imidacloprid soil drench for ornamental indoor trees

Drench the soil with imidacloprid granules (Bonide Annual Tree & Shrub, ~$30). The systemic moves through sap and reaches scale where contact sprays can't. Skip this for any tree producing fruit you plan to eat or any tree flowering for outdoor pollinators. Use only on indoor ornamental lemons that are not bearing.

Option 3

Quarantine the tree at least 6 feet from other plants

Crawlers are the only mobile life stage and they can walk to any neighboring pot. Move the lemon away from other citrus, indoor tropicals, and herbs for the full 4-week treatment. Wipe down the surface where the pot sat. Reinfestation is the rule with scale, not the exception.

Common myth

Scale will fall off on its own once the tree gets stronger.

Scale stays attached for the rest of its life and lays eggs the whole time. Lemon trees almost never outgrow an active infestation. Without manual or chemical removal, populations build year over year and shut down fruit set.

Spider mites

Damage

High

Removal

Moderate

What it looks like

Almost too small to see. Yellow-green or red specks scattered along the underside of elongated oval lemon leaves and around the petiole-stem junction. Lisbon and Eureka are notoriously cold-sensitive, so most owners overwinter potted trees indoors. The dry forced-air heat is exactly what mites need to explode.

What the damage looks like

Tiny pale yellow flecks along the central vein at first, then a bronzed dusty look across the upper leaf surface. Fine silken webbing strung between the petiole and stem in serious infestations. Lemon leaves drop sooner than Meyer leaves under the same pressure because the foliage is slightly thinner. A bad winter outbreak can strip a tree before spring.

How to get rid of them

Option 1

Cool shower on the foliage, weekly for 3 weeks

Carry the pot to the shower or set it under a hose on a mild day. Spray cool water on every leaf underside for 30 seconds, working around the thorny inner branches carefully. Mites can't climb back fast and the lingering humidity slows survivors. Lemon foliage shrugs off a hard rinse. Repeat once a week for 3 weeks.

Option 2

Neem oil rotation, every 5 days for 3 rounds

Mix 2 tablespoons cold-pressed neem oil with 1 teaspoon dish soap per gallon of water.

Spray every leaf underside at lights-out, paying attention to where the petiole meets the stem. That's where mites cluster on lemon.

Repeat every 5 days for 3 rounds, covering one full egg-to-adult cycle.

Option 3

Park a humidifier near the indoor tree all winter

Run a small humidifier within 3 feet of the tree to hold relative humidity at 50 to 60% through the heating season. Lisbon and Eureka evolved in moist subtropics and the moisture also slows leaf drop from the cold-stress that brought the tree indoors in the first place. Dry indoor air is the single biggest cause of lemon spider mite explosions.

Mealybugs

Damage

High

Removal

Hard

What it looks like

Soft segmented bodies under a dusting of white wax, 2 to 4 mm long. Wedge into leaf-petiole joints, around the base of thorns on Lisbon, and at branch crotches near new growth. Slow movers and easy to miss because the cottony masses look like cobweb or fertilizer residue at a glance.

What the damage looks like

White fluffy patches in joints and along stems. Honeydew and sooty mold below. New leaves emerge twisted, undersized, or yellowed. A bad colony at bloom time will drop flowers before they set. Big lemon fruit takes 6 to 9 months to ripen, so losing a year of yield is a real cost.

How to get rid of them

Option 1

70% alcohol on a swab, every 3 days for 3 weeks

Dab every visible mealybug with a cotton swab dipped in 70% isopropyl alcohol. The wax shield melts and the bug dies on contact. Open up tight leaf-petiole junctions and crotches around the thorns to reach hidden colonies. Repeat every 3 days for 3 weeks. Eggs hatch in waves and only repeated passes break the cycle.

Option 2

Insecticidal soap and neem alternation for 4 weeks

Spray ready-to-use insecticidal soap on the underside of every leaf and into joint pockets at lights-out. The next week alternate to neem oil at the same coverage. Continue 4 weeks. Lemon mealybug eggs sit in tucked-away places that single-product runs miss.

Option 3

Move the tree away from other plants for the full treatment

Mealybugs spread by walking. Pull the tree at least 6 feet from other plants, citrus or otherwise. Wipe the windowsill, the saucer, and any tools that touched the infested tree before reusing. Treat any neighboring plant that was within reach as suspect.

Aphids

Damage

Medium

Removal

Easy

What it looks like

Small pear-shaped insects 1 to 3 mm long, in green, brown, yellow, or black depending on the species. Cluster densely on the soft tip growth of every spring flush and on the underside of just-unfurled leaves. Lemon trees push multiple flushes a year and aphids show up for nearly every one.

What the damage looks like

New shoots curl and twist, fragrant white blossoms drop early, and a sticky shiny film coats leaves below the affected tip. Sooty mold follows on the residue. Spring is peak season, when bloom and the first fruit set both happen, so aphid pressure during the flush hits yield directly.

How to get rid of them

Option 1

Hose blast on flush growth every 2 to 3 days for 2 weeks

Hold a hose nozzle 12 inches from each affected tip and hit it at high pressure. Most aphids dislodge and don't make it back. Cheapest, fastest fix and chemical-free. Repeat every 2 to 3 days for 2 weeks until new flush hardens off and aphids lose interest.

Option 2

Neem oil at dusk, every 5 days for 3 rounds

Mix 2 tablespoons cold-pressed neem oil and 1 teaspoon dish soap into 1 gallon of water.

Coat the underside of every young leaf and along the green tip growth at dusk. Avoid spraying open flowers if the tree is in bloom.

Repeat every 5 days for 3 rounds. The cycle covers egg through adult.

Option 3

Plant alyssum or yarrow within 3 feet of outdoor trees

For outdoor lemons in zones 9 to 11, tuck alyssum, dill, or yarrow within 3 feet of the trunk. The flowers feed ladybugs and lacewings, which eat aphid colonies down to nothing. A planted ring takes one season to establish and keeps spring flushes clean for years.

Distinctive squiggly silvery serpentine mines from leafminer larvae on a leaf

Leafminers

Damage

Low

Removal

Hard

What it looks like

The larva of a small silvery moth, around 4 mm long. The adult flies at night and is rarely spotted. The damage is what you see. The larva tunnels between the upper and lower surface of a young leaf. Outdoor pest in zones 9 to 11, mostly on the late-summer flush.

What the damage looks like

Snaking silver or whitish lines that wander across the surface of new leaves and widen as the larva grows. Affected leaves crinkle, fold, and stay disfigured for the life of the leaf. Mature leaves are not attacked and fruit is untouched. Visually alarming on a young Lisbon or Eureka but not a real threat to a healthy tree.

How to get rid of them

Option 1

Prune trail-marked shoots as soon as you see them

Snip off and bag every infested new shoot at the first sign of trails. The larva lives inside the leaf, so removing the affected growth removes the pest. Don't compost. Throw it in the trash. Outdoor lemons take this every late summer and the tree shrugs it off.

Option 2

Spinosad on new flushes, weekly through August to September

Use spinosad (Captain Jack's Deadbug Brew or Monterey Garden Insect Spray, ~$12 to $15). Spinosad penetrates the leaf surface enough to reach the miner.

Coat both sides of every flush leaf at dusk while the foliage is still soft and unfolded.

Repeat once a week through the late-summer moth peak in zones 9 to 11.

Option 3

Hold off heavy nitrogen feeding in late summer

Citrus leafminer attacks soft new growth, not hardened mature leaves. Skip nitrogen-heavy feeds from late July through September when adult moths are flying. Push the tree's main flush into early spring with a balanced citrus fertilizer instead. The spring leaves toughen up before moth season starts.

Stay ahead of all of them

Four habits that keep lemon tree pests rare and easy to catch.

Thorn-base and underleaf scan, every Sunday

Lisbon's thorns and the inner crotches of every lemon tree are exactly where scale and mealybugs hide. A 30-second weekly look at the underside of leaves and around the spine bases catches colonies before they move out across the canopy.

Quarantine any new citrus for 2 weeks

Nursery lemons often come home with scale crawlers or mealybug eggs in joint pockets. Two weeks isolated from your other citrus and houseplants gives a hidden infestation time to surface before it can jump to an established tree.

Wipe broad oval leaves with a damp cloth monthly

Lemon leaves are slick and large enough to wipe quickly. The pass clears dust, picks off early spider mites and scale crawlers, and lets you spot trouble while it's small. A clean canopy also photosynthesizes harder and supports better fruit set.

Move the tree indoors before nights drop below 50 degrees

Lisbon and Eureka are more cold-sensitive than Meyer and most owners winter them indoors. Bring the tree in before the first chilly night, set it near bright light, and start a humidifier the same day. Sudden moves into hot dry indoor air are what triggers winter spider mite outbreaks in the first place.

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About This Article

Kiersten Rankel M.S.

Botanical Data Lead at Greg · Plant Scientist

About the Author

Kiersten Rankel holds an M.S. in Ecology & Evolutionary Biology from Tulane University. A certified Louisiana Master Naturalist, she has over a decade of experience in science communication, with research spanning corals, cypress trees, marsh grasses, and more. At Greg, she curates species data and verifies care recommendations against botanical research.

See Kiersten Rankel's full background on LinkedIn.

Editorial Process

Pest identification and treatment guidance verified against Citrus x limon field reports from Greg's botanical database, cross-referenced with university extension sources and published horticultural research.

641+ Greg users growing this plant

USDA hardiness zones 9a–11b

Citations:
NC State Extension
Missouri Botanical Garden
Scale photo: Whitney Cranshaw, Bugwood.org (CC BY 3.0 US)
Spider mite photo: Clemson University - USDA Cooperative Extension, Bugwood.org (CC BY 3.0 US)
Mealybug photo: Gianni Del Bufalo (CC BY 2.0)
Aphid photo: Scot Nelson (CC0)
Citrus leafminer photo: Jeffrey W. Lotz, Florida Dept. of Agriculture, Bugwood.org (CC BY 3.0 US)
Leafminer photo: Jeffrey W. Lotz, Florida Dept. of Agriculture, Bugwood.org (CC BY 3.0 US)