Mandarin (Clementine) in Zone 9 -- plant

In a pot

Yes, on a dwarf rootstock, 15 gallons and up

Mandarins, especially a dwarf satsuma on Flying Dragon rootstock, are well suited to growing in a pot, because the trees are small to begin with. That also makes a pot the trick for cold climates: you can move it under cover when frost comes. Use a big pot with plenty of drainage holes and a loose citrus mix, and plan to water and feed more often than a tree in the ground.Mandarins are excellent container citrus: the trees are naturally small, and a satsuma on Flying Dragon (a dwarfing trifoliate rootstock) is well suited to a large pot. This makes the mandarin a strong cold-climate frost-escape play, a pot you can move under cover. Choose a large container with ample drainage holes, use a coarse citrus mix, and expect to water and feed more often than an in-ground tree.

Pot size: 15 gallons and up
Watering: Pots dry out much faster than the ground, especially in heat and wind, so check a potted mandarin often, maybe daily in summer. Water until it drips out the bottom, then let the top inch dry before watering again. Do not let the pot sit in a saucer full of water.Container trees dry out far faster than in-ground ones, especially in summer heat. Check the pot daily in hot or windy periods and water before the root zone dries out completely. Good drainage is critical: the saucer should stay empty, not pooling water against the roots. Frequent deep waterings plus a fast-draining mix keep a potted mandarin healthy. See the container watering note for detail.
Self-watering pot: Self-watering containers are risky for citrus and generally not recommended, because their constantly moist reservoir works against the soak-and-dry cycle citrus needs and raises foot-rot risk. If used at all, choose one with a true overflow and a coarse mix, let the reservoir empty between fills, and watch for overwatering signs.
Mix: Sharp drainage inside the pot is the priority. A mix sold for citrus or cactus works well, as does a quality potting mix lightened with extra perlite or coarse pine bark. Never use straight garden soil in a container because it packs tight and holds water against the roots. Blend in perlite, pumice, or coarse bark to sharpen drainage. The goal is a mix that drains freely after watering and never stays saturated, since a potted citrus is even less forgiving of wet feet than one in the ground.
Feeding: Feed more frequently than an in-ground tree at a lighter rate, using a micronutrient-inclusive citrus fertilizer, since pot leaching depletes nutrients and brings on chlorosis quickly. See the container fertilizer note for detail.

One to plant on

Flying Dragon trifoliate15 gal pot. Flying Dragon is a dwarfing rootstock that keeps the tree small, perfect for pots and small yards, and it is the key to growing mandarins in cold climates since you can move the pot under cover for winter. It also has the best cold hardiness of the common rootstocks and strongly resists root rot. The tradeoff is a smaller tree with a smaller crop, usually just what a container grower wants.15 gal pot. A naturally dwarfing mutation of Poncirus trifoliata producing very compact trees ideal for containers and small gardens, and the best cold hardiness of any widely available citrus rootstock. Excellent Phytophthora, nematode, and tristeza resistance. Sensitive to high-pH and saline soils. Fruit quality is good and trees are precocious, though total yield per tree is lower due to the small canopy, which suits a mandarin well.

Winter

If your winters are cold, growing a mandarin in a pot is the way to do it: keep it on a small (dwarf) tree and move the pot into a garage, sunroom, or by a bright window when frost is coming, then put it back outside when it warms. Mandarins, especially satsuma on a dwarfing rootstock, are well suited to this. While it is inside for winter, water it less and stop feeding it.For growers north of the in-ground range, a mandarin on Flying Dragon or another dwarfing trifoliate rootstock in a large pot is the standard cold-climate approach, and mandarins are especially well suited to it because the trees are naturally small. When frost threatens, move the tree into a garage, sunroom, or bright indoor spot, then back out once danger passes. Reduce water and hold fertilizer while it is held cool indoors.

Move the pot to a protected spot (garage, sunroom, or indoors by a bright window) before the first frost in cold-winter zones, and return it outdoors after frost danger passes. Hold the tree cool and bright, reduce watering, and stop feeding while overwintered. This portability is the whole advantage of growing a mandarin in a container outside its hardiness range.

Hardy to zone 8 in the ground; roots in a pot sit colder than that.

Pot safety

Ask what your balcony or roof can carry

A balcony or roof can only hold so much weight. Before you set heavy pots there, ask a building architect what it can safely carry.Illinois Extension's guidance is to consult a building architect about weight limits before placing heavy pots on a balcony or rooftop garden. It gives no weight figure.

Never grow food in a container with anything toxic in it

Many kinds of containers can be used. Whatever you choose, keep anything toxic out of it, especially if you are growing food.Colorado State accepts nearly any container material but warns against using a container that holds toxic materials, especially for edible plants. Illinois adds that a vegetable container should be free of chemicals toxic to plants or people, and urges caution with treated lumber when growing food. If you cannot account for what a repurposed container once held, that alone is a reason to keep food out of it.

Secure hanging containers well

Fasten hanging baskets and window or rail boxes securely. Think about what is below them too, since they can drip on people or things underneath.Illinois Extension asks growers to secure hanging containers well and to think through the safety issues of hanging them. Placement matters too, since a hanging container can drip onto people or belongings below.

Soil chemistry

Soil pH for mandarin (clementine)

Preferred

6 to 6.5

Tolerated

5.5 to 7.5

Mandarins like soil that is slightly acidic, around pH 6.0 to 6.5. The main thing to watch is alkaline (high pH) soil, common in the desert and inland West, where the tree cannot take up iron and zinc and the leaves yellow while the veins stay green. If that happens, use a citrus fertilizer that includes iron and zinc.Mandarins prefer a slightly acidic soil, roughly pH 6.0 to 6.5, and tolerate a somewhat wider band. The practical problem is high-pH alkaline soil (common in the desert Southwest and interior West), where iron and zinc become chemically unavailable and the tree shows interveinal chlorosis even though the nutrients are present. Correct with chelated micronutrients and a citrus fertilizer that supplies them.

Verified · 1 source View

Steady hand on the hose

Watering

When & how much

Frequency

Water deeply but not too often. Soak the root zone, then let the surface dry out, checking with a finger: when the top inch or two feels dry, water again. Water more often in hot weather and less in cool weather. Young trees dry out faster, but still let the surface dry between waterings and never keep the soil constantly wet.Deep and infrequent. Water established trees thoroughly, then let the top inch or two of soil dry before watering again; the interval stretches in cool weather and shortens in heat. Young trees need more frequent water to establish but still on a soak-and-dry pattern, never kept constantly wet.

Amount

Water enough to soak the soil deeply each time, out to the edge of the branches, not just a quick splash at the base. A few sprinkles do not reach the deep roots, so a long, thorough soak is better.Each irrigation should push moisture through the full root depth, which for a bearing tree means soaking the soil out to the canopy dripline. Frequent shallow sprinklings build weak surface roots that dry out fast; a mandarin's smaller root zone still wants a thorough soak, not a splash.

Method

Use drip emitters or a slow hose soak around the outer edge of the branches. Keep water off the trunk and the graft knob, because a wet trunk base can rot. Mulch under the tree, keeping the mulch away from the trunk, and keep grass out.Drip or low-volume emitters around the dripline, or a slow hose soak, are ideal. Keep water off the trunk and crown and never wet the graft union, since a constantly damp crown is a direct route to foot rot. Maintain a mulched, grass-free basin with mulch pulled back from the trunk.

Signs of trouble

Too much water

Signs of too much water are yellow, wilting leaves that do not perk up when you water, dropping leaves, soggy or bad-smelling soil, and gum oozing at the base of the trunk. The key clue is that watering makes the wilting worse, not better.Yellowing leaves that wilt but do not recover after watering, leaf drop, mushy or sour-smelling soil, and gumming at the trunk base are signs of overwatering and incipient foot rot. The tell is wilting that worsens, not improves, with more water.

Too little water

Leaves that curl or look dull and gray, wilting that perks back up after you water, dropping fruit, and dry, hard soil mean the tree is too dry. In hot weather a thirsty mandarin drops flowers and little fruit, so keep it evenly watered.Leaves that curl, cup, or dull and gray, wilting that recovers after watering, premature fruit drop, and a hard, dry root zone indicate underwatering. In heat, an underwatered mandarin drops flowers and small fruit, and the thin-skinned fruit can shrivel.

Feeding rhythm

Feeding

Frequency

split applications through the growing season

Type

citrus (nitrogen-forward, with iron, zinc, and manganese)

When to start

late winter or early spring through summer; stop by late summer

Mandarins are hungry for nitrogen and want most of their food during the growing season. Start feeding a grown tree as the weather warms in late winter or early spring, keep it up through summer in a few split doses, then stop by late summer so the new growth toughens before cool weather. A mandarin is a smaller tree than an orange, so it needs less total feed. Feed young trees smaller amounts more often. If your soil is alkaline, use a citrus fertilizer that includes iron and zinc so the leaves do not yellow, and do not overfeed, since soft growth draws pests.Mandarins are nitrogen-hungry like all citrus and feed best on a rhythm concentrated in the growing season. Feed a bearing tree from late winter or early spring through summer in split applications, and stop by late summer so the fall flush hardens before winter cold. Because mandarins are smaller trees than a navel orange, scale the total nitrogen down accordingly. Young trees get smaller, more frequent doses to build the framework. On alkaline soils use a citrus fertilizer that supplies iron, zinc, and manganese as chelates and water it in. Over-fertilizing pushes soft flush that draws aphids, leafminer, and psyllid.

N · P · K = 2-1-1

A fertilizer made for citrus (look for one labeled citrus); these are higher in nitrogen and include the iron and zinc citrus needsA nitrogen-forward citrus formulation (for example a 2-1-1 ratio) with included micronutrients (iron, zinc, manganese), or a product labeled specifically for citrus

Who grows well together

Companion planting

Keep grass and lawn out from under a mandarin tree, since grass steals the water and food the tree's shallow roots need. A ring of mulch, kept back from the trunk, beats grass growing right up to the tree. There is little real benefit to planting things close around citrus. Keep turf and lawn grasses out of the root zone. Grass competes hard for water and nutrients in the shallow layer where citrus feeder roots concentrate, and mowers damage the trunk. A mulched, grass-free basin out to the canopy dripline is the standard recommendation for all citrus, mandarins included. Low, shallow-rooted covers or a cool-season legume kept outside the trunk flare add living mulch without root competition. Mandarins fruit on a single tree, so no pollinizer companion is required; in fact nearby pollen-bearing citrus can put seeds into otherwise seedless fruit.

Other

Yarrow

Yarrow is a low, tough plant with flat flower heads that pull in ladybugs, lacewings, and other good bugs that eat aphids. It is shallow-rooted and easygoing, so it does not crowd the tree as long as you keep it out toward the edge of the canopy. Let it flower to get the benefit.A low, shallow-rooted plant that draws beneficial insects and does not compete with citrus roots when kept outside the dripline. Traditional

Fava bean

A cool-season nitrogen fixer grown beyond the dripline as a winter cover, then cut and dropped to feed the soil without crowding the tree. Research-backed

White clover

A low clover outside the trunk area works as a living mulch and adds a little nitrogen, without stealing water the way lawn grass does. Research-backed

Marigold

A simple flower that brings in helpful insects and fills bare ground around the tree. Plant it beyond the trunk, not tight against it. Traditional

Keep apart from

St. Augustine grass St. Augustine is a thick, fast-spreading lawn grass that is rough on citrus. It soaks up water and food in the top layer of soil where the tree's roots feed, and it creeps to the trunk. Keep a clear or mulched circle around the base and hold the grass back beyond it.A dense, spreading lawn grass that competes aggressively for water and nutrients in the topsoil and creeps right up to the trunk. Keep it cleared out to the dripline. Research-backed

Turf grass Lawn grass under the tree steals the water and food the mandarin's shallow roots need. A ring of mulch, kept back from the trunk, is better than grass. Research-backed

Bermuda grass A tough, spreading lawn grass that competes hard for water and is difficult to keep out of the root zone. Clear it out to the edge of the branches. Research-backed

Provenance tagged inline · see methodology for the labeling system Key

Harvest signals

When to pick

Pick mandarins by taste, not just by color, and do not leave them on the tree too long. The skin loosens and colors as fall nights get cool, but in warm, humid areas it can still look a little green even when the fruit is ripe, so taste one first. Unlike oranges, most mandarins get puffy and dry inside if left on the tree, so pick them when ripe and keep them in the fridge. A few late types like Gold Nugget and Pixie are the exception and do hold on the tree into spring. Early satsumas also let you pick the crop before the coldest weather.Harvest mandarins by taste, and pick promptly. The rind loosens and puffs slightly and color deepens as cool fall nights arrive, but in warm, humid climates the rind can stay green-tinged on fully ripe fruit, so taste rather than color decides. Unlike a navel, most mandarins do not hold well on the tree: satsuma and early types puff, dry, and lose flavor if left past maturity, so pick at ripeness and refrigerate. The exceptions are the late holding types, notably Gold Nugget and Pixie, which keep their quality on the tree into spring. Early satsuma ripening also lets the crop come off before the hardest winter cold.

Yield

What to expect

A grown mandarin makes a good crop, though less than a big orange tree because the tree is smaller, often tens of pounds up to around a hundred pounds a year in good conditions. It depends on the variety, climate, and tree size. A small dwarf tree in a pot makes much less, but still enough to enjoy.A mature standard mandarin yields less than a full-size navel because the tree is smaller, commonly on the order of tens of pounds up to roughly a hundred or more pounds per year under good conditions, varying widely with variety, climate, tree size, and rootstock. Dwarf container trees yield far less but still give a worthwhile home crop.

A mandarin hits its full crop around four to seven years old and then produces for decades. Mandarins tend to bear a big crop one year and a light one the next, which is normal; thinning the heavy year evens it out.Trees reach full production around the fourth to seventh year and then bear for decades. Mandarins are strongly alternate-bearing, so expect a marked swing between heavy and light crop years unless heavy years are thinned; this is normal for the group and managed rather than cured. Young trees need their first-year energy in roots and branches, not fruit, even though a mandarin may want to fruit early. Snap off any first-season flowers. Fruit will start coming around year two or three, with a real crop as the tree grows. Building up first gets you more fruit in the long run.Strip any flowers that set in the first season so the tree puts its energy into roots and framework rather than fruit, even though mandarins are precocious and may try to bear early. Light bearing typically begins in year two or three, with a full crop building as the tree matures. The early investment pays back in stronger, earlier-peaking production.

Verified · 2 sources View

Off the vine

Storing your harvest

Room temp

Once picked, mandarins last about a week on the counter, a bit less than an orange because the skin is so thin. They are best eaten fresh and soon.Picked mandarins keep about one week at room temperature, less than a thick-skinned orange because the loose, thin rind offers little protection. Use them fresh; the whole appeal of a mandarin is eating it soon after picking.

Fridge

In the fridge, mandarins last two to four weeks. Keep them loose or in a bag with holes so they do not get damp and moldy. Unlike oranges, mandarins do not keep well left on the tree, so the fridge is the way to store them.Refrigerated at about 32 to 36°F, mandarins hold two to four weeks. Store them loose or in a perforated bag so they do not sweat, and do not seal them airtight. Unlike a navel, a mandarin does not store well by leaving it on the tree, so the refrigerator, not the branch, is the place to hold the crop.

Freezer

Whole mandarins do not freeze well, but the juice does. Squeeze the juice and freeze it in a sealed container for up to about six months. You can also freeze the zest for cooking.Whole mandarins do not freeze well, but the juice freezes excellently. Squeeze and freeze juice in airtight containers for up to about six months, and segments can be frozen in light syrup. Zest freezes for baking.

Verified · 2 sources View

When something goes wrong

Common problems

The mandarins are green and sour even though the tree seems fineFruit stays green and tart even though the tree looks healthy

01 of 05

What happened Mandarins need cool fall nights and enough warmth to turn sweet and colored. In very warm, humid places (like low-elevation tropics) or the coolest foggy coast, the tree makes fruit but it can stay green and sour because the weather does not have the warm-day, cool-night swing that sweetens it. It is a climate thing, not something you did wrong.Mandarins color and sweeten with cool fall nights and adequate warmth in the season. In the warm, humid tropics and on the coolest coastal strips the tree grows and sets fruit but the fruit can stay green-skinned and low in sugar because the climate lacks the diurnal swing (warm days, cool nights) that develops mandarin quality. This is less demanding than a navel's high-heat requirement, but it is still a climate limit, not a care mistake. Next season You cannot fix the climate with watering or feeding. Pick varieties suited to your area (satsuma handles cooler summers well) and a warm, sheltered spot helps a little. In the tropics, cooler hillsides make better fruit.There is no cultural fix for the missing climate signal. In a marginal-quality area, choose the varieties best suited to it (satsuma tolerates cooler summers; some mandarins fruit at low heat) and a warmer microclimate can help at the margin. In the tropics, cooler uplands give better fruit.

The fruit looks ripe but is puffy and dry insideFruit is puffy, dry, or loose inside despite looking ripe

02 of 05

What happened Most mandarins, unlike oranges, do not keep well on the tree. Satsumas and early types get puffy (the skin balloons away from the fruit) and dry inside if left on too long. The skin can still look fine even when the inside has gone dry. The fix is to pick them when ripe and store them in the fridge.Unlike a navel orange, most mandarins do not hold well on the tree. Satsuma and other early types puff (the rind separating and ballooning away from the flesh) and dry out if left on the branch past maturity, losing juice and flavor. The rind can look fine while the interior declines. This is the mandarin storage reality: pick promptly and refrigerate rather than storing on the tree. Next season Pick most mandarins as soon as they are ripe and keep them in the fridge instead of on the tree. If you want fruit that can wait on the tree into spring, plant a late type like Gold Nugget or Pixie.Pick early and mid-season mandarins promptly at maturity and refrigerate them rather than leaving the crop on the tree. If you want fruit that keeps on the branch into spring, grow a late holding type such as Gold Nugget or Pixie, which are the exception.

A big crop one year and hardly any the nextA huge crop one year, then almost none the next

03 of 05

What happened Mandarins tend to make a big crop one year and then very little the next. A heavy crop tires the tree and cuts down the growth that would carry next year's flowers, so it swings back and forth. This is normal for mandarins, not a sickness.Alternate bearing (a heavy on-year followed by a light or bare off-year) is a strong, well-known tendency in mandarins, far more pronounced than in sweet oranges. A very heavy crop suppresses the next year's flowering by consuming the tree's carbohydrate and inhibiting the shoot growth that carries next spring's bloom, so the tree swings between extremes. It is normal for the group, not a disease. Next season In a big-crop year, pick off some of the fruit in early summer so the tree is not overloaded, which helps it flower and fruit again the next year. Steady feeding and watering help too.Thin heavy on-year crops in early summer, the earlier the better, to even out the cycle; hand thinning or light pruning of a loaded tree reduces the drain and improves next year's bloom. Steady feeding and watering also soften the swing.

Leaves turning yellow but the veins stay greenYellowing leaves with green veins (iron or zinc chlorosis)

04 of 05

What happened When leaves turn yellow but the veins stay green, especially on new growth, the tree is short on a micronutrient, usually iron or zinc. This happens a lot on alkaline (high pH) soils in the desert and inland West, where the nutrient is in the soil but the tree cannot take it up. It looks different from an even all-over yellowing (usually nitrogen) and from the blotchy yellowing of greening.Yellow leaves with a network of green veins, especially on new growth, signal a micronutrient deficiency, most often iron or zinc, common on alkaline, high-pH soils where the nutrients are present but chemically unavailable. This is widespread in desert and interior-West soils. It is distinct from the symmetric overall yellowing of nitrogen shortage and from the blotchy asymmetric yellowing of greening disease. Next season Fix it with a chelated iron or zinc product, sprayed on the leaves for a fast response and added to the soil for the long run, and use a citrus fertilizer that lists micronutrients.Correct with a chelated iron or zinc product, applied as a foliar spray for a quick response and to the soil for longer-term supply, and use a citrus fertilizer that includes micronutrients.

The tree is dropping a lot of leaves or fruitSudden leaf drop or heavy fruit drop

05 of 05

What happened A few things cause drop. Cold: after a freeze a mandarin (which never goes dormant) can wilt and drop leaves days later, and the fruit can be hurt near 30°F even though the wood is hardier. Too much water or poor drainage rots the roots and drops leaves, and the clue is that watering makes it worse. A hot spell during bloom also drops flowers and little fruit.Several causes look different but end in drop. Cold injury follows a freeze, with leaves wilting, browning, and dropping days later on an evergreen tree that never goes dormant, and fruit can be damaged near 30°F even though the wood is hardier. Overwatering and poor drainage are the other frequent culprit: saturated roots and incipient foot rot cause yellowing and drop, with the tell being leaves that wilt but do not recover after watering. A spring heat spike during or just after bloom also drops flowers and young fruit. Next season Figure out the cause. If it was frost, protect the tree better next time and wait until spring to trim damaged wood. If it is overwatering, water less, make sure the soil drains fast, and check the graft knob is not buried. If a heat wave hit during bloom, keep the tree well watered through hot spells.Distinguish the cause first. For cold, improve frost protection and wait until spring growth to see what survived before pruning. For overwatering, back off irrigation, confirm sharp drainage, and check the graft union and crown are not buried. For heat-spike drop, keep moisture even and bump irrigation through the hot spell during bloom.

Verified · 8 sources View

The usual suspects

Pests & diseases

Pests

Asian citrus psyllid

P · 01

Symptoms This tiny brown insect rests on new leaves at an angle, rear end raised, which is your clue. The young ones make little waxy white threads and curl the new leaf tips. The real danger is not the feeding but a fatal disease it spreads, citrus greening, so it is worth acting on even where the pest is uncommon.A tiny mottled-brown insect, about an eighth of an inch, that feeds tilted up at a 45-degree angle on new flush, a posture no other citrus pest shares. Nymphs make waxy tubules and curl tender growth. The insect matters less for its feeding than for what it carries: it is the vector of Huanglongbing (citrus greening), the most serious citrus disease worldwide. Scout the youngest flush. Cause The psyllid breeds on fresh new leaves, so it builds up fastest when the tree is pushing tender growth in warm weather. It has spread across the southern states, and any psyllid you find could be carrying the disease.Adults lay eggs only on new flush, so populations track flushing cycles and build fastest in warm weather when the tree pushes tender growth. The pest is established across much of the southern United States, and any psyllid should be treated as a potential disease carrier. Organic treatment Spray horticultural oil or insecticidal soap on the new growth to knock back the young psyllids, repeating each time fresh leaves appear. Hold off on oil when it is above about 95°F or the tree is short on water, or the oil can burn leaves. Also report any psyllids or signs of the disease to your local farm advisor.On a backyard tree, horticultural oil and insecticidal soap on the new flush reduce nymphs; thorough coverage is key, repeated as each flush emerges. Do not apply oil above 95°F or to a drought-stressed tree. Most important, report suspected psyllids or greening symptoms to your county agricultural office, since this is a regulated pest. Prevention Buy certified citrus from a trusted nursery, and never carry citrus plants or cuttings out of a quarantine zone, since that is how the pest and its disease spread. Check new leaves often in warm weather, and follow local guidance if greening is in your area.Buy only certified citrus from a reputable nursery and never move citrus plants or leaves out of a quarantine area, the main way the pest and disease jump regions. Inspect each flush in the warm season, and conserve the parasitic wasp Tamarixia and general predators that suppress it.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Beneficial predators

Leave the tiny parasitic wasp Tamarixia and the general predators already in your yard to work on the psyllid, and keep strong broad-spectrum insecticides off the tree, since those take out the helpers along with the pest.Tamarixia and resident generalist predators suppress psyllid numbers, so conserving them is a working control rather than a courtesy. Broad-spectrum material removes them along with the target, and the population they were holding down rebuilds on the next flush.
Insecticidal soap

On a backyard tree, insecticidal soap sprayed onto the new leaves knocks back the young psyllids, which is the stage it reaches. It works only where it lands, so cover the fresh growth thoroughly and spray again each time another round of leaves pushes out.Soap reduces nymphs on the flush and acts only on contact, so coverage of the expanding growth decides the result and applications follow flushing rather than a calendar. It does not stand in for the reporting and quarantine steps above it, which are what act on the disease risk.
Horticultural oil

Horticultural oil, a light spray oil that smothers insects rather than poisoning them, does the same job on the new growth. Hold off in hot weather and when the tree is short of water, or the oil can burn the leaves, and repeat with each new flush, since it wears off quickly.Oil on emerging flush reduces nymphs by contact, so thorough wetting of the tender growth governs the outcome and timing tracks the flushing cycle. Withhold it in hot weather or on a drought-stressed tree, where foliage injury follows.

No spray for this one. Prevention is the control.

Citrus leafminer

P · 02

Symptoms You will see squiggly silver trails snaking through the new leaves, often with the leaf edge curled. A tiny caterpillar makes these tunnels inside young leaves only. It looks alarming but rarely hurts a grown tree, though it can set back a small young one.Silvery, serpentine tunnels winding through new leaves, with a thin dark frass line down each mine and leaf margins that curl around the damage. The larva mines only young, expanding foliage; hardened leaves are not attacked. On an established tree the injury is cosmetic, but on a young mandarin pushing lots of flush it can slow growth. Cause A tiny moth lays eggs on the newest leaves, and the larvae tunnel inside them. They breed fast in warm weather, so the worst damage shows on the late-summer growth.A small moth lays eggs on tender new flush, and the larvae mine between the leaf surfaces. Generations cycle quickly in warm weather, so damage peaks on the late-summer and fall flushes rather than spring growth. Organic treatment Usually no treatment is needed, and spraying can kill the good bugs that control it. On a small young tree you want to protect, light horticultural oil on the new leaves discourages the moth. Only spray in mild conditions, not in high heat or on a thirsty tree, and leave the tunneled leaves on.Chemical control is rarely warranted, and broad-spectrum sprays undermine the parasitic wasps. On a young tree where mining slows establishment, a light horticultural oil at bud break discourages egg-laying on the new flush; repeat as each flush emerges. Follow label heat limits and do not spray above 95°F. Leave mined leaves in place. Prevention Do not over-fertilize or prune a lot in summer, because that creates the tender leaves the moth needs. On a healthy grown tree it is best to live with the trails, since helpful wasps keep it in check.Avoid forcing excess tender flush with heavy nitrogen or unnecessary summer pruning, since the moth needs young leaves to breed. Tolerate cosmetic mining on bearing trees; resident parasitic wasps usually provide good control when broad-spectrum sprays are avoided.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Balance nitrogen

Go easy on nitrogen fertilizer and skip unnecessary summer pruning. Both push out extra soft new leaves, and soft new leaves are the only tissue the young leafminer can tunnel into, so fewer of them out of season means fewer targets.Flush management is the whole cultural lever, since the larva mines only young, expanding foliage and hardened leaves are not attacked. Restrained nitrogen and no unnecessary summer cuts keep growth waves synchronized and shorten the window of susceptible tissue, which matters most on the late-summer and fall flushes when generations cycle fastest.
Beneficial predators

On a grown tree the trails look worse than they are, and the small parasitic wasps living in the canopy usually keep the leafminer in check on their own. What keeps that working is leaving broad-spectrum sprays out of the tree, since they kill the wasps too.Resident parasitic wasps usually provide good control where broad-spectrum sprays are avoided, which is the argument for tolerating cosmetic mining on a bearing tree. Chemical control is rarely warranted, and a spray that undermines the parasitoids costs the tree more than the mining does.
Horticultural oil

On a small young tree where mining is slowing growth, a light horticultural oil, a thin spray oil, on the leaves as they open discourages the moth from laying there. It wears off quickly, so recoat each fresh round of leaves, spray only when conditions are mild rather than during a hot spell or when the tree is short of water, and leave the tunneled leaves where they are.Reserve oil for a young tree where mining slows establishment, applied to the flush at bud break and renewed as each flush emerges, since the residual is brief. Follow the label heat limits and withhold it on a drought-stressed tree. Leave mined foliage in place rather than stripping it.

No spray for this one. Prevention is the control.

Scale insects

P · 03

Symptoms Scale look like little hard or waxy lumps that sit still on twigs and leaf undersides, so it is easy to mistake them for part of the branch. The soft kinds make leaves sticky and grow a black sooty coating, and ants are often crawling around them.Fixed, non-moving bumps clustered on twigs, along the leaf midrib, and beneath leaves. Armored types form firm gray or brown shells like raised bark; softer types are plumper and glossy and secrete honeydew that leaves foliage tacky and grows black sooty mold, with ants patrolling for the sugar. Heavy numbers bring mottled yellow leaves, early leaf fall, and twig dieback. Cause Scale are little insects that feed on the tree's sap. They get worst when ants are around, since the ants protect them from the helpful bugs that eat scale.A mix of armored and soft scale species tap into the tree and feed on sap. They gain the upper hand on trees that are dusty, crowded, or patrolled by ants, since ants drive off the ladybugs and parasitic wasps that would thin the colony. Organic treatment Coat the lumps with horticultural oil, reaching the backs of leaves and the twigs. Save the spray for cooler, well-watered days, never above roughly 95°F or on a stressed tree, or it can scorch the foliage. Spray again later as new ones appear.A thorough horticultural oil application, narrow-range petroleum or neem, smothers scale; the key is wetting every surface, especially twig undersides and leaf backs. Skip oil above roughly 95°F or on a drought-stressed tree. Plan a follow-up as fresh crawlers hatch. Prevention Keep ants from climbing the tree with a sticky band around the trunk, which lets the good bugs control the scale, and look over any new tree for lumps before planting it.Keep the tree vigorous, rinse dust off the canopy, and cut off ants with a sticky trunk band so resident beneficials can work. Inspect any incoming nursery tree, since scale often hitchhikes on new stock.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Ant exclusion

Look for ants running up the trunk. While they are patrolling the tree they chase off the ladybugs and parasitic wasps that would otherwise work the colony down, so shutting the ants out is what changes the situation. Wrap the trunk with heavy paper, duct tape, or fabric tree wrap and put the sticky material on that wrap rather than on bare bark, which it can injure. Then trim back any low branch touching the ground, a wall, or a neighboring plant, since ants walk around a band by those routes.Ant tending is what holds scale above the level resident predators and parasitoids would allow, so cutting ant access to the canopy comes before anything aimed at the insects themselves. Per UC IPM, band over a collar of heavy paper, duct tape, or fabric tree wrap instead of bare bark, and close the bypass routes in the same pass by skirt pruning the branches that bridge to soil, a wall, or an adjacent plant.
Beneficial predators

With the ants shut out, the ladybugs and small parasitic wasps already in the tree do much of the work on scale for free. Keep strong broad insecticides off the tree so they stay in it.Predators and parasitic wasps thin scale colonies wherever ants are not driving them off, which is what makes the exclusion work pay. Broad-spectrum material removes them, and the colony rebuilds on the same twigs and leaf undersides.
Horticultural oil

For a heavy case, coat the bumps with horticultural oil, a light spray oil that smothers them rather than poisoning them; a narrow-range petroleum oil or a neem oil both do this. Coverage is the whole job, so wet the undersides of the twigs and the backs of the leaves, because a bump the spray misses survives. Save it for cooler, well-watered days rather than a hot spell or a tree already short of water, since the spray can scorch leaves under either condition, and go back over the tree later as the young crawling stages hatch.A thorough narrow-range petroleum or neem oil application smothers settled scale, so wetting the twig undersides and the backs of the leaves, where colonies are otherwise missed, governs the result more than rate does. Skip it in hot weather or on a drought-stressed tree, and plan a follow-up timed to fresh crawler emergence rather than treating once.

No spray for this one. Prevention is the control.

Aphids

P · 04

Symptoms Look for clusters of tiny soft-bodied insects, often green or black, packed onto the newest leaves and flower buds, curling the tips. They leave a sticky coating that ants follow and that grows a black sooty film. Mandarins are most vulnerable during the spring and fall flushes.Clusters of soft green, black, or brown aphids on the youngest flush and flower buds, with curled, distorted new leaves and sticky honeydew that draws ants and grows sooty mold. Spring and fall flushes are the targets. The brown citrus aphid is also a vector of citrus tristeza virus, which raises the stakes where that disease is a concern. Cause Aphids multiply very fast on soft new growth in mild weather, and ants protect them. Too much fertilizer makes extra tender leaves that draw them in.Aphids reproduce explosively on tender new growth in mild weather and are tended by ants for honeydew. Lush, over-fertilized flush is especially attractive, and ant protection lets colonies outrun their natural enemies. Organic treatment Spray them off with water, or use insecticidal soap or horticultural oil, getting under the curled leaves. Keep oil for mild days only, not in high heat or on a stressed tree, and avoid harsh sprays that kill the good bugs.A forceful water spray, insecticidal soap, or horticultural oil controls aphids; cover the undersides of curled leaves and repeat as needed. Observe oil heat limits (not above 95°F or on stressed trees), and preserve natural enemies by skipping broad-spectrum insecticides. Prevention Do not over-fertilize, which makes the soft growth aphids love, and keep ants out so ladybugs and other helpers can eat them. A blast of water from the hose usually clears them off.Avoid forcing excess tender flush with heavy nitrogen. Control ants so ladybugs, lacewings, and parasitic wasps can suppress colonies. A strong jet of water knocks aphids off new growth and is often all that is needed.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Balance nitrogen

Ease off the fertilizer. Heavy feeding pushes out wave after wave of soft new leaves, and that tender growth is exactly what aphid colonies pile onto.Lush, over-fertilized flush is what these colonies build on, so restrained nitrogen narrows the supply of susceptible tissue rather than acting on the insects. Pressure concentrates on the spring and fall flushes, which is when the feeding habit pays.
Water spray

Knock the clusters off the new growth with a strong jet from the hose. On a backyard tree that is often the whole job, and it leaves the helpful insects working the same leaves alone.A forceful jet dislodges colonies from tender shoots without setting back the natural enemies on the same flush. Aim it into the curled shoot tips and repeat rather than escalating while numbers are still low, and time it so the foliage dries.
Ant exclusion

Check the trunk for a line of ants following the honeydew, the sticky waste the aphids leave behind. Where ants are present they defend the aphids from the ladybugs, lacewings, and parasitic wasps, so shutting them out lets those helpers finish the job. Collar the trunk with heavy paper, duct tape, or fabric tree wrap and put the sticky material on the collar rather than on bare bark. If no ants are working the tree, this one does not apply.Ant protection is what lets colonies outrun their natural enemies, so exclusion shortens an outbreak rather than treating it. Apply the sticky material over a paper, tape, or fabric collar instead of bark, and close the branch bridges to soil, a wall, or a neighboring plant that let ants route past the trunk. Where no trail is present, this is not the situation it addresses.
Beneficial predators

Low numbers are worth tolerating. Ladybugs, lacewings, and small parasitic wasps suppress aphid colonies on their own, and a broad spray sets those helpers back harder than it sets back the aphids.Lady beetles, lacewings, and parasitoids suppress colonies once ants are not shielding them, which is the reason to keep broad-spectrum insecticides out of the canopy. Conservation is the operative control on an established tree.
Insecticidal soap

If a young tree is heavily covered, insecticidal soap sprayed straight onto the clusters brings the numbers down. It kills only what it wets, so get in under the curled leaves where the colonies sit.Soap is contact-only and worth reaching for where colonies are heavy on a young tree, directed into curled leaves and shoot tips so it reaches the insects rather than the beneficials it would otherwise wet. Repeat as needed instead of on a fixed schedule.
Horticultural oil

Horticultural oil, a light spray oil, is the other option and works the same way, by coating rather than poisoning. Cover the undersides of the curled leaves, and keep it for mild days rather than hot weather or a tree that is short of water, since it can burn foliage then.Oil is interchangeable with soap here, with the same coverage requirement into curled foliage and the same limits in hot weather and on a drought-stressed tree. Neither material changes the case for keeping broad-spectrum insecticides off the tree, which is the natural enemies working the same flush.

No spray for this one. Prevention is the control.

Citrus red mite

P · 05

Symptoms Look for leaves that turn a dull, speckled, silvery color, sometimes with tiny red dots moving on them (a hand lens helps). Mites get worse when it is hot, dry, and dusty. A lot of them can bronze the leaves and drop some.Fine stippling or silvering on leaves and sometimes the rind, with tiny dark-red mites and cast skins visible under a hand lens. Heavy populations bronze the foliage and can drop leaves. Mites flare in hot, dusty, dry conditions and after broad-spectrum sprays remove their predators, so an outbreak often signals a dust-stressed or over-sprayed tree. Cause These mites love hot, dusty conditions and build up fast on stressed trees. Dusty trees and trees sprayed with strong insecticides (which kill the helpful mites) get the worst of it.Citrus red mite thrives in heat and dust and reproduces rapidly on stressed trees. Dusty roadside trees and trees sprayed with broad-spectrum insecticides, which remove predatory mites, are the most prone to damaging populations. Organic treatment Usually the damage is just cosmetic and needs nothing. If there are a lot of mites, horticultural oil works, but timing is tricky: mites peak in hot weather, the riskiest time to oil a tree. Only spray once it has cooled off, never on a hot, dry, stressed tree.Damage is usually cosmetic and rarely needs treatment. If populations run heavy on a stressed tree, horticultural oil provides control; observe heat limits strictly, as mite outbreaks coincide with the hot weather when oil is riskiest. Do not apply oil above 95°F or to a drought-stressed tree. Prevention Rinse dust off the leaves during hot, dry weather and keep the tree watered, because a healthy tree handles mites better. Avoid strong insecticides that kill the good mites.Hose dust off the canopy in hot, dry spells and keep the tree well watered, since vigorous trees tolerate mites better. Avoid broad-spectrum insecticides that destroy the predatory mites providing natural control.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Even watering

Keep the tree watered steadily instead of letting it swing between soaked and bone dry. These mites build up fastest on a stressed tree, and a well-watered one puts up with them better.Citrus red mite reproduces rapidly on stressed trees, so steady soil moisture is the baseline rather than an afterthought. A vigorous tree tolerates the feeding, which is why the water regime does more here than any spray timing.
Water spray

Hose the dust off the leaves during hot, dry spells. Dust is part of what lets these mites build up, and rinsing the canopy brings numbers down without harming the good mites that eat them.Rinsing the canopy strips the dust layer that favors buildup and suppresses the population directly, which is why dusty roadside trees carry the heaviest infestations. Repeat it through a dry spell rather than escalating on the first stippling, since the physical knock-back leaves predatory mites intact.
Beneficial predators

Predatory mites eat the pest mites for free. Broad-spectrum insecticides kill those predators, and mite trouble often gets worse after that kind of spray, so leave the strong products out of the tree.Predatory mites provide the natural control, and broad-spectrum insecticides remove them, which is why an over-sprayed tree is among the most prone to damaging populations. A flare-up is often a reading of the spray history rather than of the season.
Horticultural oil

The speckling is usually just cosmetic and needs nothing at all. If a stressed tree is carrying a lot of mites, horticultural oil, a light spray oil, works on contact, but the timing is awkward: mites peak in hot weather, which is the riskiest time to oil a tree. Wait until it has cooled off, water the tree first, and cover the leaves where the mites are sitting.Damage is usually cosmetic and rarely warrants treatment. Where populations run heavy on a stressed tree, oil gives control by contact, so coverage decides the result; observe the heat limits strictly, since populations peak in the same hot weather that makes an oil application riskiest, and withhold it on a drought-stressed tree.

No spray for this one. Prevention is the control.

Diseases

Huanglongbing (citrus greening, HLB)

D · 01

Symptoms The classic sign is a leaf yellow in a blotchy, uneven pattern, with the yellow on one side not matching the other (a nutrient problem is usually even on both sides). Fruit stay small, lopsided, green on the bottom, and taste bad. There is no cure, and the tree slowly dies. It is the worst citrus disease there is.Blotchy, asymmetric leaf yellowing that does not mirror across the midrib (distinguishing it from a symmetric nutrient deficiency), yellow shoots, and corky, enlarged veins. Fruit are small, lopsided, fail to color fully, stay green at the bottom, and taste bitter and salty; seeds often abort. The tree declines over years and there is no cure. This is the most destructive citrus disease worldwide. Cause Bacteria spread by the Asian citrus psyllid as it feeds on new shoots clog the tree's plumbing, blocking food to roots and fruit. No treatment reverses it; an affected tree is a permanent source of spread. Management is preventing psyllid feeding and removing any confirmed tree.Candidatus Liberibacter asiaticus, the bacterium behind greening, spreads tree to tree by the Asian citrus psyllid feeding on new growth, then clogs the phloem so nutrients cannot reach roots and fruit. No treatment clears an established infection, so management is entirely suppressing the psyllid and removing confirmed trees before they seed further spread. Organic treatment There is no treatment that saves an infected tree. Focus entirely on prevention: keep the psyllid off with regular inspection and treatment, and if a tree is diagnosed with greening, remove it promptly to protect nearby trees. An infected tree left in place becomes an ongoing source of psyllid pressure.There is no cure and no organic remedy for an infected tree. Management is prevention and vector control only: protect trees from the psyllid, and remove and properly dispose of confirmed-infected trees promptly so they cannot serve as a reservoir. Prevention Buy only certified clean trees, never move citrus out of a quarantine zone, and control the psyllid that spreads it. Check your tree often, and report anything that looks like greening to your local agricultural office, because removing infected trees quickly protects everyone's citrus.Plant only certified disease-free nursery trees, never move citrus out of quarantine areas, and control the psyllid aggressively where it is present. Inspect regularly and report suspected greening to your county agricultural commissioner, since coordinated removal of infected trees is the only effective area-wide defense.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Certified clean stock

Buy only certified disease-free citrus from a reputable nursery, and do not bring a citrus plant or cuttings in from an area under quarantine, a legal restriction on moving citrus. Starting with a clean tree is the part of this fully in your hands, because nothing clears the bacterium once it is inside a tree.Certified disease-free nursery stock is the controllable half of the response, since an established infection is not cleared by any treatment. Observe the quarantine restrictions on moving citrus plant material, which is the route by which both the pathogen and its vector jump regions.
Garden sanitation

Look the tree over regularly for blotchy, uneven yellowing that does not match from one side of the leaf to the other, and report a tree you suspect of greening to your county agricultural office. If a tree is confirmed infected, take it out promptly and dispose of it the way local rules direct, since it cannot be saved and while it stands it keeps supplying the psyllid that carries the disease to trees nearby.Removing a confirmed infected tree is inoculum management rather than treatment: while it stands it remains a reservoir the vector acquires the bacterium from. Report suspected cases to the county agricultural commissioner, since coordinated removal is the effective area-wide defense, and keep the psyllid off healthy trees, since suppressing the vector and taking out confirmed trees are what the management program consists of.

No spray for this one. Prevention is the control.

Phytophthora foot rot, root rot, and gummosis

D · 02

Symptoms Look for gum oozing near the base of the trunk and a dark, sunken, slimy patch under the bark, along with a thinning, yellowing canopy. A key clue is leaves that wilt and do not perk up when you water, because the roots are rotting from too much water.A trunk lesion at or near the bud union, appearing first as a drop of gum, then a brown, necrotic, slippery area under the bark that can girdle the trunk. Below ground, dark, rotted feeder roots go with a thinning, yellowing canopy and leaves that wilt but do not recover after watering. It is one of the most serious threats to a citrus tree, and it follows wet feet and a buried graft union. Cause A soil fungus attacks the roots and trunk base when the soil stays too wet. Poor drainage, overwatering, and burying the graft knob are what let it in.Soil-borne Phytophthora species attack roots and the crown wherever soil stays saturated. A buried or mulch-packed graft union, poor drainage, and overwatering are the drivers; heavy clay and standing water are the classic setups. Organic treatment There is no easy fix once it takes hold. Improve the drainage, clear soil and mulch away from the trunk base so it can dry out, and water less. The best control is preventing it with good drainage and planting the tree high in the first place.There is no quick cure once the crown is girdled. Correct the cause: improve drainage, pull soil and mulch back from the crown to let it dry, and cut back irrigation. Minor bark lesions can sometimes be exposed and allowed to callus. Prevention through drainage and planting depth is the real control. Prevention Plant on a raised mound with the graft knob above the soil, make sure water drains fast, keep mulch off the trunk, and let the soil dry between waterings. Buying a tree on a root-rot-resistant rootstock also helps a lot.Plant high on a mound with the graft union well clear of the soil, guarantee sharp drainage, keep mulch off the trunk, and water with a soak-and-dry rhythm rather than constant moisture. Choose a Phytophthora-resistant rootstock, which most trifoliate and citrumelo stocks provide.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Improve drainage

This one is designed out at planting. Set the tree high on a raised mound so water drains away fast, keep the graft union, the knob low on the trunk where the fruiting variety was joined to the roots, well clear of the soil, and pull mulch back from the trunk instead of packing it against the bark. Then water in a soak-and-dry rhythm rather than keeping the ground constantly wet. Leaves that wilt and do not perk up after you water are the clue that the roots, not the watering, are the trouble.The organism needs saturated soil, so drainage and planting depth carry this disease and both are set at planting: a raised mound with sharp drainage, the graft union held well above the soil and mulch line, and mulch kept off the trunk. Heavy clay, standing water, a buried union, and overwatering are the classic setups. Where symptoms are already showing, cutting irrigation back is the first correction, since nothing else holds while the soil stays wet.
Resistant rootstock

When you buy, ask for a tree grafted onto a rootstock that resists this rot; most trifoliate and citrumelo rootstocks offer that. You keep the mandarin variety you want and get roots that stand up to it better, and it is settled at the nursery rather than afterward.Rootstock choice is the second at-purchase lever, with most trifoliate and citrumelo stocks carrying Phytophthora resistance. It adds to siting and drainage rather than substituting for them, since saturated soil still drives infection, and it cannot be retrofitted to a tree already in the ground.
Prune out infection

If gum is oozing from a dark patch low on the trunk, correct the drainage and cut the watering back first, or nothing else will hold. Then pull the soil and mulch away from the crown so it can dry, and leave a minor bark lesion open to the air, since a small one can sometimes callus over. Once the rot has girdled the trunk there is no quick cure, which is why the planting steps carry the weight here.Correcting the water and soil condition comes first; exposing the crown and a minor bark lesion to dry can sometimes let it callus over. A girdled crown has no quick cure, and severe feeder-root rot on an established tree is difficult to reverse, so the value here is confined to minor trunk and crown lesions while drainage and planting depth do the real control.

No spray for this one. Prevention is the control.

Alternaria brown spot

D · 03

Symptoms Small brown or black spots with a yellow ring show up on young leaves and shoot tips, and dark, slightly sunken spots appear on small fruit, which may then drop. This one mainly troubles certain tangerine-type mandarins and tangelos (like Minneola and Murcott); satsuma and clementine are not among the types UF lists as susceptible.Small brown-to-black necrotic spots, often ringed by a yellow halo, on young leaves and shoot tips, plus small, slightly depressed dark spots on young fruit that can cause premature drop. It is a mandarin-and-tangerine-hybrid disease: Dancy tangerine and Minneola tangelo are most severely affected, with Murcott, Orlando, Lee, Nova, and Sunburst often hit. Fruit becomes more resistant as it matures, so mostly young fruit is affected. Cause A fungus infects the young leaves and small fruit of susceptible mandarin hybrids, spreading in warm, wet, humid weather. It cannot infect older leaves or older fruit.The tangerine pathotype of the fungus Alternaria alternata infects only young, susceptible tissue and spreads on warm, wet, humid weather, so it is most damaging in the humid Southeast and on the susceptible hybrid cultivars. Older, hardened leaves and older fruit are not infected. Organic treatment If you grow a susceptible type, copper sprays on the new growth during warm, wet weather help protect it, following the label. Spots already there will not heal. On satsuma or clementine you generally do not need to spray at all.On a susceptible cultivar, time copper fungicide applications to protect the new flush and small fruit during warm, wet spells, following label rates; there is no rescue for tissue already spotted. On a tolerant variety no treatment is needed. Prevention The easiest fix is picking the right variety: satsuma and clementine are not among the susceptible types, so choose those in humid areas instead of a susceptible one like Minneola. Otherwise, prune for good airflow, avoid wetting the leaves, and rake up fallen leaves.The strongest control is variety choice: satsuma and clementine are not among the varieties UF lists as susceptible, so plant those in humid regions rather than a highly susceptible hybrid like Minneola or Murcott. Prune for airflow, avoid overhead wetting, and clear fallen leaves. Copper fungicides on the susceptible flush are the fallback where a prized susceptible variety is grown.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Resistant varieties

Variety choice is the easiest fix. The trouble sits on the tangerine-type mandarins and the tangelos: Dancy tangerine and Minneola tangelo are hit hardest, and Murcott, Orlando, Lee, Nova, and Sunburst are often affected. UF does not list satsuma or clementine among the susceptible types, so in a humid region those are the safer pick over a highly susceptible hybrid.Host choice is the strongest control, since this is a mandarin-and-tangerine-hybrid disease: Dancy and Minneola rank most severely affected, and Murcott, Orlando, Lee, Nova, and Sunburst are listed as often affected, while UF's susceptible list does not include satsuma or clementine. In the humid Southeast that one decision largely settles whether any spray program is needed.
Airflow spacing

Prune so air moves through the canopy. The fungus spreads during warm, wet, humid weather, and a canopy that dries out faster gives it less of an opening.Opening the canopy shortens the wetness periods infection depends on, since spread tracks warm, wet, humid weather. On a susceptible cultivar under heavy pressure this supports the variety decision rather than replacing it.
Water at the base

Water the ground under the tree rather than wetting the canopy. Overhead watering adds leaf wetness on top of whatever rain falls, and it is the part of the wet weather you control.Direct irrigation to the root zone instead of over the foliage; the young flush and small fruit are the tissue at risk, and avoidable leaf wetting is the portion of the infection weather within your control.
Garden sanitation

Rake up and get rid of the fallen leaves under the tree. Spots already on leaves or fruit will not heal, so clearing what drops is about lowering how much is around to spread.Clearing fallen leaves lowers what is on hand for the next warm, wet spell. It reduces pressure rather than treating anything, since spotted tissue does not recover.
Copper fungicide

If you grow a susceptible type and want to protect it, time copper sprays to cover the new growth and the small fruit through warm, wet spells, following the label rate. Copper shields tissue that is not yet infected, so it buys nothing on spots already there, and a satsuma or clementine generally calls for no spraying. Copper is hard on fish and other water life and builds up in the soil, so keep spray and runoff away from ponds, streams, and storm drains, and limit repeat use over the years.Copper is the fallback where a prized susceptible cultivar is grown, timed to protect the flush and young fruit during warm, wet weather; it is protective, so landing it on the susceptible stage ahead of infection is what makes it work, and there is no rescue for tissue already spotted. Fruit becomes more resistant as it matures and older, hardened leaves are largely past risk, which is what confines the program to the young tissue. Hold to the label rate, and observe copper's aquatic toxicity and its accumulation at the soil surface with repeat use.

No spray for this one. Prevention is the control.

Greasy spot

D · 04

Symptoms Yellow blotches on top of the leaf with a greasy-looking brown or black blister underneath, followed by leaves dropping, mostly in winter and early spring. It shows up mainly in warm, humid places like Florida and the Gulf Coast.Yellow mottling on the upper leaf surface with a matching blister-like swelling underneath that collapses into a brown-to-black, greasy-looking spot. Infected leaves drop, mostly in winter and early spring, thinning the canopy. It is a warm, humid-climate disease, most troublesome in Florida and the Gulf where relative humidity is high. Cause A fungus infects the undersides of the leaves in warm, humid weather, and it builds up on old fallen leaves under the tree. It is mainly a problem in humid climates, not dry ones.A fungus infects the underside of leaves during warm, humid, wet weather, with spores building on decaying fallen leaves on the ground. High relative humidity and warm nights are what drive it, so it is a Southeastern and Gulf concern rather than an arid-West one. Organic treatment A summer spray of horticultural oil (with copper if needed) controls it on a backyard tree, along with cleaning up fallen leaves. In dry climates you usually do not need to do anything.Horticultural oil, alone or with copper, applied in early to mid-summer gives good backyard control by smothering the developing infection; sanitation of fallen leaves supports it. In arid regions it rarely warrants treatment. Prevention Rake up and remove the fallen leaves under the tree, since that is where the fungus builds, and keep the canopy open for airflow. In humid areas a summer oil or copper spray helps if it is bad.Rake up and remove fallen leaves to cut the spore source, prune for airflow, and keep the tree vigorous. A summer horticultural-oil or copper application, timed to the main infection period, reduces it where pressure is high.

The control ladder

The ladder troubleshoots from the gentlest solution to the strongest. Start with the gentlest option and only move on when and if it doesn't work.

Garden sanitation

Rake up the fallen leaves under the tree and get rid of them. The fungus builds its spores on old leaves rotting on the ground, so clearing them takes away the supply for the next round of infection.Spores build on decaying fallen leaves, so removing the litter cuts the source directly and everything else is built on it. The work earns its keep through a long warm, humid season and matters little where summers stay dry.
Airflow spacing

Prune to keep the canopy open so air moves through it. The fungus gets in through the leaf undersides during warm, humid stretches, and a canopy that dries faster is less hospitable to it.Air movement shortens the humid, wet spells the fungus needs to infect on the leaf underside. High relative humidity and warm nights are the drivers, which keeps this a Southeast and Gulf problem more than an arid-West one.
Copper fungicide

In Florida and along the Gulf, where humidity keeps this troublesome, a summer spray aimed at the stretch when infection is happening cuts it back on a tree under real pressure: copper is the usual material, sometimes with horticultural oil added. In a dry climate you generally do not need to treat at all. Copper is toxic to fish, builds up in the soil, and can burn foliage at too high a rate, so follow the label and keep spray and runoff out of drains and waterways.An early to mid-summer application timed to the main infection period gives good backyard control, copper alone or tank-mixed with horticultural oil, with leaf-litter sanitation still doing the base work. It is preventive, so it goes on ahead of symptom expression, and it rarely warrants use in arid regions. Mind copper's soil accumulation, its aquatic toxicity, and the label rate.

No spray for this one. Prevention is the control.

Verified · 3 sources View

Read the full methodology →

Spot a data point that doesn't match your experience? Submit a correction; accepted corrections earn full author credit on the page.

Mandarin (Clementine)

Will it actually fruit here?

Your mandarin (clementine) year, month by month

Will your winter be cold enough?

One tree is usually enough

Recommended varieties

How big will it get?

The growing journey

Care guide

Yes, on a dwarf rootstock, 15 gallons and up

Soil pH for mandarin (clementine)

Watering

Feeding

Companion planting

When to pick

What to expect

Storing your harvest

Common problems

Pests & diseases

Crop rotation

Common questions

Got a question we missed?

Share a tip

Report a problem

Methodology & sources

Growing notes, weekly.