Curry Leaf

Root rot is not one organism but a group of soil fungi and water molds - Pythium, Phytophthora, Fusarium, Rhizoctonia and others - that sit harmlessly in most soils and only turn destructive when the ground stays saturated. Waterlogged soil drives the air out, the roots suffocate, and the weakened tissue is invaded and goes soft, brown, and stringy. Because the damage is underground you usually see it first as something that looks like drought: wilting, yellowing, stunting, a plant that does not respond to being watered. Overwatering, heavy compacted ground, a low spot that collects runoff, a pot with no drainage or a saucer left standing full, and cold wet soil in winter are the usual causes. Once roots have actually rotted there is no cure - this is a problem you prevent rather than treat.

Watch for: Wilting in the middle of the day on a plant whose soil is damp - the classic tell, and the reason people water a rotting plant and finish it off. Leaves yellowing from the bottom up, dull off-color foliage, and growth that stalls for no visible reason. Whole shoots, or one side of the plant, collapsing while the rest still looks fine. Soft, dark, or mushy tissue at the base of the stem or at the crown, sometimes with a sour smell. Lift a failing plant and look at the roots: healthy ones are firm and pale, rotted ones are brown or black and slimy, and the outer layer slips off between your fingers leaving a thread of core behind. Seedlings that topple over at soil level are the same problem, called damping-off.

Prevent: Drainage is the whole defense. Match the plant to the site first - something that wants sharp drainage will not survive heavy clay or a low, water-collecting spot however well you tend it. Where the ground is heavy, plant on a raised bed, berm, or slope, or grow in a container. Set plants at the depth they were already growing, since burying the crown or the root flare is a common cause of rot, and keep mulch pulled back a few inches from the stem base instead of piled against it. Water the soil rather than the calendar: check that the top inch or two is dry before watering again, cut back hard in cool weather and winter dormancy, and never leave a pot standing in a full saucer. Do not plant or dig in soggy ground, and go easy on rich amendments for plants that want it lean. Rotate annual crops, and start with clean healthy plants and fresh mix.

Treat: There is no cure for tissue that has already rotted, so act on the conditions rather than looking for a spray. Stop watering at once and fix the drainage - open up compacted soil, or move the plant to a raised, sharply drained position or a container. Lift a badly affected plant, cut away every soft dark root and rotted section with a clean blade back to firm pale tissue, and replant only the healthy parts into fresh free-draining soil or mix. Often the better move is to give up on the plant and save its offspring instead: cuttings, offsets, or divisions taken from firm healthy growth root readily and give you a clean start. Bin the rotted material rather than composting it, and correct the drainage before you replant, because the rot comes straight back in the same wet spot.

The commonest way this plant dies, and almost always self-inflicted. A semi-dormant winter plant in short days uses hardly any water, and a well-meaning owner watering a leafless tree back to health drowns it. Water perhaps once every three or four weeks indoors, use a gritty free-draining mix in a pot that actually drains, and never leave it standing in a saucer of water.

Spider mites are not insects but tiny sap-feeding arachnids, smaller than a grain of salt, and you almost always notice the damage before you notice them. They live on the undersides of leaves and drain the cells one at a time, which is why the leaf goes finely stippled with pale dots before it bronzes and dries. They breed explosively in hot, dry, dusty, still air - a generation can pass in a week at high temperature - so a barely visible population becomes a webbed, bronzed plant within a fortnight. Drought-stressed plants and plants wintered indoors in dry heated air are the classic hosts. Broad-spectrum insecticides make matters worse rather than better, because they kill the predatory mites and lady beetles that normally hold mites in check.

Watch for: Fine pale stippling or speckling across the upper leaf surface, as though the color had been sandblasted out of it, and later a dull bronze or rusty cast over the whole leaf. Delicate webbing across leaf joints, shoot tips, and undersides - that comes with a heavy infestation and means you caught it late. Leaves that dry, curl, and drop early while the plant looks thirsty no matter how much you water it. Hold a leaf over a sheet of white paper and tap it: the specks that fall and then start walking are mites. With a hand lens, look on the undersides for the mites themselves, pale or reddish, and their round translucent eggs. Damage that shows up first on the hottest, dustiest, most sheltered side of a plant, or on a pot sitting near a radiator indoors.

Prevent: Do not let plants get drought-stressed - that is the single strongest trigger, and a plant watered steadily through heat is far less likely to have a mite problem at all. Hose the foliage down, undersides included, during hot dry spells: it knocks mites off, washes away the dust they thrive in, and raises the humidity around the plant for a while. Indoors and under cover, keep the air from going hot, dry, and stagnant, wipe or rinse the leaves occasionally, and keep pots away from radiators and heating vents. Inspect any plant carefully before you bring it indoors for winter or set it among others, since mites almost always arrive on something else. Avoid broad-spectrum insecticides: they wipe out the predatory mites, lacewings, and lady beetles that do most of this work for you, and reliably leave you with a worse outbreak than you started with.

Treat: Start with water. A strong jet aimed at the leaf undersides, repeated every few days for a couple of weeks, knocks populations down and breaks the cycle - on many plants that alone ends it. On anything that regrows quickly, shearing back badly infested growth resets the plant to clean foliage. If it keeps building, spray insecticidal soap or horticultural oil directly onto the undersides where the mites actually live, and repeat every five to seven days for three rounds: contact sprays do not kill the eggs, so a single application always fails. Anything you spray must be labeled for the plant you are treating - follow the label and observe its pre-harvest interval on anything you eat. Predatory mites are an effective release in a greenhouse or on an indoor plant. Above all, correct the heat, dust, and drought stress that caused it, or the mites simply come back.

The main pest of an overwintered curry leaf, and close to inevitable on a plant standing in dry heated air all winter. Fine pale stippling on the leaflets and webbing in the leaf joints are the signs; a plant already shedding leaves for dormancy hides the damage until it is bad. Rinse the whole plant in the shower every few weeks, keep it off the radiator, and inspect weekly from November.

The Asian citrus psyllid is a tiny mottled brown sap-sucking insect, roughly the size of an aphid, that feeds only on citrus and its relatives in the Rutaceae family. Adults sit at a distinctive nose-down angle on new shoots, and the yellow-orange nymphs cluster on the unopened flush producing curled waxy tubules of honeydew. The feeding itself twists and distorts new growth but rarely kills a plant. Its real significance is that it is the vector of citrus greening (huanglongbing), the incurable bacterial disease that has devastated citrus across Florida, Texas and parts of California. A psyllid population on any Rutaceae host inside a quarantined area is a reservoir that carries the disease to nearby citrus, which is why the movement of these plants and their leaves is federally regulated. It breeds only on tender new growth, so populations track the flush cycle rather than the calendar.

Watch for: Tiny brown-mottled insects about an eighth of an inch long perched nose-down at a sharp angle on the tips of new shoots - the posture is the giveaway, and no other pest of these plants holds it. Yellow-orange nymphs packed into the unopened flush, along with white waxy curls and tubules of honeydew that look like tiny springs. New leaves that emerge twisted, notched, curled or stunted, with a sticky shine and later black sooty mold on the growth below. A cloud of small insects that jump and fly when you disturb a flush. Ants working the shoot tips. Check every new flush from the moment it pushes, since that is the only growth the insect breeds on, and use a hand lens - the adults are easy to mistake for aphids at a glance.

Prevent: Buy plants only from a licensed local nursery, and never accept or move these plants, cuttings or leaves out of a quarantined area - that is how the insect and the disease travel between regions, and in most quarantined states it is against the law. Inspect every new flush through the growing season, since the insect breeds only on tender new growth, and water and feed steadily rather than in bursts so the plant pushes fewer and less concentrated flushes to defend. Do not plant a preferred host right beside your citrus. Leave the lady beetles, lacewings, syrphid larvae and the parasitic wasp Tamarixia radiata alone, because they do most of this work where broad-spectrum sprays are not used. Report a suspected find to your state agriculture department or extension office; regional programs depend on early detection and will often survey and advise for free.

Treat: Act on the flush, not the calendar. Knock light populations off with a hard jet of water, and rub out colonies on a small plant by hand. Horticultural oil and insecticidal soap kill nymphs and adults on contact and are the right choice on anything you eat, but they must coat the shoot tips thoroughly and be repeated every seven to ten days while the flush is soft. Prune off heavily infested flushes and bin them rather than composting them. Where the disease is present, area-wide programs may call for a soil-applied systemic or a coordinated spray schedule - follow your state's guidance rather than improvising, and use only products labeled for the plant, observing the pre-harvest interval on anything you harvest for the kitchen. Removing a badly infested plant that sits beside healthy citrus is sometimes the responsible answer. Report finds so local programs can track spread.

This is the single most important thing to know about growing curry leaf in the United States. Research has found it MORE attractive to the psyllid than citrus itself, and it is used deliberately as a trap plant for that reason - while being immune to the greening bacterium, so the tree stays healthy while breeding the insect that infects your lemon tree. Keep it well away from citrus in quarantined areas, scout every flush, and never move plants or leaves across state lines.

Scale insects are sap-suckers that spend most of their lives immobile, fixed to a stem, twig, or leaf underside beneath a waxy or shell-like cover. They look far more like bumps, blisters, or crusty encrustations than like insects, which is why an infestation is usually well established before anyone notices it. Soft scales excrete large amounts of sticky honeydew that drips onto everything below and grows a black sooty mold - and those blackened leaves are often the first thing a gardener actually sees. Armored scales produce no honeydew but sit under a hard shield that protects them from most sprays. They spread as tiny mobile crawlers in the weeks after hatching, which is the only stage that moves and the only stage that is easy to kill. Populations build on stressed plants, on crowded shaded growth, and above all on plants kept indoors in dry, still air over winter.

Watch for: Rows of small brown, tan, black, white, or waxy bumps along stems, twigs, leaf midribs, and leaf undersides that do not brush off but can be scraped loose with a fingernail. A sticky shine on the leaves - and on the floor, table, or path beneath the plant - that later turns black with sooty mold. Ants running steadily up and down the stems, since they farm and defend scale for that honeydew; often the first sign anything is wrong. Yellowing leaves, weak thin growth, and dieback of individual branches or canes that are heavily encrusted. On fruit crops, scale covers and sooty mold directly on the fruit. Check the leaf undersides and the shaded inner wood, which is where colonies build up unseen.

Prevent: Inspect. Look over leaf undersides and stems regularly - on a crop you pick, every harvest is a scouting chance - and check every new plant thoroughly before you buy it, plant it, or set it beside anything else, because scale almost always arrives on a plant rather than flying in. Quarantine new houseplants for a few weeks. Keep plants unstressed and not over-fertilized, since soft, forced growth is what populations build on. Prune for airflow and light to open up the shaded inner growth where scale hides, and prune out heavily infested wood as routine maintenance - on anything that gets a hard annual pruning, that alone removes most of any buildup. Leave the lady beetles, lacewings, and parasitic wasps alone, since they normally keep scale down to nothing, and keep ants off the plant where you can, because ants protect the colonies from those predators. Indoors, avoid hot, dry, still winter air.

Treat: Horticultural oil is the main control: it works by smothering, so it has to coat the insects thoroughly - stems, twigs, and leaf undersides - and it usually needs repeating, because the waxy covering shields them and no single pass reaches everything. On deciduous woody plants a dormant-season oil smothers the overwintering stage while the leaves are out of the way, and timing a growing-season spray to the crawler stage, when the young are mobile and uncovered, is far more effective than spraying settled adults. On a small plant or a light infestation, scrub or wipe the scales off by hand, or dab them with a cotton swab of rubbing alcohol. Prune out and destroy badly encrusted wood rather than trying to save it. Wash off the sooty mold once the scale is gone - it lives on the honeydew, not on the plant, and stops once the supply does. Anything you spray must be labeled for the plant, and oils can burn delicate foliage, so test first.

Common on curry leaf and easy to miss, since the bumps sit along the thin leaf stalks and stem joints where they look like part of the plant. Sticky leaflets and a black film are usually what you notice first. Wipe small colonies off with an alcohol swab and use horticultural oil on larger ones - the leaves are eaten, so stick to oil and soap and rinse harvested sprigs well.

Soft, slow-moving sap-suckers that coat themselves and their egg masses in a white waxy fluff, so a colony looks like scattered specks of cotton wool rather than like insects. They wedge into the places hardest to see and hardest to spray - leaf axils, crevices, stem joints, leaf undersides, the base of the plant, and sometimes the roots - and feed there for weeks, weakening growth and excreting sticky honeydew that blackens with sooty mold. Ants farm them for that honeydew, carry them from plant to plant, and drive off the predators that would otherwise control them. Populations explode in warm, dry, still air, which is why indoor and greenhouse plants suffer worst.

Watch for: White cottony masses tucked into leaf axils, crevices and stem joints, which smear rather than brush off. A sticky shine on the leaves and on the surface beneath the plant, later blackened with sooty mold. Ants running steadily up and down the stems - often the first thing anyone notices. Yellowing, stunted or distorted growth with no other obvious cause. On a plant that has been treated repeatedly and keeps declining, check the roots, because root-dwelling mealybugs are easy to miss entirely.

Prevent: Inspect new plants thoroughly before you buy, and quarantine anything you bring indoors for a few weeks - mealybugs almost always arrive on another plant rather than flying in. Check leaf axils and crevices every few weeks on anything grown under cover, since a colony found early is trivially dealt with. Control the ants that protect and spread them; a sticky barrier on a pot rim or a stem does a lot of work. Keep plants unstressed, avoid heavy nitrogen feeding, and do not leave them standing in hot, dry, stagnant air.

Treat: Deal with small colonies mechanically: dab them with a cotton bud dipped in rubbing alcohol, wipe them off with a damp cloth, or wash the plant down with a firm jet of water aimed into the crevices where they hide. For anything larger, spray insecticidal soap or horticultural oil directly onto the insects, which means getting into the axils and undersides where they actually live, and repeat every seven to ten days for at least three rounds, because the waxy coat protects them and contact sprays do not kill the eggs. Cut out badly infested growth rather than nursing it, deal with the ants at the same time or the colony rebuilds, and test any oil first, since it can burn foliage in heat.

White cottony tufts wedged into the leaf axils and where the pinnate stalks meet the stem, especially on plants kept indoors. Because the harvest is foliage, treat early and by hand with an alcohol swab or a strong rinse rather than letting a colony build to the point where you would want a spray.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Ride the soft spring and autumn flushes and distort the new leaflets. Rarely serious on curry leaf, but they matter as a scouting habit: the same flush inspection that finds aphids is the one that finds the Asian citrus psyllid, and the two are easy to confuse at a glance. Wash colonies off with a hard jet of water and check what you found with a hand lens.

A black, soot-like fungal coating that grows on the sticky honeydew excreted by aphids, scale, mealybugs, and whiteflies - it doesn't infect the plant directly but coats leaves and fruit in a black film that blocks light and disfigures them (a particular nuisance on makrut lime, grown for clean leaves).

Watch for: A black, dusty or crusty coating on leaves, stems, and fruit (that can be rubbed or washed off), always accompanying a honeydew-producing pest above it.

Prevent: Control the underlying sap-sucking pest (aphids, scale, mealybugs, whiteflies) - no honeydew, no sooty mold. Encourage beneficial insects and treat the pest, not the mold.

Treat: Treat the underlying scale/mealybugs first; then wipe or wash the sooty film off leaves with mild soapy water. It doesn't infect the plant, but heavy coating blocks light and weakens it.

A cosmetic but genuine nuisance here because the leaves are the crop - a black film on the leaflets means you are washing every sprig before it goes in the pan. It is a symptom, so find the scale, mealybugs, aphids or psyllids producing the honeydew above and treat those; the mold weathers off once the supply stops.

A tiny moth whose larvae mine winding, silvery serpentine tunnels just under the surface of new citrus leaves, curling, twisting and distorting them. It attacks only the tender new-growth flushes, never mature leaves or fruit, so on an established tree it is essentially cosmetic - but it can stunt a young tree, and the wounds it leaves in the leaf provide entry points for citrus canker bacteria, which is its real significance.

Watch for: Silvery, squiggling serpentine trails inside new leaves, and curled, twisted, distorted new growth on the flushes. Mature leaves and fruit are untouched.

Prevent: Established trees tolerate it, so the aim is to give it less to work with: avoid over-fertilizing, which pushes out the excess soft flushes it feeds on, and stop feeding by late summer so there is no tender autumn flush to mine. Encourage the parasitic wasps that control it, and protect young trees and new grafts, whose growth actually matters.

Treat: Largely cosmetic on an established tree - prune off heavily mined flushes if you want to, and otherwise leave it alone rather than spraying for appearance. Horticultural oil applied to new flushes deters egg-laying. Systemic controls are used mainly on young trees or where canker pressure is high.

Turns up on outdoor curry leaf in the citrus-growing South and West, mining silvery trails in the soft new flushes. Cosmetic on an established plant and not worth spraying, but it disfigures leaflets you were going to cook with, and it can set back a small container plant whose entire canopy is new growth. Pinch off badly mined sprigs.