Gadenin日本語Get the appThe hazard that injures the gardener
Start with the one problem that harms you rather than the plant. Bergamot peel oil is strongly phototoxic. The furocoumarins in it are inert in the dark and react under ultraviolet light, so juice, zest or oil on skin followed by sunlight causes a real chemical burn: redness and then blistering that appears many hours later, followed by dark brown staining that can persist for months. Because nothing hurts at the moment of contact, almost nobody washes in time, and the connection between the fruit and the burn is usually only made after the fact.
Prevent it rather than treat it. Handle, cut, zest and juice the fruit indoors or in deep shade, always with gloves, and wash hands, forearms, tools and work surfaces with hot soapy water immediately afterwards, since plain water will not remove an oil. Keep any skin that touched the fruit out of direct sun for the rest of the day and ideally overnight. Be particularly careful with children handling windfalls and with visitors who pick up a fruit and squeeze it out of curiosity on a bright day.
If a burn does develop, treat it as the chemical burn it is: keep the area completely out of sunlight, cool it, and seek medical advice if blistering is extensive or if it involves a child. Do not use home pressed bergamot oil on skin under any circumstances, and label any peel infusion or syrup you make with a clear warning, because a jar of fragrant liquid in a kitchen cupboard invites exactly the wrong kind of experiment.
This is a well documented reaction, severe enough that it constrains how bergamot oil may be used commercially. Home pared peel is the full strength material with nothing removed, so the gloves and the shade are not optional refinements.
Scale and the sooty mold that follows it
If an established bergamot is going backwards, look for scale first. These small immobile sap feeders fix themselves to stems, leaf undersides and fruit stalks under a waxy shield and read as limpets or raised brown bumps rather than as anything alive. Run a thumbnail across a suspect bump: a scale lifts off and leaves a damp mark, a natural blemish does not. A heavy population drains the tree steadily, giving thin pale growth, small dull leaves and poor fruit, and container trees are especially vulnerable because a limited root volume has no reserves to absorb the loss.
Timing decides whether treatment works. Scale is almost immune under its shield and is only really vulnerable as crawlers, the mobile juvenile stage that appears in flushes during warm weather. Wrap a strip of double sided tape around a branch to catch them and confirm they are active, then treat with horticultural oil, covering leaf undersides and the canopy interior thoroughly, and repeat two to three weeks later. Oil works by smothering, so coverage matters far more than dose, and anything you miss survives untouched.
The sticky shine on leaves and on the floor beneath the tree is honeydew, and the black film that grows on it is sooty mold. The mold is harmless in itself, does not penetrate the leaf and cannot be treated with a fungicide to any useful effect, because it simply regrows on the honeydew still being produced. Deal with the insect and the mold stops being replenished, then wash the residue off with warm soapy water and a soft cloth. Use the black film as a map: it lands directly below the feeding insects, so the heaviest deposit points you up to the branch to inspect.
| Sign | Likely cause | First action |
|---|---|---|
| Brown limpet-like bumps on stems and leaf undersides | Scale insects | Horticultural oil with thorough underside coverage, repeated in two to three weeks |
| Fine webbing and pale stippled leaves in a warm room | Spider mite, thriving in dry indoor air | Move away from heat sources, raise humidity, spray leaf undersides |
| Sticky shine on leaves and on the floor below | Honeydew from scale, aphid or mealybug | Find and treat the sap feeder; the stickiness is only the symptom |
| Black film over leaves and fruit | Sooty mold growing on honeydew | Treat the insect first, then wash the film off with soapy water |
| White cottony tufts in leaf joints | Mealybug | Dab with a cotton bud dipped in alcohol, then follow with oil |
| Yellowing older leaves with heavy wet compost | Waterlogging and the start of root rot | Stop watering, check the drainage holes, unpot and inspect the roots |
Spider mite, and why winter indoors is the dangerous season
The single most damaging pest of an indoor overwintered citrus is red spider mite, and it is a problem created by the environment rather than carried in from outside. Mites thrive in warm dry moving air, which is precisely what a heated room provides, and they reproduce fast enough that a population invisible in early winter can defoliate a tree by early spring. The early signs are a fine pale stippling across the upper leaf surface, a slightly dusty dull look to the canopy, and eventually delicate webbing in the leaf joints and shoot tips.
The prevention is positional. Keep the tree in the coolest bright frost free space you have rather than a warm room, keep it well away from radiators, heaters and warm air vents, and raise the humidity around it by standing the pot on a tray of damp gravel, with the pot on feet so it is not sitting in water. Cool and humid suppresses mite reproduction; warm and dry accelerates it. Inspect the leaf undersides with a hand lens every fortnight through the winter, since catching the first stippling is the whole battle.
Treatment means physical removal and persistence. Sponge the leaves, especially the undersides, with warm soapy water, and repeat weekly. Spray with a horticultural oil or soap, again covering undersides thoroughly, and repeat at five to seven day intervals for at least three rounds, because eggs are unaffected and hatch after each application. A badly infested tree is often best moved outdoors as soon as nights allow, where humidity, rain and predators do most of the work for you.
Leaf drop, yellowing and root rot in the pot
Sudden leaf drop after a move is the most frequent complaint about potted bergamot and it is a light and temperature shock rather than a disease. A tree taken from full outdoor sun and shut into a dim room loses a proportion of its canopy within a fortnight, because leaves grown in bright light cannot pay their way in poor light and are shed. Prevent it with a staged transition over ten to fourteen days, into a bright cool space rather than a warm dim one. Once it has happened, do not respond by feeding or watering more, both of which make things worse; hold steady, keep the compost only just damp, and wait for the spring flush.
Yellowing has to be diagnosed by pattern before anything is applied. Uniform pale yellow across the whole canopy, worst on the oldest leaves, is nitrogen hunger, common in a pot that has not been fed through a long growing season. Yellow between green veins on older leaves is magnesium, which is very common in containers because hard tap water and regular feeding lock it up. The same interveinal pattern on the newest leaves at the shoot tips is iron, and iron is usually present but unavailable because the compost is alkaline or waterlogged rather than genuinely absent.
Yellowing from the base of the canopy upward on a tree in heavy wet compost is not a feeding problem at all. It is waterlogging, and it precedes root rot. Lift the pot: if it is heavy and the compost surface is dark, sour smelling and slow to dry, stop watering entirely and check that the drainage holes are not blocked by roots or a saucer of standing water. If the tree continues to decline, slide it out and look. Healthy citrus roots are firm and pale; rotted roots are brown, soft and slough their outer layer when pulled between finger and thumb. Cut the dead material away, repot into fresh free draining mix in a pot no larger than necessary, reduce the canopy to match, and water very sparingly until new growth appears.
Fruit problems, and the record that prevents them
Heavy fruit drop shortly after flowering is normal and should not be fought. A bergamot sets far more fruit than a container tree can carry and sheds most of it in two waves, once after petal fall and again at marble size. Drop that continues past that stage, or that takes essentially everything, points to the root ball drying out during flowering and set, to cold nights catching open blossom, or to the tree being moved and shocked at exactly the wrong moment. Split rinds as fruit colors are a watering pattern rather than a disease: a long dry spell followed by a heavy soak swells the flesh faster than the thick rind can stretch. Even watering and a mulch or top dressing prevent it.
Small brown craters and puncture marks in an otherwise good rind are thorn damage from a congested canopy, and they rot from the wound. There is no treatment; the answer is winter thinning so that fruit hangs clear. Note which branch each punctured fruit came from at harvest so that the following winter's pruning is a specific list rather than a general tidy.
Keep a short pest record and it will pay for itself in one season. Note the date you first see scale crawlers, the date and product of each oil application, the date you first find mite stippling each winter and where the pot was standing at the time, and the date and extent of any leaf drop with what changed a fortnight earlier. Leaf drop always lags its cause, and mite always follows a position that was too warm and too dry, so the entry that explains this week's problem is the one written a fortnight ago.