Gadenin日本語Get the appStart by ruling out the water, not the pests
Nearly every calibrachoa that looks wrong in midsummer is suffering from something you did with the watering can, not from something living on it. Before reaching for a spray, check three things: whether the newest leaves have gone yellow between green veins, whether the basket has been standing in water, and whether it has been allowed to dry out completely at any point. Those three account for the great majority of sick-looking plants.
It also helps to know that the foliage is naturally sticky. Calibrachoa leaves and stems carry glandular hairs and feel slightly tacky at all times. Stickiness on its own is not honeydew and not evidence of insects. Judge pests only by insects you can actually see on the shoot tips and leaf undersides.
| Problem | How to recognize it | Response |
|---|---|---|
| Iron lockout | Newest leaves yellow between green veins, oldest stay green | Chelated iron or ericaceous feed; rainwater if possible |
| Nitrogen hunger | Oldest leaves evenly pale, whole plant thin | Resume weekly liquid feed |
| Root rot | Stem limp and stays limp after watering; dark soft base | Improve drainage; empty saucers; cut out affected stems |
| Drought damage | Band of dropped leaves partway along each stem | Soak the basket in a bucket; trim the bare stems back |
| Aphids | Clusters on the softest shoot tips and buds | Wash off, or spray with insecticidal soap twice, five days apart |
| Thrips | Silvered streaks on leaves, distorted or flecked flowers | Remove worst growth; soap or a suitable spray, repeated |
| Whitefly | Tiny white insects that fly up when the plant is disturbed | Yellow sticky traps plus repeated soap sprays to the undersides |
| Botrytis | Gray fuzz on dead flowers and stems in cool wet weather | Remove affected material; improve air movement; stop overhead watering |
Root rot and the sodden basket
Calibrachoa needs its compost to stay evenly moist but never waterlogged, and the gap between those two states is narrower than for most bedding plants. A basket with a blocked drainage hole, or a container standing in a saucer that never empties, will lose roots within days of warm wet weather. The plant then wilts, and the instinct is to water it more, which finishes it.
The distinguishing test is simple. A plant short of water wilts and recovers within an hour or two of a proper soak. A plant with rotting roots wilts and stays wilted after watering, often with one stem going first while the rest still looks well. Tip the plant out if you are unsure: healthy roots are pale and fibrous and hold the compost together, rotted ones are brown, soft and slide off the core when pulled.
Recovery is possible if you catch it early. Cut away every affected stem back to the crown, repot into fresh free-draining compost with extra perlite, water sparingly until new growth appears, and keep the plant out of full midday sun for a week. If more than half the crown is soft, take cuttings from the clean growth instead and start again.
Aphids, thrips and whitefly
Aphids are the commonest insect on calibrachoa and they go straight for the softest new shoot tips and unopened buds, which is exactly the growth the flowers come from. A heavy infestation distorts new leaves and coats the growth below in sticky honeydew, which then goes black with sooty mold. Small numbers can be washed off with a jet of water; larger ones need insecticidal soap applied thoroughly to the shoot tips and leaf undersides, repeated after five days to catch the young that hatched after the first spray.
Thrips are harder to see and easier to misread. They rasp the leaf surface and leave fine silvery streaks with tiny dark specks of frass, and they feed inside buds so flowers open flecked, streaked or misshapen. They arrive most often in hot dry spells. Cut off the worst-affected growth, spray thoroughly and repeat at five to seven day intervals, because no single application reaches every life stage.
Whitefly cling to the undersides of leaves and rise in a cloud when the basket is knocked. They are more persistent than damaging on an outdoor basket, but they multiply fast under cover, so plants brought into a greenhouse or conservatory need watching. Yellow sticky traps show you the population trend and repeated soap sprays to the undersides keep it down.
Spray in the evening or on a dull day. Insecticidal soap applied to hot leaves in full sun scorches the foliage, and calibrachoa leaves mark easily.
When to give up on a plant
There is a point at which a basket is not worth rescuing, and recognizing it early saves the rest of your plants. A plant whose crown is soft and brown, or one that wilts persistently despite correct watering and shows no new shoots after a fortnight, has lost its roots and will not come back. Take it out of the display rather than nursing it through the summer.
Virus is uncommon but does occur, and it looks like mottled or streaked yellowing that ignores the vein pattern, often combined with distorted leaves and flowers that break color. There is no treatment. Remove and dispose of the plant rather than composting it, and wash your hands and scissors before touching healthy plants.
If a plant is worth keeping for its own sake, take cuttings from clean, unaffected shoot tips before you discard the parent. Cuttings from a healthy shoot of a diseased root system usually establish perfectly well, and they cost you nothing but three weeks.
Record what went wrong, on which basket, and in which week. A note saying that the east-facing basket rotted after a wet fortnight, or that thrips arrived during the first hot spell, is worth more the following year than any general advice, because it is about your own site.