White fluff where the leaf meets the stem
Mealybugs. What the fluff is, why they hide in joints and under leaves, and the four week routine that clears them properly.
This one is worth acting on today rather than at the weekend. A week of waiting changes what is left to save.
What it usually is
1 Mealybugs
| How to tell | Small oval insects, two to four millimetres, coated in white waxy fluff, tucked into leaf joints, under leaves and along stems. They move slowly if prodded, which distinguishes them from mildew or fluff. There may be sticky residue below them and a sooty black mould growing on it. |
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| The fix | Dab each insect with a cotton bud dipped in surgical spirit, which dissolves the wax and kills it on contact. Then wash the whole plant with soapy water, undersides included. Repeat weekly for four weeks, because eggs hatch over that period. |
2 Root mealybugs
| How to tell | A plant that declines steadily with no pest visible above the compost. Tip it out: root mealybugs look like white fluff or a white powdery deposit on the roots and the inside of the pot. |
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| The fix | Wash all compost off the roots, cut away badly infested roots, and repot into fresh compost in a clean or new pot. Throw the old compost away. Check the plants that stood next to it. |
3 Brought in on a new plant
| How to tell | The first infested plant arrived recently, and the infestation is heaviest on the growing tips and in the tightest joints where it was not visible in the shop. |
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| The fix | Quarantine every new plant for three weeks and inspect the joints and undersides weekly before it joins the others. This is the single habit that prevents most pest outbreaks indoors. |
Through the year. Indoors they breed all year, and fastest in warm rooms. An outbreak that seems to appear in January usually started in October and was hidden in the joints.
Mealybugs are marked urgent here for the same reason as spider mites: not because they kill quickly, but because they spread while you are deciding. A female lays several hundred eggs in a waxy sac, the crawlers that hatch are small enough to be almost invisible, and they walk to the next plant along a touching leaf.
The white fluff is wax, secreted by the insect to keep itself from drying out, and it is also what makes them hard to kill. A soapy wash runs off it, and so does most of what you might spray. That is why the surgical spirit on a cotton bud is the standard treatment: alcohol dissolves the wax and the insect dies immediately. It is slow, fiddly work on a large plant and there is no shortcut that works as well.
The routine is: go over the plant with the cotton bud, taking every visible insect and every white smear in a joint, then wash the whole plant, both sides of every leaf, with tepid soapy water. Then do it again in a week. And again, and again, for four weeks in total. The repetition is what matters, because the eggs are protected and hatch over that period. One thorough treatment always looks like success and always fails.
While you are at it, look at three other places. The undersides of leaves, where they gather along the veins. The very tip of the growing point, folded inside the newest leaf. And the pot: run a finger round the rim and just under it, which is where they cluster when a plant is crowded.
If a plant is declining with no insect anywhere on it, tip it out and look at the roots. Root mealybugs are the same insect living below the compost, and they show as white fluff on the roots and a white deposit on the inside of the pot. That plant needs its roots washed clean, fresh compost, a different pot, and the old compost in the bin.
A heavily infested plant that is not precious is often best thrown away. Four weeks of treatment on a plant you were tired of anyway is four weeks of risk to the rest of the shelf.
Entries that name it
What the journal says about this symptom on each plant.
| Bird of paradise | Mealybugs where the leaf stalks meet the base. Dab each one with a cotton bud dipped in alcohol, part the stalks and check right down to the compost, and repeat weekly. |
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| Echeveria | Mealybugs between the leaves of the rosette. Dab each with a cotton bud dipped in alcohol, check the roots too, and repeat weekly until nothing new appears. |
| Jade plant | Mealybugs sheltering where the leaves meet the stem. Dab each one with a cotton bud dipped in alcohol, check weekly, and repeat until a fortnight passes with nothing new. |
| String of pearls | Mealybugs hidden where the strands meet the crown. Dab each one with a cotton bud dipped in alcohol and check weekly until a fortnight passes with nothing new. |
Questions from the margin
- What is the white fluff on my plant?
- Mealybugs. The fluff is wax the insect secretes to stop itself drying out, and it is also what makes them hard to kill, because sprays and soapy water run off it. Look in the leaf joints, under the leaves and around the rim of the pot.
- How do I get rid of mealybugs?
- Dab each insect with a cotton bud dipped in surgical spirit, which dissolves the wax and kills it on contact, then wash the whole plant with soapy water. Repeat weekly for four weeks, because the eggs are protected and hatch over that period.
Checked against RHS, Mealybug; Royal Botanic Gardens Kew, Glasshouse pest management.