Hoya Pests and Problems: Mealybugs, Scale and Rotting Stems

Where the trouble hides on a hoya

A hoya has thick waxy leaves that shrug off most things, so pests concentrate in the few places that are soft and sheltered: the leaf axils, the growing tips, the undersides of the leaves and, above all, the flower spurs and buds. Those are also the places you cannot see without deliberately looking.

Because the stems tangle and the plant is usually against a window or high on a shelf, an infestation is often three weeks old by the time it is obvious from across the room. Make a habit of turning a few stems over whenever you water.

Mealybugs are the one that matters

Mealybugs look like small blobs of white cotton wool wedged into a junction. They feed on sap, excrete a sticky honeydew that goes black with sooty mold, and they breed fast in a warm room all year round. On a hoya they favor the leaf axils and, infuriatingly, the flower spurs, which is exactly where you cannot afford to be rough with the plant.

1. Deal with a few by hand Dip a cotton bud in surgical spirit and touch each insect. It kills on contact. Go over the whole plant, axil by axil, and repeat every four or five days for three weeks to catch the ones that hatch after you started.
2. Clean the spurs carefully Do not scrub a flower spur or pick at it with a fingernail. Use a cotton bud and take your time. The spur is the flowering wood and damaging it costs you the flowers.
3. Wash a heavy infestation Take the plant to a sink and rinse it with tepid water, supporting the stems. Then treat with an insecticidal soap or a horticultural oil, covering the undersides. Repeat twice at weekly intervals.
4. Check the roots too If the plant keeps reinfesting after a thorough clean, slide it out of the pot. Root mealybugs sit as white powder on the rootball and no leaf spray will ever reach them. If you find them, wash the roots clean and repot into fresh mix and a clean pot.

Isolate any plant you are treating. Mealybugs walk between plants that touch, and a hoya trailing across a shelf touches everything.

Scale, aphids and mites

These three are less common but all turn up. Identify by where they sit and what the leaf does, and treat early: on a slow-growing plant like a hoya, damaged leaves stay damaged for years.

Rot is the thing that actually kills hoyas

Far more hoyas die from wet compost than from any insect. The roots are fine and epiphytic, adapted to sitting in bark and moss on a branch with air all around them, and they suffocate quickly in a dense mix that stays saturated.

The warning signs run in a sequence. Leaves go soft and slightly wrinkled while the compost is still wet, which people misread as thirst and water again. Then a stem goes yellow and translucent near the base, then black, and then the whole plant collapses in a couple of days.

1. Check the compost before you diagnose anything Wrinkled soft leaves with wet compost is rot. Wrinkled soft leaves with dry compost is thirst. The symptom is identical and the treatments are opposite, so never skip this check.
2. Act the day you suspect it Take the plant out of the pot. Healthy hoya roots are firm and pale. Rotted roots are brown, soft and slide out of their own skin when you pull. Cut every soft root away.
3. Salvage cuttings immediately If more than half the roots have gone, do not try to save the plant. Take healthy stem cuttings from the top growth straight away and root those. A hoya rescued too late takes the cuttings down with it.
4. Fix the cause Repot into a chunky bark based mix in a pot no bigger than the rootball, and empty the saucer every time. Going back into the same dense compost guarantees a repeat.

Marks on the leaves that are not pests

Several hoya complaints have nothing to do with anything living, and treating them with a spray only adds stress.

Write down the date you first see any pest and the date you finished treating. Mealybugs come back on a cycle, and a note of last autumn's outbreak tells you when to start checking this year.