What's eating my pelargonium gibbosum?

Pelargonium gibbosum, the gouty pelargonium, is a succulent-stemmed houseplant grown for its unusual knobbly jointed stems. As an indoor plant it is most susceptible to mealybugs hiding in stem joints and spider mites in dry conditions. Root mealybugs can attack if compost stays wet; fungus gnats breed in overwatered pots.

Cottony white colonies hide in the joints between swollen stem nodes, weakening growth and depositing sticky honeydew. Target each colony with a cotton bud dipped in isopropyl alcohol, then follow up with repeated insecticidal soap sprays every 7–10 days.

Pale stippling and fine webbing on leaves; worst in warm, dry centrally heated rooms where natural predators are absent. Mist around (not on) the plant to raise humidity. Apply neem oil or insecticidal soap spray; repeat weekly for a month.

White powdery insects on roots cause wilting and yellowing despite apparently correct watering; white fluff may be visible at drainage holes. Remove from pot, rinse and inspect roots, and soak briefly in dilute insecticidal soap. Repot into fresh well-draining compost.