What's eating my emerald spike moss?

Emerald Spike Moss (Selaginella martensii) is most vulnerable to spider mites, which exploit any drop in humidity to colonise its delicate, moss-like stems. Fungus gnats breed readily in its perpetually moist growing medium, and mealybugs can hide deep in the dense foliage. High humidity is the best all-round defence.

Webbing across stem tips, bronzing or bleaching of the bright green foliage, and stem dieback starting from the tips. Maintain humidity above 60% at all times. Spray the plant with water to dislodge mites, then apply insecticidal soap or neem oil every 7 days for three weeks.

Adult gnats flying around the pot; larvae in the top layer of moist substrate damaging fine roots, leading to yellowing and weak growth. Top-dress with horticultural sand to create a dry barrier, or use yellow sticky traps for adults. Drench the growing medium with a Bti (Bacillus thuringiensis israelensis) solution to kill larvae.

White cottony deposits lodged deep in the dense stems; slow yellowing and weakening of affected branches. Dab accessible colonies with an alcohol-soaked cotton swab. For dense infestations, apply a diluted neem oil spray across the entire plant surface, repeating every 10 days.