What's eating my hoya griffithii?

Hoya griffithii, like most hoyas, is most troubled by mealybugs and spider mites — sap-suckers that thrive in warm, dry indoor conditions. Mealybugs are the most common threat. Check leaf axils and stem joints regularly. Aphids and fungus gnats can also appear, especially in humid rooms with damp compost.

White cottony clusters in leaf axils and stem joints; sticky honeydew residue; stunted, distorted new growth. Dab individual colonies with isopropyl alcohol on a cotton swab; spray plant with neem oil solution weekly for 3–4 weeks; isolate infested plants.

Fine pale stippling on leaves; silky webbing on undersides and between stems; leaves may yellow and drop in heavy infestations. Raise humidity around the plant; wash leaves with a damp cloth; apply insecticidal soap or dilute neem oil spray, repeating every 5–7 days.

Soft green or black insects clustered on new shoots; curled or puckered young leaves; sticky honeydew attracting sooty mould. Knock off with a strong jet of water; apply insecticidal soap spray; introduce beneficial insects such as ladybirds in a conservatory setting.

Larvae in compost damage fine roots; adult gnats are a nuisance around the plant; yellowing and wilting can follow root damage. Allow the top 2–3 cm of compost to dry fully between waterings; apply Bacillus thuringiensis var. israelensis (Bti) soil drench; use yellow sticky traps for adults.