What's eating my euphorbia knuthii?

Euphorbia knuthii, an unusual tuberous-rooted South African Euphorbia kept as a houseplant, is most commonly set back by mealybugs on its slender stems and root crown. Root mealybugs are a particular risk given the fleshy storage root. Spider mites can strike during the dry winter rest period.

White cottony clusters at stem nodes and around the soil line; sticky residue and dieback of new shoots. Dab colonies with an alcohol swab; apply neem oil or insecticidal soap spray to stems and crown; repeat weekly.

Tuberous root failing to push new growth after dormancy; white wax on storage root when unpotted. Carefully unearth the tuber, remove infested soil, wash with soapy water, treat with a systemic drench, and replant.

Pale speckling on slender stems; increased webbing during winter dormancy when indoor air is very dry. Wipe stems with a damp cloth, apply neem oil or miticide, and keep surrounding air humidity moderate.