What's eating my rieger begonia?

Rieger begonias (Begonia × hiemalis) are susceptible to vine weevil grubs eating roots and rhizomes, mealybugs in leaf axils, and thrips distorting flowers. Botrytis (grey mould) is triggered by pests that wound tissue. Cool, well-ventilated conditions help; avoid overhead watering. Inspect roots at the first sign of wilting.

Plant wilts suddenly despite adequate watering; white C-shaped grubs destroy roots and rhizome when the pot is tipped out. Apply Steinernema kraussei nematode drench to moist compost; check roots at repotting; pick off adults (nocturnal) by torchlight.

Silver-streaked or bronzed petals and distorted flowers; tiny dark specks (frass) visible on petals; flowers fail to open fully. Remove affected flowers; introduce predatory mite Amblyseius cucumeris; blue sticky traps monitor adult numbers; apply neem oil or spinosad spray.

White waxy fluff in leaf axils and stem joints; leaves wilt and yellow even with correct watering. Treat with alcohol swab and neem oil; isolate plant; remove and discard badly infested shoots.