Both the 1cm-long black adults and 1cm-long plump, white, legless, brown-headed larvae are a problem. The latter hide in the soil, and feed on roots (severing them) and bore into tubers from autumn to spring. Container plants are most at risk. The adults have six legs and a pair of antennae, moving in the open at night, chewing the edges of leaves. This isn’t itself a problem, but the fact that each adult is a female, laying almost 1,000 eggs in summer, is alarming.
Holes and notches chewed out of leaf edges, roots damaged, plant suddenly wilts and dies.
Find it on
many plants, container-grown plants are especially vulnerable
Go out at night with a torch and pick off the adults. To kill the larvae, in August/early September treat the compost with a predatory nematode, which is sold by mail order.