The hidden killer lurking beneath your pot plants

The ‘bomb’ in question is a tiny root-eating grub which can cause immense damage while gardeners ponder what’s causing pot plants to yellow, wilt and keel over.

Adult vine weevils lay eggs in soil from March to September, which hatch into white, C-shaped grubs that feed voraciously.

All Otiorhynchus sulcatus adults are female and each can lay many hundreds of eggs from April to September. The eggs are brown and less than 1mm (about 1/16in) in diameter, making them very difficult to see in the soil.

You know you’ve got vine weevils in the garden if you spot small, irregular notches missing around the outside of leaves. This is caused by adult beetles, which feed at night on a whole host of plants including euonymus, bergenia and hydrangea. This damage is largely cosmetic.

But plants grown in pots are sitting targets for vine weevil grubs, which live beneath the soil and eat the roots. Cactus, succulents, cyclamen (pictured) and begonia and all very vulnerable.

Ornamental plants grown in containers can be treated with a liquid drench applied to the compost. Several insecticides will protect against the grubs for a couple of months; treatment in mid- to late summer will control the young larvae and prevent autumn damage.

Another method is to use nematodes that are a natural enemy of vine weevils.

The larvae remain in the soil until they emerge as adults. Most die in late autumn but those in houses can survive.

You have been warned.