Vine weevils are a devastating plant pest – suddenly otherwise healthy looking plants wilt and collapse and no amount of watering will help them recover. The reason? The vine weevil grubs have eaten all the roots.
Vine weevil grubs are particularly rampant in containers, but they also attack plants in borders and beds, where dealing with them is far more difficult. The real danger is the underground grub - you can’t see what they’re doing until maybe it’s too late.
Baby vine weevils grow from little eggs laid in the plant’s roots - which are very difficult to see. They hatch into 10mm long ‘C’ shaped grubs with cream coloured bodies and brown heads. The little vandals, unseen, simply munch away at the root system until either they are caught or the plant first yellows, then wilts and collapses through lack of sustenance.
Adult vine weevils are dusty grey/black flightless beetles. They are all female and each can lay up to 1,000 eggs in a season. Eggs are laid during the summer and early autumn ready to become grubs in spring the following year. These beetles do most of their eating at night and restrict themselves to nibbling away at the edges of leaves. The results are unsightly but not life-threatening to the plant. However the energy they get from eating ensures that the eggs will be laid. So they can’t be ignored.
Treatment and control
Adult vine weevils are pretty resistant to sprays. It is best to physically remove them. Collect them, by torchlight, at night whilst they are feeding. Place a newspaper, a tray or something else that will catch these flightless beetles and ‘knock’ the plant to dislodge them. Pick them up, squash them and bin them.
Drench the compost
It is possible to kill the adult larvae that feed on plant roots by drenching the compost in which ornamental plants are growing with a systemic insecticide.
Treating edible crops
There are no recommended insecticides approved for treating edible crops.
Introduce pathogenic nematodes. These are little parasitic worms which will do no harm to the plant but which will kill the vine weevil larvae with a fatal disease. As with most biological controls the conditions need to be absolutely right for the treatment to work.