Springrowth Garden Centre: Treating vine weevil in Derry

This week, we will cover one of the worst insects you could have in your garden; the vine weevil.

By Cyril Quinn
Thursday, 5th May 2022, 3:49 pm

I didn’t want to bombard readers with too many posts about garden pests but I think this is an important one.

Most people won’t know what they are unless they’ve been unfortunate enough to come across them.

They are the most harmless looking insect but can cause the most damage to your plants because they attack above and below the ground.

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Closeup on the Black vine weevil, Otiorhynchus sulcatus sitting on a piece of wood

The adults are nocturnal and would normally only come out to feed at night.

They can be spotted during the day if they have been disturbed from their hiding places, which include underneath pots and the underside of leaves and branches.

They have a dark grey body with pale yellow blotches and they move very slowly.

They will not move at all if they see you.

One of the tell-tale signs that you have vine weevil are notches eaten out of leaves starting from the outer edge of the leaf.

Other signs that you have these little terrorists are when your plants start to wilt and discolour and just look like they are in poor health for no obvious reason. The reason for this is that the larvae are in the soil and they actually do more damage than the adults.

An adult can lay up to a thousand eggs, not all of these will hatch but a large percentage will survive. The larvae grow up to about 10mm long and are a creamy white ‘C’ shaped grub with a light brown head.

When they hatch they will start to eat the fine root hairs of your plants and as they grow, they will eat more fleshy roots and will even strip the bark around the stem at soil level on some softer plants.

Cyril and Alison Quinn, proprietors of the Springrowth Landscape and Garden Centre, Springtown Industrial Estate. DER2115GS – 028

Vine weevil seem to have a preference for the nice soft fleshy roots of herbaceous plants such as Hosta, Astilbe, Polyanthus, Heucheras but I have seen them in pots of Laurel and Leylandii hedging too so they will just eat whatever it takes to survive.

There are a few ways to control vine weevil; Chemically - there are a few products available such as ‘Provado’ which will kill the larvae.

Biologically - ‘nematodes’ which are a parasitic worm which enter the larva and feed on them until the larva dies.

Physically - if you think you have vine weevil larvae in your pots, you can tell by the unhealthy looking plant or by tugging it and if it seems to be loose in the soil then they may be there eating away.

Lift the plant out of the pots and shake the soil where they will be clearly visible. You can’t see the eggs as they are microscopic.

If you haven’t the heart to kill the larva or are squeamish, collect them and put them on a bird table, the robins love them and will gulp down the lot. Sometimes the plant can be saved if you catch it in time and there is still enough root left to feed the rest of the plant, but I would use a product such as Provado to make sure to kill any I may have missed too.

The adults have natural enemies too such as ground beetles, or clocks as they are locally known, so don’t be tempted to step on these as they are a beneficial insect to have about the garden and are carnivorous so they won’t damage your plants.

You can make traps for the adults, a simple trap is a toilet roll tube filled with screwed up paper, leave a few of these around your greenhouse or garden and shake them out in the mornings. Earwigs will hide in these too!