Often rated as the number one pest in gardens, vine weevils are certainly a creature most of us dread finding. For those who use a lot of containers in their garden, this really is the pest that nightmares are about.
The vine weevil adults are beetle like creature just less than 1cm in length. They are a matt black with delicate tan brown flecking on their backs. They have antennae that are elbowed, but rather unusually they cannot fly. To compensate for this they are unbelievably skilled and agile climbers, a trip from the garden up to a window box on the first floor seems easy.
The damage the adults do is generally not of great significance to an otherwise healthy plant: they take notches out around the edges of leaves, usually concentrating on the lower leaves as these are most easily accessible. They cause most obvious damage in late spring and early summer, but will not kill or even seriously weaken it.
It is the young or grub stage, which causes problems as they eat roots, remove the bark from large tough roots and burrow in to tubers. In fact you may well only realise that the grubs are doing damage when all of a sudden plants suddenly start to wilt and die. They do most damage between late summer and spring. The easiest way to confirm if vine weevil grubs are the culprits is to take the plant out of its container and inspect the roots. If you find creamy coloured grubs that resemble very plump maggots with tan brown heads and no legs, and each measuring about 1cm in length then you have found vine weevils. They are often curled in to a ‘C’ shape.
Which plants are most prone?
Vine weevils may damage almost anything you try to grow but some of the adults’ firm favourites include camellias, rhododendrons and azaleas, euonymus and hydrangea.
As far as the grub’s feeding is concerned, anything growing in a container is a favourite target. They adore primulas, polyanthus, alpines, sedums, heuchera, begonias, fuchsias, saintpaulia, Streptocarpus, auriculas, strawberries and ferns.
You are most likely to see the adult vine weevils at night, most of them first appearing in about March or April and continuing to plague you until the autumn. They feed intensely for several weeks and then start to lay most of their eggs in the soil or compost around the base of plants between June and August and these are tiny (less than 1mm in diameter) dark brown spheres. If you find much larger tan brown near spherical objects measuring several millimetres across don’t panic, these are not vine weevil eggs but controlled release fertiliser granules which are often incorporated in to the compost of container grown plants.
The vine weevil eggs hatch out in to grubs and having fed well these then pupate in the soil or compost. The pupae look like a cross between a grub and an adult – largely keeping the juvenile features but on close inspection you should be able to see some of the adult features including the legs and antennae beneath the outer ‘skin’.
Vine Weevil control
- If you are lucky enough not to have this pest in your garden you should make every effort to ensure that you keep it out. Buying plants only from reputable sources and checking them over carefully helps. Look out for signs of leaf notching on this or other plants and only buy plants that look completely healthy.
- We are all tempted to re-use compost, but if there is even the tiniest chance that it contains vine weevil grubs, pupae or eggs it is something you should never risk.
- There is a very effective and safe biological control available. The nematodes enter the grubs’ bodies and release bacteria that kill the grubs. It is easy to use, just follow the pack instructions and drench the compost. It works best on plants growing in compost (as opposed to those in open ground) and the compost must be moist. It also works much better in loam-free composts than in the John Innes types.
So how can you get hold of the nematodes? There are two pack sizes available and you’ll not find them in garden centres, as they don’t last well on a shelf! But, you can find out more and order them from my Pippa Greenwood website we’ll then send them out speedily, first class post in an insulated envelope for you to use.