Gardens are looking lovely – new growth and blossom and every shade of green. And happy gardeners listening to BBC Radio 4 Gardeners’ Question Time on 7th May 2017 will have frozen with horror at the description of slugs munching their way through more plants than many gardeners could imagine. The RHS 'top pests' list is enough to frighten me more, but of course it's filled with helpful advice too.
And with horror and help in mind, our garden tips today are all about getting rid of vine weevils before the grubs can kill your cherished container plants this autumn. The grubs form from eggs laid by adult weevils in May/June (depending on your local climate) and while they attack all sorts of plant, they are most damaging to plants in containers. Remove the adults before they lay eggs and you can prevent the problem of grubs. And now is the time to act to prevent damage and death.
Vine weevils: identify them
Adult vine weevils (Otiorhynchus sulcatus) are about 9mm (5/16in) long and a dull black colour with grubby off-yellow marks on the wings. The leaves they eat will have irregular notches on the edges in summer. The small white grubs are the most common cause of death in container plants, and are most active in the autumn.
Vine weevils: hands on now and get rid of them
- On mild evenings take a torch and large newspaper or old sheeting onto your patio. Use the torch to take a good look at the plants in your containers, the walls or fences near them, the saucers under them and any structures supporting them.
- If you can, lift up containers with shrubs and shake them over your old newspaper or sheeting to dislodge the weevils.
- Wear rubber gloves and squash the weevils.
- In greenhouses, use sticky barriers to trap weevils on the edges of pots or on the edges of benches or staging. greenhouse staging
- Encourage natural predators. Vine weevils (and their grubs) are eaten by birds, frogs, toads, shrews, hedgehogs and some beetles.
Vine weevils: bring in biological controls
Nematodes (Steinernema kraussei) that kill the grubs are best used in August or early September. At this time of year one variety of nematode (Steinernema carpocapsae) can be used to control adult vine weevil. Traps containing these nematodes are placed on the ground below plants that are likely to be damaged by the adult weevils from now on. The adults go into the trap during the day and are infected by the nematodes.
The last resort: chemical control of the grubs of vine weevils
In late summer the last resort treatment to kill grubs is to use a commercial insecticide (such as ‘Bug Clear’ or ‘Vine Weevil Killer’) in water on the soil in the containers of ornamental plants. The ingredients in such mixes is contentious, including neonicotinoids about which many gardeners are very concerned because of its effects on bees and other wildlife. Much better for the world is a quiet evening squashing the adults.
Good luck for healthy and long lived container plants!
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