The first sign of black vine weevils, Otiorhynchus sulcatus, is usually when one of your favourite pot plant wilts and dies in the spring. The larvae, small creamy white sickle-shaped grubs, devour plant roots and then the base of the stems until the plant keels over. The grubs are a major pest in nurseries where there are many plants in containers. Out in gardens they attack many varieties of ornamentals including rhododendrons and camellias plus crops such as strawberries. Although outdoor attacks are seldom fatal they weaken the plants.
When adult beetles emerge in April they are only 10mm long and nocturnal. The adults cannot fly but can run fast and climb plants at night, feeding by taking bites out of leaves. By day they hide under any debris on the soil surface to avoid being eaten by predators which include birds, frogs, toads, shrews, hedgehogs and other beetles. In the autumn they lay eggs in the soil, the larvae then munching away unseen all winter.
In a refreshing change from previous advice on controlling infestations, gardeners are advised against pesticides that will kill the predators of the beetles as well as their prey. Instead gardeners are advised to hunt down weevils with torches or buy biological parasite controls that eat the larvae.
Comments (…)
Sign in or create your Guardian account to join the discussion