In his new book, Down to Earth, published by Dorling Kindersley this October, Gardener’s World presenter Monty Don says garden centres are the cause of one of the fastest growing problems in the garden – the vine weevil.
Nursery experts agree that vine weevils are now considered to be the most serious pest of ornamental plant production. The black vine weevil (Otiorhynchus sulcatus) and other closely related weevil adults feed on susceptible plant foliage leaving notched edges, while it’s the larvae feeding extensively on plant roots that do the most damage. Vine weevil grubs are responsible for killing plants such as potted heucheras, primroses and soft fruit bushes. It is estimated that vine weevil damage causes a staggering £30m in annual losses for growers and that total is expected to increase with the restriction of potentially bee-harming, neonicotinoid-based, pesticide control options.
Monty said: “Vine weevils are often introduced to gardens via plants bought in containers at garden centres. It is worth lifting any plant before buying, and checking the roots to make sure no vine weevils are there.”
He added: “They are second only to slugs and snails as a horticulture hate figure, particularly to plants in containers, yet I confess that I have never had to deal with any of them.”
Buckingham Nurseries’ Chris Day says Monty’s statement is rather “sweeping” and “broad brush”, though he admits, vine weevils are an increasing problem. He said commercial growers are doing their best to keep the problem down. Chris said gardeners manage rather than really control vine weevil and said checking plants in the nursery was not a bad idea.
Some horticulture experts say vine weevils live in the wild and are more likely to get into garden plant pots from the garden than from shop-bought plants. Chris said because one adult can lay up to 60 eggs, having just one in the garden “to rock the boat” can cause havoc.
One way for home gardeners to tackle the problem is with a new range of nematode treatments for tackling leatherjackets, chafer grubs and vine weevils from naturals control brand Neudorff that do not require refrigeration and have a shelf life of six months. Previously, gardeners usually bought nematodes by mail order because they have a limited life so can’t be stocked in stores.
The new product works through Cryptobiosis, a metabolic state of life entered by an organism. The nematodes are suspended in a formula that keeps them in a suspended non-moving state and maintains the correct moisture level for survival. The encapsulated nematodes are protected from bacterial contamination.
Conventional nematodes, available from the likes of Nemaslug, need refrigeration to slow down their movement and consequently need to be used within a short time frame.
Withdrawn from sale
Controls such as Provado Vine Weevil Killer 2 (containing the neonicotinoid thiacloprid, a neonicotinoid suspected of harming bees) have been withdrawn from sale, as have other products that contain thiacloprid. BugClear Ultra Vine Weevil Killer that contains acetamiprid (also a neonicotinoid, but still available) can still be used as a soil drench for ornamental plants in containers, but not on plants growing in the open ground.