Vine weevil are still considered the nursery sector’s number one threat, and continue to account for the highest level of RHS pest control enquiries from gardeners. It regularly gets mentioned on Gardeners Question Time and in the gardening press. For commercial growers, ensuring early protection of the roots is key to maintaining a vine weevil free status in containerised plants, according to experts.
Neil Alcock is the chairman of the ALP (Association of Liner Producers) and nursery manager of Seiont Nurseries in Gwynedd, North Wales. Producing 900,000 P9 pot liners and 400,000 4cm plugs per year, the nursery spans 30 acres, with 18 acres under protection, and they specialise in new introductions, stocking a wide variety of shrubs, ferns, grasses, and herbaceous plants. They take their own cuttings and have two contract micropropagation units.
Dangerous pest
“Vine weevil live naturally in the hedgerows surrounding the nursery,” says Alcock. While they don’t fly, the pests are mobile and will readily walk in, feeding on plant leaves as adults, laying their eggs in the compost and producing larvae that eat away the plant root system. This stage can be the most dangerous in the lifecycle, leading to an often sudden collapse of the plant.
Recognising the dangers presented by the pest, the ALP stipulates that liners are grown in vine weevil treated compost, protecting the plant from the core. “If we didn’t do this, there is a chance of vine weevil infestation, if not on our nursery, at our customers,” he explains. By treating the compost around the central roots, customers know that when they pot on using treated compost, they are adding a further defensive barrier rather than defending an unprotected core. “This also gives ALP members a competitive advantage over imported stock that is largely untreated for vine weevil.”
Seiont specifies the use of Vi-Nil for treating compost. Alcock is of the view that no other product will deliver 100 percent control. “We have used two other main competitor treatments and found that vulnerable plant types such as hardy ferns and heucheras would fall victim to the pest,” he claims.
Imported plants
Alan Horgan, technical officer for Certis who market Vi-Nil, says that while nursery stock that is treated from the very earliest stages of production is the ideal, a lot of imported plants arrive here untreated, heightening the importance of effective quality control measures on arrival. “We are still the only country in Europe with registration for Vi-Nil, the UK’s market leading product,” he says.
“Procedures to protect yourself and your stock are ensuring you buy from a reliable supplier - check them out and subsequently check stock on delivery. Quarantine it if you have the capacity and be particularly wary of plant types favoured by vine weevil, such as eleagnus, heuchera and primula species. You can then treat the root balls of plants if necessary using a nematode drench treatment.”
For growers potting-on using Vi-Nil, Horgan explains that the treatment has a migration effect that is useful to protect an untreated root ball. The granules release slowly over at least a two year period and always seek to find an equilibrium in the compost. “So, an area of high concentration will move to an area of lower concentration until a balance is achieved, providing an even distribution and level of control through the compost,” he explains. Nonetheless, there is a time delay to see the full effects of this process, so the earlier a plant receives treatment, the better the overall protection.
Certis anticipates Annex 1 listing shortly and that will pave the way for European registrations of Vi-Nil in Holland and other countries through the process of mutual recognition.
Vine weevil life cycle
The adult vine weevil emerges from the soil between April and June. After six to 10 days it starts actively feeding at night on the foliage of plants and then the adult female is capable of laying viable eggs just two weeks later. Several hundred eggs are deposited in the soil, often near to the host plant, from July onwards.
The high moisture and humidity levels often found in nurseries favour egg survival and larvae hatch from the eggs two to three weeks later and then start feeding on the roots, corms or rhizomes of the host plant. Feeding continues over a prolonged period of several months, which includes a period of overwintering in the soil.
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