The "number one pest" for hardy nursery stock growers will never be completely eradicated but nurseries need to consider new ways of managing vine weevils, delegates heard at a packed emergency summit last week.
More than 100 growers attending the event at the Thenford estate near Banbury heard industry experts outline how a mix of nematodes, biopesticides, pesticides and vigilance is the best way to control the pest, but 100 per cent eradication is unlikely. Vine weevil causes £40m-plus damage to the horticulture industry each year, as resistance to traditional chemical pesticides increases, pointed out University of Warwick researcher Dr Dave Chandler, who is working on AHDB project CP 158: Application & Management of Biopesticides for Efficacy & Reliability.
Darby Nursery Stock technical manager Alastair Hazell said control is about "detail" and making sure the "weakest link" on the nursery takes as much responsibility for control as everyone else. He rewards staff with £2 for each weevil found. "We had a problem 20 years ago and will have in 20 years' time if we don't learn to manage it. We're never going to totally eradicate it." He said pesticides have not controlled the problem but keeping proper records of controls used and checking a central bank of information would help.
Nursery stock crop consultant John Adlam, who spearheaded the event, said he is getting "call after call saying vine weevil control is not working". He added: "We've no longer got a silver bullet. We have a lot of good effective control programmes but not one that does everything."
Giving a grower's perspective, John Richards, owner of John Richards Nurseries, which grows for garden centres, highlighted the impact of legislation to chemical control that has seen product after product withdrawn from use. He also highlighted the problem of resistance to chemicals and the need for more IRAC codes.
Stressing the need for solutions that will protect plants over the longer term, he explained: "I need three products - a one-season product - and another product with long duration, also another product that releases in 24 months, so we can add them all in together in compost at the start and know all protected."
Ayletts Nurseries plant buyer Marcus Cousins said plant pests and diseases are "coming a lot more to the fore" with more container gardening by customers with small spaces. While he welcomed the container gardening trend, it is bringing with it problems for which "we are running out of solutions", he warned. "When I started there was a shelf of products to help with vine weevil. Now it is gone."
In a presentation that included a review of current available options for vine weevil control and a look at current research, Jude Bennison outlined the findings of a 2014 AHDB-funded MOPS trial into the control of larvae on Fuchsia erecta. She concluded: "For preventive chemical control consider Exemptor. For preventive biocontrol, and in crops in peat-free, consider Met 52 granular if temperatures are suitable. For curative, chemical control consider Calypso drench or nematode products - equally effective."
Dr Colin Mumford of Bayer reminded growers to use insecticides in accordance with the label, never to underdose and to rotate chemical groups. ICL Professional Horticulture technical manager Andrew Wilson echoed the message, emphasising "safe stewardship" and ensuring label restrictions are followed.
Paul Sopp of Fargro warned growers against assuming that they will not have a problem next year just because they do not have a problem right now - 100 vine weevils can turn into a million in two years, he told the audience. He advised monitoring for adults from May onwards on a weekly basis using euonymous as a monitoring tool in the nursery. Meanwhile, growers should monitor for larvae from June onwards until spring.
Cultural controls such as taking old growing media off the nursery should be followed and vulnerable crops placed away from hedgerows and grouped to make monitoring easier. He discussed best use of nematodes, Met 52 mixed into all growing media "from plug to final potting" to ensure best results and chemical sprays for adult control and chemical incorporation for larval control.
To make integrated pest management programmes effective growers need to plan what they are going to do, carry it out and review it, he added. "Record which crops you see problems on and where - vine weevils don't move very far. Look at your year and mark out when you are monitoring, when you are applying larval treatments, when you are monitoring for larvae etc."
Sopp said growers are "going to have to learn to work with a number of tools" to achieve 80-90 per cent reduction in vine weevils. After 25 years of research, he knows that collaboration between bodies such as the Food & Environment Research Agency, ADAS, Forest Research and Swansea University is the best way to move forward.
A panel debate chaired by HW editor Kate Lowe, heard representatives from manufacturers, distributors, retailers and growers outline their view of the most challenging issues in managing vine weevil. Bayer's Mumford said keeping an eye on changing regulations is his biggest concern as products are withdrawn. Neonicotinoids are the "elephant in the room" while thiacloprid and imidacloprid are "chalk and cheese" and it needs emphasising that thiacloprid is safe for bees.
John Richards said "the unknown" is his biggest concern about the pest. ADAS's Bennison said the dearth of research funds is her biggest issue, but the AHDB levy helps with that. Delegate Dr Minshad Ansari of Swansea University spin-out business Bionema told delegates the key to the success using natural biopesticides is in attention to detail. Fungi and other biological alternatives can provide high levels of kill rates but growers need to recognise they are living organisms and have to be treated as such.
Meanwhile, Flowering Plants owner Francis Richardson suggested using a trial quantity of SuperNemos. A major problem needs a full dose to the trial area, otherwise the split application method of two half doses about three weeks apart is effective. To prevent future problems, use the same method but only as a half a dose, twice a year, he added.
-VIDEO - to hear the full discussion, see our video of the Emergency Vine Weevil Summit
- The Emergency Vine Weevil Summit was organised by the HTA, ICL and Bayer with Horticulture Week as media partner. It was also supported by Fargro and BASF.
- See also our fact sheet on the management of vine weevil.