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Vine weevil is an insect that can infest a wide range of ornamental plants and fruits, especially those grown in containers. Adult vine weevils eat leaves, and the grubs eat roots (https://www.rhs.org.uk)
The life cycle
Vine weevils are parthenogenetic (only females, reproduction without males) and only reproduce once a year. Many adult weevils emerge in late spring and early summer, when a feeding frenzy commences before of egg-laying. Some adults emerging later in the year can survive overwinter given favourable conditions. Eggs laid on the plant or soil surface hatch after several days and the larvae burrow into the soil where they can feed on plant roots. After several developmental moults, the majority of weevils overwinter as larvae before pupating at the start of spring. (http://www.fruitdisease.co.uk)
The grubs
Typical vine weevil grubs are creamy-white, up to 13mm (0.5in) long, C-shaped, with a brown head and no legs and will eat the roots of a wide range of different plants. (http://www.gardenforumhorticulture.co.uk) including roots, tubers, corms and the lower stems of susceptible plants (http://www.bbc.co.uk). In the past, their favourite food was fuchsias, cyclamen, begonias and primulas. But in recent years they have become less fussy and will make a meal of a much wider range of plants - especially any that are growing in containers. This is possibly due to the use of peat-based and peat-free composts - being less gritty than John Innes composts, the adults are more likely to lay their eggs in them (http://www.gardenforumhorticulture.co.uk).
The adults
So, what to do?
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Prevention and physical controls
Garden hygiene in short is all about keeping your garden tidy, regularly. In that I mean really really giving it a good decent once over down on your hands and knees 2- 3 times per year. And it is the not doing that that encourages the Vine Weevil’s to set up home in your patch or garden (http://doneganlandscaping.com).
In choosing plants, I only choose my plants from good nurseries. And a quick survey of their plants, should it be necessary will tell me if they are using products like Suscon Green of old or Supernemos to prevent the Otiorhynchus sulcatus from developing further, prior to being brought into your garden (http://doneganlandscaping.com).
As feeding generally occurs during the night, weevils can be controlled by nocturnal gardening! Go out with a torch and spot and remove beetles from infested plants. Use an upturned umbrella positioned underneath your plants to catch weevils as you knock them off (http://www.thegardenshop.ie).
Vine weevil changing into an adult |
You can set up a Vine Weevil trap. One example is to use corrugated cardboard, rolled up into a tube and held together using an elastic band. Position this inside infected plants at night and the next morning you should find several Weevils inside (http://www.thegardenshop.ie)
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Physical barriers on top of the soil or compost also work very well. Add a 2cm (0.75in) deep layer of sharp grit or gritty gravel on top of the compost or around the base of the plant to prevent the adults from laying eggs; the egg-laying structure is irritated by the scratchy feel (http://www.gardenforumhorticulture.co.uk).
Another way is to use a physical barrier as the adult beetles cannot fly from plant to plant. Stand potted plants on upturned pots sat in saucers of water - the adults can't swim. Or surround the pots with Barrier Glue available from Agralan - the adults cannot walk across it. With either of these methods it is important to move plants away from walls or greenhouse/conservatory walls as the adults can jump down onto them; they cannot fly. http://www.gardenforumhorticulture.co.uk/
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Biological Control
We are lucky in this country as there are a number of native predators that will make short work of both adult and larval vine weevils, it is just a matter of encouraging them into your garden. The easiest way is to provide a wildlife pond and or log piles. This will attract a number of very useful mammals, amphibians and predatory insects into the garden which will feed on vine weevils, but it doesn't stop there as they will also devour other garden pests such as slugs and snails (https://gardenofeaden.blogspot.ie).
Chemical Control
Avoid using broad spectrum insecticides which will kill soil-dwelling predators of vine weevil larvae, such as centipedes and carab beetles (http://www.bbc.co.uk)
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Pesticides applied every spring and autumn will kill the larvae. But I worry that the active ingredient (thiacloprid - a nicotinoid compound related to imidacloprid) also kills bees and other wildlife (you can read more on the subject here). The theory is that the thiacloprid is absorbed via the roots into the plant's sap, pollen and nectar, and that anything that feeds from it can die. Thiacloprid is active for up to three months and imidacloprid can last for up to six months (http://www.gardenersworld.com).
Top tips from a recent Twitter conversation started with greensideup.ie
@Greensideupveg, to add to the existing body of information above, I hope this short selection of tweets does the long and very good conversation justice:
Seems to have been a bad year for them [vine weevil], I'd clear out sterilise the pots, use John Innes Compost and repot Lord WishWellingtons@Helmsleygardens
They can't swim though. Drown them. If its cold they need longer Charlotte Moss@cmossperennials
A good tip, if it's a plant worth saving is submerging the plant/pot in water overnight. TallGardenerEoin@eoin_mcguigan
[On drowning vine weevil] Try the tiniest drop of detergent, to break surface tension. They'll mostly drown before plants Charlotte Moss@cmossperennials
[On using nematodes] Nematodes are non native. I find more concrete result with topdressing (examining visually) Charlotte Moss@cmossperennials
Yes, repotting pref twice yearly for vulnerable plants, mulch with grit...Harriet Rycroft@HarrietRycroft
When I buy primulas/Heuchera/succulents I wash all compost off. Harriet Rycroft@HarrietRycroft
When I repot, I put all the old compost in the chicken run,they love weevils! Lynn O'Keeffe-Lascar@OkeeffeLynn
Some final words from Geoff Hamiliton's 'The Organic Garden Book' (Dorling Kindersley, 1987):
Start by growing strong, healthy plants that have the ability to resist attacks from pests and diseases. Always plant into fertile soil and make sure the plants never go short of water and food. rely as much as you can on physical methods of pests and disease prevention and control and constant vigilance ... and nature will do the rest for you'.
Please leave your comments on this topic below,
Happy gardening
Information has been drawn from the following website links today, the 30th of November 2016. Please feel free to cut and paste these links into your browser to visit for further information and insights:
https://www.rhs.org.uk/advice/profile?PID=234
http://www.garden.ie/gardeningtroubles.aspx?id=651
http://www.fruitdisease.co.uk/EntomologyResearchPage3.asp
http://www.thegardenshop.ie/control-vine-weevil/
http://www.bbc.co.uk/gardening/advice/pests_and_diseases/identifier.shtml?black_vine_weevil
http://www.nickykylegardening.com/index.php/blog/352-the-fruit-garden-and-orchard-in-may-2015
http://www.gardenforumhorticulture.co.uk/pestwatch/vine-weevil.htm
http://www.telegraph.co.uk/gardening/gardeningpicturegalleries/9113329/Garden-pests-to-look-out-for-in-pictures.html
http://doneganlandscaping.com/blog/2013/06/07/vine-weevil/
https://www.theguardian.com/lifeandstyle/2009/sep/12/vine-weevils
http://www.gardenersworld.com/blogs/gardeners-musings/vine-weevil-control/2968.html
https://gardenofeaden.blogspot.ie/
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