Vine weevil and the evils of ...

Well, I could be accused of being childish with  blog title like that. However, before you start singing 'all creatures great and small to me', I have plenty of experience of loss to justify my abhorrence of vine weevil, otherwise known as Otiorhynchus sulcatus. In actual fact, for these little lady's (and yes, they're all female ...), who was practically unknown here 30 years ago, there is a lot of information published on them. So rather than ranting about my own experiences and wailing about my losses, I've decided to do some research on them, which I've shared with you below. I've covered their life cycle, some information about their adult and larvae forms, and of course, what to do. While most of the information has been quoted from other sites, the pictures of vine weevil, unfortunately, are my own. Enjoy ...  

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

Adult vine weevils cause notch like  leaf damage, which can be unsightly but rarely affects plant growth. The adults are 9mm (about 5/16in) long, dull black beetles with a pear-shaped body when viewed from above. Adult weevils may be seen on the foliage at night; during the day they hide in dark places. They are slow-moving insects that cannot fly but they are excellent crawlers and climbers (https://www.rhs.org.uk). The adults have a long snout and if you spot an them, it is likely to lay still and tuck in it's legs as a form of defence. (http://www.thegardenshop.ie). Adults are mainly nocturnal and only feed at night. Adult vine weevils appear between March and April from the soil of indoor pots, and between May and June from outdoor pots and borders (http://www.bbc.co.uk). 

So, what to do?

Well, there's plenty of really interesting and practical advice for us, from some chemical controls, to using natural predators to good gardening habits to type of soil used. Here's a selection that I've come across divided into prevention and physical controls, biological and chemical control, with a few top tips to finish...

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).

  

Taking it a stage further, in plant growing, the hygiene starts with sterilising pots [I use milton, yup for baby bottles or jeyes fluid] and clean compost. Not doing the basics here, then propagating plants and then handing out to varying punters is what gives some nurseries a bad name, or allows you the individual to fall out with friends and family (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)

Replant perennial pot plants in the spring and look for and remove any vine weevil larvae you find. Quarantine or dispose of any soil from pots where vine weevil have been found. Don't reuse this or throw on the garden because it may still contain vine weevil eggs, larvae or pupae. Remove plants that have unexplainably wilted and died and examine the roots. If they appear eaten, then search the surrounding soil and destroy any vine weevil larvae that you find (http://www.bbc.co.uk).

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/

Adult vine weevils hide in debris around the bases of your plants so try to keep the area immediately under them free of dead, fallen leaves and reducing the number of places that they can hide. As the adult vine weevil will lay its eggs in the soil at the base of its preferred plants you can consider using physical barriers such as landscape fabric or Mypex to prevent the newly hatched larvae from entering the soil. This is a simple yet effective method that will deter the adults from laying eggs preventing further insect damage (https://gardenofeaden.blogspot.ie)

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).

Use commercially available nematodes (microscopic worm-like creatures) Steinernema kraussei and Heterorhabditis megidis that can be watered into pots or surrounding soil, during the summer months, to control vine weevil larvae. The nematodes seek out and kill vine weevils (http://www.bbc.co.uk). Either can be applied to the soil in late Summer. But their effectiveness is limited by their ability to survive cold conditions and dry or heavy soils (http://www.thegardenshop.ie). Surprisingly it is not the nematodes that kills the larvae directly but a particular strain of bacteria that they carry which will infect the vine weevil larvae, killing it. The nematodes then invade the body to feed on the contents and breed (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)

Adult weevil damage is difficult to prevent but you can protect plants against the larvae in late summer by applying a compost drench to ornamental plants grown in pots, such as Provado Ultimate Vine Weevil Killer 2 or Scotts Bug Clear Vine Weevil Killer (http://www.telegraph.co.uk). Note: It is important to read manufacturer's instructions for use and the associated safety data information before applying chemical treatments (http://www.bbc.co.uk).

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/