Friday, October 05, 2012

Banish the Evil Weevil

It's that time of the year again, when I have to do a particular autumn ritual that I don't necessarily enjoy but I know I have to, for if not we will suffer the consequences later on. And it's something to do with a specific pest control.

Echeverias - gourmet and preferred food of choice for vine weevils. Echeveria agavoides
Adult Vine Weevil (photo from the RHS website)
Mostly because I regard it as boring and tedious, for it involves watering every single potted plant that we have (and we have hundreds!) as well as drenching the ground of virtually the entire garden with a prepared solution. But it's all for good.

Think of the plants, think of the welfare of the plants, I tell myself. They need protecting from a particularly nasty bug that attacks, benignly from the outside as adults but as larvaes, fatally from the inside, within the soil, feeding on the root system of an afflicted plant. I am of course referring to the dreaded Vine Weevil.

Vine Weevil larva
Many gardeners dread this garden pest, me included. For the first couple of years since we started gardening here I didn't spot any signs that this nasty bug was present in our garden. So far so good. Then later I spotted some characteristic notches on leaf margins of some of the plants. Suspecting that they are the dreaded vine weevil, I went out one evening (adults are nocturnal feeders) and there they were, adults munching away on certain plants. And if there are adults already, they are bound to lay eggs. And when the eggs hatch that's when the real problem starts.

Vine weevil killer nematodes needs to be dispersed in water first.
It was inevitable that we'll get this nasty pest in our garden. For one thing, we buy a lot of plants from different nurseries so it was a ticking time bomb, just a matter of time when we'll inadvertently introduce this nasty pest to our garden. Not to mention getting a cross infection from one of the gardens next to ours. I was sort of expecting it but was hoping it would never happen. But it did so we have to take measures to control this nuisance, to prevent the larvae from killing precious plants.

But Twinkles had decided to help by taste testing the water first!
This pest is not so much of a problem if most of your plants are planted out on the open ground. It's more of a problem for potted specimens. With the larvae trapped within the confines of a vessel (i.e. pot), the entire batch of grubs concentrates all its root eating efforts to what is available within that vessel. And the root system of that potted plant is decimated and consequently the plant dies.

It has a limited shelf life so use as soon as you can.
Scoop from the packet using a garden teaspoon (no, I don't use this teaspoon in the kitchen...)
Disperse, mix, and voila! Ready for use!
So the very thought of precious plants dying is enough to kick start me to action, despite that yes, I still find the deed boring. But it has to be done!

There are manual ways of controlling this pest (no need for me to list them here, it's all out there on www!) but my preferred way of keeping them at bay are via the ground and roots. Kill the grubs and you will control the adults that will continue the cycle. There are two ways of doing this: drenching using a systemic insecticide, and drenching using parasitic nematodes that attacks and kills the vine weevil larvae.

For indoor and permanent greenhouse plants, I use the former. For outdoor potted plants and drenching the ground I use the latter. Using nematodes is the most cost effective method when used on bigger areas and having high volumes of potted plants. And it's organic; it specifically targets vine weevil larvae and is harmless to virtually everything else (humans, pets, aquatic life, and other insects).

The only disadvantages to using nematodes are it is season, weather, and temperature dependent. It is best applied in the spring then again in the autumn when ground temperatures are still above 5 Celsius. And as it uses moisture to swim towards its target (vine weevil larvae), it is best applied on a rainy day.

Tell tale signs that adults are present in the garden...
This Daphniphyllum pentandrum is a perennial favourite of them!
And today being a typically rainy autumn day, it was the perfect time to give the garden and plants its autumn dose of vine weevil killing nematodes. Which also made me smile for yes, I have just been watering outside whilst it was raining!

And one other thing, as nematodes are living organisms themselves they have a limited storage life span. Buy them around the time you actually need them and use them as soon as you possibly can after you buy them (or arrives to your door if bought via mail order).

Bergenias, another favourite of theirs!
So how do you use it? Just follow the instructions on the packet, it's difficult to get it wrong. As for me, I've used this so many times that I have developed my own technique to using it.

So far so good, I have yet to find grubs in the garden whenever I do spot checks of potted plants and their rootballs (or post mortem if a plant has died for some reason). But we always get the adults, albeit seemingly diminishing in numbers every year.

So if I drench twice a year, every year, how come we still get the adults? Where are they coming from?

Funny enough, I found the answer whilst inside the big pond. Whilst using the vacuum cleaner on the dry pond floor one morning, I found a few vine weevil adults crawling on the pond wall and coping stones, they were heading towards the neighbours garden. This was in the morning, which meant in the evening they head towards ours to eat, then back again to the neighbours to sleep.

Sometimes you get answers to life's questions whilst using the vacuum cleaner...
But they could lay their eggs virtually anywhere so it's still worth protecting what we have within our garden boundaries. I may not have control of our neighbours but I have control of ours.

Vine Weevils absolutely adores Echeverias. I've found several adult vine weevils going in and out of pots with Echeverias on it hence all potted ones are thoroughly drenched and regularly checked.
It just means I have to do this routine twice a year, year in and year out. Boring but necessary. Never mind, it's all for the well-being of our plants!



  1. Hmm I think that is what I just stepped on out back. I guess I need to check the gardens more thoroughly. Going back out now to check. Thanks for the information.
    Cher Sunray Gardens

    1. Hi Cher, I don't think all weevils are garden pests. So worth checking what they look like. Vine weevils are pretty distinct which makes them easier to differentiate from the others.

  2. We have grubs in our soil that look very similar to your grubs, they are such a nuisance, and i have also found some on the odd occasion in pots. I think our grubs are related to a beetle, nonetheless they still eat plant roots, whenever i see them, they get squished.

    1. Hi Karen, a few grubs found on the soil is not always a cause for worry. There are natural predators the usually keeps the numbers down when found on open ground. It's more of a problem for potted plants.

  3. ARG! Weevils have become the bane of my existence! For years, and through several gardens, I didn't even know that they existed. Finally, four years ago signs of their dining on my plants began appearing. I like to garden organically and when a pest arrives I usually do nothing, thinking that healthy plants can take a little chewing and that there will be a natural balance of some sort. Not the best attitude to take with these leaf thirsty fiends! They seem to love my garden and have spread about, setting up new little communities all over the place. I've been spraying beneficial nematodes spring and fall for the last 3 years and they still seem to be growing in number. I'm seriously considering using a chemical remedy but am afraid of the effect that might have on all of the beneficial soil dwelling organisms. What to do, what to do...

    1. Hi Outlawgardener, if the adults live and breed on the soil/pots from a different property then there's not much you can do about that, however you need to carry on protecting from within your garden. I do use systemic chemicals on houseplants/greenhouse but probably best to avoid using that on open ground, nematodes are much better and safer for that.

  4. Can I dare say that we don't have them? No! I'm sure we do but fortunately not in abundance, but after reading this I will check! Thanks very informative x

    1. Hi Libby, you could be lucky and not have any. Some gardens seems not to have any vine weevil problems at all :) Continue keeping an eye though, just in case.

  5. I've never seen these bugs, though I've seen lots of holes which I have always blamed on slugs so far. I shall now add weevils to the list of suspects!

    1. Hi b-a-g, if the leaves have got as much holes in the middle as notches on the leaf margins, more likely it's caused by slugs and snails. Vine weevils tend to nibble on leaf margins only, causing the tell tale signs of notches on the leaves.

  6. Good shots .....i like the headphoto of this blog also very much.

    Greetings, Joop

  7. Not a nice subject - or chore - but some lovely plants that you are protecting. ?! As to running the vacuum round the pond, nice try, sneaking that in, but good grief, why?!

  8. Excellent post.Thanks for you post.

  9. Having just created what I call a living lid using sempervivums and sedum - I'll have to look out for these pests. I didn't realise they were a problem for these plants having few roots.

    1. Sorry it was an echeveria wasn't it - quick glance and not reading closely enough - do you find them a problem with sempervivums?


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