White grubs in potted plants

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LakeView
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White grubs in potted plants

Postby LakeView » Mon Feb 20, 2006 11:22 pm

Hi,
I too have recently found white critters -- but they are destructive white grubs in the soil. They've been decimating the roots on my (ok it's not veg!) polyanthus plants. I found them in pots that I transplanted last autumn -- and in the severe cases they had eaten the entire root system, leaving the greenery on top. The plants have been outside all winter, on shelving, not in cold frame or GH or tunnel. In some cases there were at least 2 dozen in one 8" shallow pot.

What are these, please? I've never come across them before.
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Postby Chantal » Mon Feb 20, 2006 11:26 pm

Sounds like Vine Weevil to me but I'm not sure what you do about it. I do know you have to squash all the grubs and wash the roots of the plants, if there's anything left to wash. Don't know any more I'm afraid. :(
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LakeView
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Postby LakeView » Mon Feb 20, 2006 11:32 pm

Thanks. What do they grow up to be? Are they fliers? Almost all these plants were on the top shelf at chest height. I've never seen them before. And, yes, I did a lot of squishing. Didn't wash off roots, though. Will have to keep an eye on them for a while.
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Postby Chantal » Mon Feb 20, 2006 11:38 pm

I've just remembered I read an article on these little suckers in a past copy of KG (Jan 01). This is what is says:

"Description: The adult weevils are flightless beetles whose hardened forewings, or elytra, are sealed to form a protective shield over the abdomen. They are nocturnal, feeding on leaves by taking characteristic bites out of the leaf margin. Emerging in April, they are usually present until October (although they can be found all the year round under glass), during which time many hundreds of eggs are laid on the soil adjacent to suitable host plants. The eggs hatch into white legless grubs with distinct brown heads. The grubs start feeding on the roots. Feeding continues as the grub growns to about 10mm, before burrowing deeper into the soil for pupation. Development from egg to adult takes between nine and eighteen months.

Damage Caused: Adult feeding is seldom a serious problem, but the grubs can seriously damage roots, especially in container-grown plants, causing wilting and eventual death.

Plants Affected: Most ornamentals and any other plants grown in containers or in sandy free draining soils. vine weevils are prone to drowning in wet conditions in clay soils.

Control: The preferred option is the use of parasitic nematodes Heterorhabditis (available from Defenders 01233 813121), that are specific to vine weevils. These are applied to the soil in September, and usually again in April to achieve very satisfactory control. The broad spectrum insecticide imadocloprin is readily available for vine weevil control (warning: not approved for use on food crops), but if you care for your ground beetles, stick to your nematodes."

Hope this helps. :)
Chantal

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Postby Jude » Mon Feb 20, 2006 11:40 pm

Definitely vine weevil I'd say, and I've had plenty of experience of the little b...ers. You can buy nematodes apparently which you water in when potting new plants, but I've not been able to afford it. Afraid that you will need to chuck out everything affected completely, compost and all. Don't put any of it on your compost heap or on the garden. Wash out pots and start again. I have found that a gravel mulch works well to stop the weevils getting in and laying their eggs in the first place.
Must admit I was reduced to tears when I lost a beautiful and expensive acer to the dreaded grubs.
One is also supposed to go out at night with a torch and pick the adult weevils off the leaves of plants....yeah, right!
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Postby Chantal » Mon Feb 20, 2006 11:46 pm

I found them on a miniature conifer I had in a pot. The roots were almost gone but I tipped all the compost into a carrier bag and binned it then washed the plant, washed the pot and replanted. That was about 10 years ago and it's going strong. Maybe I was just lucky but no-one told me not to so I just did what I thought was the right thing and it worked.
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LakeView
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Vine Weevils

Postby LakeView » Mon Feb 20, 2006 11:47 pm

Many thanks for the explanation and detail - both of you.
Anonymous

Vine Weevil Grubs

Postby Anonymous » Tue Feb 21, 2006 10:13 am

Don't throw away the vine weevil grubs. Collect them in a shallow container, and put them out for the birds. They love 'em, and its a bit of fresh protein for them when other insects are scarce!

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Postby peat » Tue Feb 21, 2006 11:33 am

All vine weevils are female. They love soiless composts and polyanthus. In college we always washed the roots when we found any in pots that had enough roots to be able to save them.
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Postby Tigger » Tue Feb 21, 2006 1:34 pm

The dreaded vine weevil - as well as the nematodes, there's a powder solution available at garden centres that you mix up and water in. I've had some success with that, but it's not cheap.

They don't seem to cause much trouble in open ground, but they'll decimate anything in a pot.

M.
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John
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Postby John » Tue Feb 21, 2006 3:24 pm

Hello Lakeview
The vine weevil problem is well-covered on the RHS site:

http://www.rhs.org.uk/advice/profiles06 ... weevil.asp

with some good photos as well. If you are going for a chemical treatment, the stuff you need is Bio Provado Vine Weevil Killer. I've used it on pots with fuschias in and it has been very effective. The problem seems to be worse in pots filled with peat or similar potting composts. The grubs feed on the roots and will soon destroy a plant from below. The first sign of trouble is usually unexplained wilting of the top growth because of the root damage. I don't think you can use it on edible crops - you will have to use the nematodes then.

John
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LakeView
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Postby LakeView » Tue Feb 21, 2006 7:57 pm

Now I'm all depressed! :cry: Well, at least I know what it is now and can attack the problem right away.

Thanks for all your help. The RHS site has a photo of my grubs. :cry: :(
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Postby john english » Wed Feb 22, 2006 9:56 am

I feed any I find to our goldfish in the pond they love them
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Postby Di » Wed Apr 05, 2006 10:24 pm

Just to add, the adult vine weevils play dead when threatened - so don't be fooled, stomp 'em anyway.
Shelley

VW Grubs

Postby Shelley » Sun Apr 16, 2006 10:56 pm

Boy is THIS a hot topic right now, and not having 'forummed' for a while, I was going to post this up, but no need now !!

Today, Trousers and Me (well, Trousers actually) dismantled the terracotta Strawb Pot. For 'obvious' reasons really, which would be why I'm posting this.....

GUESS HOW MANY ? Grubs, that is.
No. I kid you not - 254.

My question to The Forum was going to be, shall I put them on my bird table.

Now that I know the answer, I'll get my coat...

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