Vine weevil control

by Kate Bradbury

Last week I found vine weevils on the rim of my the pot my orange tree lives in. It stands next to my 'nursery' of seedlings, so potentially hundreds of plants could be affected.

Vine weevil adult on leafLast week I found vine weevils on the rim of the pot my orange tree lives in. It stands next to my 'nursery' of seedlings, so potentially hundreds of plants could be affected. The adults cause little damage, save for a few nibbles on the edges of leaves. But their larvae can kill plants by eating their roots.

The adults will lay eggs anywhere, but prefer an open soil in which the larvae can move around freely. A light, peat-based compost is ideal for them. I don't use peat, so I consider this invasion to be extremely unfair.

So what to do? 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.

I spoke to David Morris from Bayer, which makes Provado Vine Weevil Killer 2. He said there was no evidence to suggest that thiacloprid killed bees. But I choose not to use pesticides in my small garden, so have opted for alternatives.

Vine weevil larvaeIn future, I'll empty out all my pots and inspect them for grubs each spring. But this time I'm using nematodes. These are harmless to wildlife, but attack and kill vine weevil larvae within three weeks. I've heard mixed reports about nematodes - some people claim they don't work - so I'll repot my orange tree next month to be on the safe side.

I've been leaving my girlfriend gardening tasks to do while I work: transplant the zinnia, sow more basil, repot the strawberries etc. She proudly showed me the little pots of zinnia one evening. "Did you find any little white grubs in the compost"? I frantically asked. "No". Phew! "But there was one in the strawberries. It was cute and wriggly. And an earwig".

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Gardeners' World Web User 24/04/2010 at 09:00

Kate - when you repot your orange add a thick layer of gravel over the compost. The vine weevils won't be able to lay their eggs. Thanks for the pesticide info. Dot

Gardeners' World Web User 24/04/2010 at 12:17

I found out years ago that any trouble from vine weevil came into my garden from nursery or gift plants from friends so now all are washed of their compost and transferred to scrupulously clean pots with new compost - cheaper in the end than taking short-cuts. The old compost is consigned to the compost heap which earths up potatoes when done. So far I have not had to buy nematodes. Good husbandry usually pays well so, as rain is forecast through the night, I shall be up early tomorrow morning looking for slugs to remove from my sugar-peas, lettuce etc.

Gardeners' World Web User 25/04/2010 at 09:34

I've just found my first lavae in my old strawberry pot (yesterday)....I painstakingly went through all the old compost removing the grubs and then thoroughly cleaned my pot (replenishing with new compost) - can I assume that as the grubs were in one of my pots - all others nearby will also be affected?

Gardeners' World Web User 25/04/2010 at 21:14

After a root washing seesion this last week I now have all my pots standing on pot feet in saucers which i will have to keep topped up with water - I've heard this can prevent vine weevils. Lost a couple of plants esp strawberries to them last year!

Gardeners' World Web User 26/04/2010 at 08:40

Thanks for the tip Dorothy. I agree with happymarion - good husbandry is indeed the key. I spent the weekend uncovering vine weevil grubs - which I put out for the birds - and squishing hundreds of eggs. Lovejoy I'm afraid all your pots are probably affected. Kate

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