Dug up one and it just looked thin and ragged. Assume it is vine weevils, so have soaked the compost with an insecticide, although given the amount of rain we have had I think it might have been well diluted by now. Wanted to do something for over winter, but will certainly use nematodes next year to see if that helps.
Thanks for your help everyone,
Thanks for the message but I'll reply here so people can correct me if I'm wrong. I don't have much experience with pesticides but as far as I know you can only treat vine weevils in pots effectively with the right pesticide so if yours are in open ground then it might not be as effective. I looked into this because it seemed like pesticides used in the right conditions might be more environmentally friendly than releasing nematodes. I'm not convinced either way though at the moment. http://https//www.rhs.org.uk/advice/profile?pid=234
Assuming you used the correct vine weevil neonicotinoid then it should be effective in the plants for about 4 months, but that is the given period for pots so I don't know how well it will work in open ground. Neonics have been shown to affect aquatic life in the run off from gardens and fields so it's very probably that it would also kill nematodes in the residual period. Given the cost of nematodes if nothing else I wouldn't risk it.
The recommended pesticide is Acetamiprid (same stuff used in pet flea treatments) https://en.wikipedia.org/wiki/Acetamiprid which is systemic and will be taken up by the plants rather than just treating the soil. Removing flowers will protect pollinators but it's probably unlikely to last until flowering now.
Given you haven't found any vine weevil grubs yet though it might be worth being cautious before treating just in case. I've never lost plants to grubs in open ground despite having quite a heavy infestation here. I don't grow hostas though so it might be a different case with you. The systemic pesticide should protect the plants for now though anyway.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
Thank you for all this information, really helpful. I am not sure what the pesticide is that was in the one I used, it was 'BugClear™ Ultra Vine Weevil Killer' which it said, is a systemic and contact insecticide for the control of Vine Weevil in pots and hanging baskets. This product works in roots and in the soil to protect the whole plant for 2 months. Kills whiteflies, blackflies, scale insects and mealy bugs.
So as it only lasts two months, I am guessing it will no longer be effective by the spring, and may not be a risk to pollinators. However, as I do not think that flowers on hostas are that striking, I will remove them next year to be on the safe side.
Would it be better to wait and see what the hostas are like next year? That have all been cut back now and will start to show in late spring. If the new shoots are weak would that be too late to try nematodes? I have used them previously for slug control, using them during the summer for two consecutive years, and they worked well.
I do try as much as possible to avoid using insecticides and most of the time it works, but I really am a novice at it.
Thanks again to you and DovefromAbove for all your help and advice.
Well (assuming it is vine weevil since we don't actually know yet) any grubs that try and munch the roots for the next 2 months should be killed by the insecticide. You may get more hatching in the spring after the effects wear off so that would be the time to apply nematodes again when the soil warms up.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
The nematode suppliers tell you not to use insecticide as well but given the time lag I think you should be ok. Maybe your Hostas just needed dividing & some fresh soil / compost. If they have been in the same place for some time they will have used up a lot of nutrients.
Again thank you for your advice and help. I do feed them regularly and they have had a mulch most years of leaf mould or compost. But they have not been divided since being planted about 5/6 years ago, so will look at doing that next spring. Will also use. Nematodes next year. Don't want to lose them. All your help is so welcome and appreciated.
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Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
So as it only lasts two months, I am guessing it will no longer be effective by the spring, and may not be a risk to pollinators. However, as I do not think that flowers on hostas are that striking, I will remove them next year to be on the safe side.
Would it be better to wait and see what the hostas are like next year? That have all been cut back now and will start to show in late spring. If the new shoots are weak would that be too late to try nematodes? I have used them previously for slug control, using them during the summer for two consecutive years, and they worked well.
I do try as much as possible to avoid using insecticides and most of the time it works, but I really am a novice at it.
Thanks again to you and DovefromAbove for all your help and advice.