Garden School:


Garden School:
Teaching this week: Nothing: my Trainee is on holiday!

Friday, 28 August 2020

Vine Weevils - evil little beasties!

 I've written in the past about Vine Weevils  and, following on from that post, I had an email from Susan ("Hi, Susan!") asking some follow-up questions.

Susan explains that she has a small shady front yard, filled with Astilbes which have not been performing well, despite being in conditions which they are supposed to like.

She wondered if they were in need of lifting and splitting - sometimes you do find that oldish clumps of perennials flower less and less enthusiastically, but they can be rejuvenated by the classic "lift, split, replant the newer bits from the outside of the clump, discard the inner, tired old bits" routine.

But,  horror of horrors, when Susan did this, she found that the roots were infested with Vine Weevil, which explains why the Astilbe were suffering. It's hard to flourish, when the weevil grubs are eating away all your delicate (and very necessary) roots.

 Now at this point, I would say that if you have no idea what Susan and I are talking about, go back up to that first line, follow the link, read all about Vine Weevils, then come back and carry on.

 So, is everyone with me? We all know what they are now, how they reproduce, and what to do if you find them? Great, on with the show!

 This left Susan with a pile of questions, starting with  the obvious one, can she save the Astilbes? I would say, hopefully yes: if they were mine, I would do the total removing of the soil - as per the article - and cleaning of the roots, then I would pot them up, with clean bought-in compost, and put them somewhere a long way away from the "infected" area, and preferably on a raised bench or plant stands. 

 This will give them time to recover, and also will give you a chance to check whether you got rid of all the weevil grubs and eggs.

Susan's next question was about suitable replacements, if the Astilbes were gone for ever: and the answer is, well,  anything similar which you plant there, will probably suffer a similar fate, so you might as well stick to the Astilbes.

Although having said that, some plants are more susceptible than others, so if you have plants which appear to be quite undamaged - Susan mentions ferns, and Day Lily (which I assume is Hemerocallis) which are fine - then it might be worth getting more of those, instead.

"Will the adults walk across the driveway and attack my neighbour's yard?" asked Susan. Yes. They will. They can't fly, thank the lord, but they are strong walkers, and very good climbers. There is every possibility that they walked over to her garden from that of her neighbour in the first place!

 A very sensible question is "Will the grubs starve if I don't replant until next year?" and the answer is yes: if you lift out every plant in the area, dig over the soil very thoroughly, then leave it bare, which allows time for the birds and small mammals to eat up any grubs that you miss, then yes, they should all die off. Without roots to eat, the grubs will die. But it's a bit sad to have to leave a whole area bare, for several months, and there is still the possibility that the adults will be lurking elsewhere in the garden, and will sneak back as soon as you replant.

So what does that leave? Chemical warfare, and biological warfare, as per the other article, and then ceaseless vigilance!

Susan, I hope this helps!


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