On 03/02/2018 13:07, Pebs wrote:

Charlie, thanks again for your help. Re. the suggestion that vine weevils "can be effectively and safely treated by using nemotodes", I forgot to provide some hopefully helpful information.

Using nematodes was one of the first "remedies" we turned to. Because we have so many tubs, and big ones too, containing Portuguese Laurels, the purchase of nematodes was expensive. No matter, we bought what was needed and used it. What's more, we repeated the procedure twice in the first year. It simply didn't solve the problem. When we dug out one tub that had been well and truly saturated with water containing nematodes, and the right saturation too, we were aghast to find the soil beneath the roots wriggling with vine weevil grubs!

In the second year we saturated the soil in the tubs with Bugclear Vine Weevil Killer! That seemed to make the weevils a bit dizzy. We began finding the odd one lying on its back on the paving around the tubs - after having munched on the leaves, and taken in some of the systemic killer. But it absolutely did not eliminate the populations.

Did some research on this. A study by University of Swansea researchers found that AT LEAST ONE THIRD of the nematodes in a pack are dead upon arrival! But more telling was that in 2016, the year in which our street was infested by vine weevils, Lord Heseltine called a "Vine Weevil Summit" of experts to gather at his estate and discuss how to deal with the problem . . . as clearly NO effective deterrent exists. There's a video of one of the presentations online.

Basically regulations about insecticides mean that there is currently nothing truly effective on the market! And I'm afraid that our determined shaking of the bushes each night while the weevils were feeding only reduced the population: it didn't eliminate them. This is why we were hopeful that a couple of really cold snaps this winter might kill them off, but you think not, and I think you're right. There are sheltered corners in this street, below gas flues etc., where a weevil or grub will have survived, and the rate at which they multiply is horrendous. One vine weevil lays 100s of eggs.

Pebs.


It doesn't help that they are all girls so don't even have to waste time
looking for a mate!

surprised at your poor results with the nematodes, we took part in the
original trials with Cambridge university back in the early nineties, it
pretty much wiped them out, we stopped using it after it went commercial
as being in cornwall we needed to be supplied early and they used not to
supply until May.
There are very effective chemicals for control (although its true the
best have been withdrawn) but they only work when added to the compost
and are designed to nobble the grubs when they are newly hatched see
MET52 (organic) and IMADASECT (Chemical) (before damage occurs) No
insecticides currently work on the adults.

Since these weevils can not fly and have to come down to the ground to
lay eggs and move between bushes Toads and Frogs are very keen on them.
I am not sure changing the plants will work, there are not many things
they wont eat the roots of/off

--
Charlie Pridham
Gardening in Cornwall
www.roselandhouse.co.uk