(Scottish) Vine Weevils-when to apply nematodes?

Quercusrobur81

Hi-really sorry as this has probably been discussed many times but I am a bit worried about an infestation of vine weevil and I was wondering when best to apply nematodes? We had a bit of vine weevil damage last year and I just sort of hoped it would go away but the notched leaves are everywhere this summer, I have found quite a few and am keen to get on top of the problem ASAP! I emailed a nematode company for advice and they recommended a spring application but I’ve read autumn can also be an effective time to do it. We are in Scotland so I would like to do it before it gets too cold-is the end of this month too early in anyone’s experience? I’ve dug about around the notched hydrangeas and azaleas but not found any grubs do possibly too early? many thanks!

Jacquimcmahon

Remember the food plants for the adults are not necessarily the same as the food plants for the grubs. You will often find notched leaves on one plant but no grubs, then a totally different type of plant has its roots demolished by the grubs.

adults love rose leaves here but lay eggs in the soil around things like pansies and primavera. 

As for timing the nematodes need some warmth in the soil.

Fairygirl

Hi Elspeth - as Jacqui says, the soil needs to be warm enough for them to work. You may also have to apply a few times to get on top of the problem, and do as big an area as you can afford [they aren't cheap!]  when you do them - not just a few plants that seem to be affected. Once you get rid of the adults, there won't be so many grubs to do the root chewing though. Mature, healthy shrubs can shrug off damage, but it can be unsightly. 

I think end of this month is fine, and then do it again in April/May. Any earlier than that is too cold here. 

Quercusrobur81

Thank you both for your replies, there is evidence of them in every flower bed and I lost a couple of potted plants earlier this spring so am feeling worried! Seem to discover a new pest every summer... Thanks!

Jacquimcmahon

Potted plants are most vulnerable to the grubs as they cannot move from plant to plant, therefore they quickly decimate the root systems.

Fairygirl

They're particularly fond of Heucheras, but on the plus side, they are among the easiest plants to revive and propagate from 

Pay particular attention to your potted plants, as @Jacquimcmahon says. The b***ers love 'em.

Quercusrobur81

😬 will do, thanks guys. Wonder if they have a natural predator I could encourage into the garden, ideally something more effective than me in a head torch...

BobTheGardener

Their main predators are nematodes which naturally exist in the soil (some types of soil have more than others though.)  However, nematodes are not present in the commercial composts most of us use for potted plants, so the vine weevil eggs and grubs have far more chance of survival in pots full of MPC.  In the case of heucheras, I now pot young ones on into a 50/50 mix of my clay-based garden soil and home-made compost and haven't had any vine weevil losses for a couple of years.  I would not hesitate to use commercially bred nematodes as a first step to control such a widespread problem as the one you describe, applying while the weather is warm and wet.

Quercusrobur81

Thanks Bob, that’s interesting info-I’ve just bought a dwarf hydrangea so I’ll pot it up with some homemade compost and (I knew it would come in useful one day) some of the loam from a turf pile I made a couple of years ago!