Posted: 01/08/2017 at 19:16
Ants don't damage plants in the way other 'pests' do - it's their tunnelling below the plant which is the issue as it causes large holes around roots, which are then sitting in fresh air. The plant has no soil medium below and around it, causing it to collapse and die.
If you thoroughly soak the plants ( do the whole hedge if necessary) it should encourage the ants to go elsewhere, as they like nice, dry conditions. Do that every couple of days over the next week or so and check to see if the ants have moved on. Although lavender can cope with drought, it doesn't mean they can't cope with water, so it won't do the plants any harm - assuming you have them in a suitable site, with decent drainage. You can then address the holes around the plants by adding new compost/soil etc.
Drainage caused by ants however, is drainage taken a step too far
I'm also assuming there isn't another issue there with the plants, of course.