On Friday, 5 February 2016 19:25:43 UTC, Mathew Newton wrote:
You mention leatherjackets, which is plausible, though this would be a
major infestation.

I've just dug out a mugful of soil and found 2-3 grubs. If that density is uniform I guess this could be regarded as 'major'?

More like 'typical', I'd have thought. You could try covering a couple of square metres with carpet and black sheeting for 24 hours when the soil is damp. If, when you take it off, you have a couple of hundred leatherjackets, that would be bad. If you have ten, that's normal.

Did you notice a lot of crane flies about at the end of last summer? If you had a major infestation I't expect a lot of birds feeding on the lawn, digging in the soul. Up to and including woodpeckers, they are very good at finding them.

I think that purveyors of 'treatments' overstate the leatherjacket menace.