I have a huge Mealy Bug infestation in my poytunnel- I didn't see it happening because they were working on and perhaps came in on the roots of a Laksa plant which it about 5ft hight and spreads to a good 5 ft too. So i didn't see it until the plant started to die. I really should get some glasses
Then I realised it was on some of the exotic vining plants too, even the roots of dock weeds even on the roots of the tomato plants.
I started going round with surgical spirits and dabbing the critters I could see individually. But that was before I realised the scale of the problem and they are in the roots.
Anybody know any solutions?

I've been searching the net but they are mostly about house plants - this is on a different scale all together.

Apologies, but I am not the bearer of good news!
We had/have a similar problem and have been unable to eradicate them for years. We resort to manual control now and the best we hope for is to keep them at a manageable level. Most pesticides are only effective for a short period when the larvae are migrating from the egg cluster (when the cotton balls start spreading out), and if growing a wide variety of plants it is impossible to find a single pesticide that is ok for everything. There are biological controls available but we had real problems getting them to stay (they just flew away). My best suggestion is to keep on top of them until the polytunnel is at it's least full in the winter and clean everything down as scrupulously as possible, squashing the blighters.
I will watch this thread and hopefully someone will post some better ideas that we can both benefit from.