Can I use pest control smoke dispenser in Greenhouse now

I didn't know you could still buy those. It would depend on what plants you have growing in there and what the product is, always read the label and follow the instructions. Years ago I used to use them but only in an empty greenhouse, I would never use them for anything edible but in those days they actually contained chemicals that killed off bugs.

What is it you are growing in there and what are the pests?

 

Whitefly would leave that sticky honeydew on the leaves, they don't make holes so I guess it will be something else. Also whitefly are pretty obvious fluttering around. I think its more likely slugs or caterpillars, which I had last year on my tomatoes. They are very difficult to spot as they hide really well, its worth searching for them first as once you spot them they are easy to remove by hand - or just remove the complete branch and discard if the damage is to one area.