Some greenhouse questions

Here's an infestation I prepared earlier

One of my tomato plants has leaves that look a bit like that, and some of the lower ones have been munched by something - but I can't see any beasties on them.

Hello VV,

As far as the ventillation goes I recon it's about balancing air changes (as plants need to take carbon out of the air to grow) with temperature &/or humidity control.

I've got an automatic vent opener to control the heat (which also increases the air changes). I'd recommend one - but not a Jemp Vent as they fail after a short time. I've also got a few polycarbonate panels (used to replace the odd broken pane) that have louvre vents fitted to them (cheapo ones from local hardware shop)..placed at different heights it helps air circulation..or so I think.

I only grow toms in my greenhouse & keep the door closed to keep out blight that seems to claim everyone elses toms - it's worked so far...but I think different plants like different humidity/heat so you may need to experiment.

It must be such a luxury to have such a big greenhouse...I'm not envious..much.

I agree, I think being able to leave the door open, to cool the greenhouse, is important, so perhaps some sort of netting that you can use to keep the critters out?

Even just something propped against the doorway - such as weld-mesh (assuming they won't hop/fly over it)

I don't think one of those door-way vertical-streamers would do as my guess is that it would not allow enough air though.