As well as drinking the stuff, you can use camomile tea in the garden and the greenhouse.
As a “pesticide” it zaps anything that pyrethrum would zap. It’s also good for preventing damping off in seedlings and, just as it can be a pick-me-up for people, it’s a pick-me-up tonic for plants.
All you need is some camomile tea – as I shop in Asda I use their camomile tea bags. Just make sure it’s 100% camomile (as Asda’s is) – avoid the teas with peppermint addins and the like. Then you need a sprayer – you can buy little pump sprayers that hold up to a litre of liquid in all sorts of places or thoroughly clean out any household sprayer like the ones shower cleaners or surface cleaners come in. But if you re-use one of these, you really need to make sure it’s cleaned out thoroughly.
I tend to make my solutions double- or triple-strength. Instead of using a single teabag to make a mugful I use two if I’m making a tonic/anti-damping spray or three if I’m making a pest-killing spray. Pour the appropriate amount of boiling water over the teabags and leave to soak for a few hours (not more than 24) to get all the goodness out of the tea. I gauge things by when the water gets cold (you’re going to have to leave it to chill anyway). Then I remove the bags and pour the solution into my sprayer. It’ll keep ok in the sprayer for about a week but don’t drink it!
As an insecticide spray as you would using any pesticide and use the same general precautions. Give the plant(s) and the bugs a good drenching, including undersides of leaves. You can also spray the surface of the compost.
To prevent damping off spray seedlings gently during a morning and leave them to dry naturally. It’s best not to spray late in the day as they will remain damp overnight which won’t help.
As a tonic feed spray the foliage until the solution just starts to run off and leave to dry naturally.
I have read that camomile tea is also good as a general fungicide but haven’t tried that yet.