I’ve been using Scaffolder’s Debris Netting over my Brassicas for years (in the fact the netting has lasted for years, which is a bonus). It has a relatively fine mesh, which keeps the Cabbage White Butterfly off the plants, and is relatively cheap to buy (70gsm 3M wide is 74p/M). The alternative is something like Enviromesh which is relatively expensive (2.6M wide is £2.34 / M).
The number of pests that I need to keep off my crops seems to be, sadly, increasing. I’ve been using Enviromesh over my Carrots for many years. Folk law says that the Carrot Fly cannot fly very high, so just a barrier 2′ high is sufficient. Sadly that’s hogwash! although I’m sure it is partially true the problem is that just one or two Carrot flies can do enough damage to the crop to wreck it, so to my mind it is pointless to grow the crop with no or minimal protection, nor with a “deterrent” companion crop – and nor with a Resistafly or similar variety which is resistant to Carrot Fly (and a compromise on flavour). Far better to prevent the fly getting anywhere near the crop, so it needs a complete enclosure of enviromesh (Carrot fly is small enough to get through Scaffolder’s Debris Netting), and it needs to be carefully secured at ground level because the fly will crawl towards the lovely smell of sweet carrots!
Note that people who tell you they use a low barrier / companion planting and never have a problem may not actually have any fly either! I work on the basis that discovering that you have NOW got fly, because your crop is ruined, is too late and wastes a year’s effort growing the crop. If you harvest all your carrots early (in particular you don;t leave them in the ground to harvest into winter) then you might avoid damage by Carrot fly.
So that’s Carrots taken care of for the last umpteen years … or so I thought.
There is increasing prevalence of Allium Leaf Minor and Leak Moth which attacks Garlic, Onions and Leeks. I’d not heard of it until recently, but I’ve decided not to wait until my crop is decimated – that would be a terrible waste of time growing the crop for a known, avoidable, pest to then demolish it – so those crops too will be covered in Enviromesh this year.
The good news, such as it is!, is that Carrots, Leeks, Onions and Garlic don’t grow very tall, so I don’t need a significant width roll of enviromesh to cover them safely.
I wrote an article some years ago about how my, then, 9 year-old built a frame for protecting my Brassicas with Blue MDPE Water Pipe hoops and Sccaffolder’s debris netting [LINK]
And here’s a link to Enviromesh (actually they now seem to be selling Veggiemesh, same sort of thing)