Invest in some netting and a frame. That is the only 100% way to keep cabbage white butterflies away. I think you need 7mm for the smaller cabbage white butterflies. Netting is pretty safe to pets and wildlife.
The issue I see with grazers G3 is that it is not very long lasting and not 100% effective. The chart on
https://www.grazers.co.uk/products/g3/ says 48h after treatment with grazers G3 10% of the leaf was eaten. It’s not really clear what test they are doing, plants in the field or in a test box.
If they used a test box and added caterpillars which could choose which leaf to eat then maybe treated leaves are less tasteful to caterpillars so they choose the untreated leaf, but a caterpillar on your treated leaf on your plot is not going to have that choice and is still going to eat your treated leaf just as much as if it was not treated. I don’t get the impression that any caterpillars are going to set off on a hike to find an untreated leaf on an adjacent plot.
The chart only goes up to 48h so it’s difficult to know how much of the leaf would be left after 1 week? At the claimed rate of loss (10% 48h) after 1 week 30% would be gone and after 2 weeks half the leaf would have been eaten. That’s assuming you sprayed regularly and after rain etc. and you’re confident you will get every leaf top and bottom covered sufficiently?
Half the leaf gone in 2 weeks does not seem like it stopped much damage when netting can be 100% effective.
