Hi,
1) Yes, you can use wild bracken.
Look for the photos of bracken in the JADAM Organic Farming book and also in the 100 Herbs book.
If you have a different kind of fern, you can test it.
Make JHS with the fern you have, mix it with JWA and soft water in the correct proportions according to the JADAM Pest and Disease Control book, and spray a small area of your garden infested with pests.
Wait up to 3 hours to see if it kills the pest that you want to control.
It is best to spray either in the early morning, late evening, or when the day is cloudy. The longer pests stay wet and coated in pesticide, the more effective it is.
2) Bracken is effective against most pests.
In some cases, bracken is weaker than ginkgo berries, so if bracken does not work, test a more concentrated solution.
For example, to control thrips use bracken JHS and JWA both diluted at 1:25.
Concentrated JWA can damage flowers and young hairy fruits in greenhouses, so always test on small areas first.
