Be careful when using Copper sprays around ferns as direct spray onto them or significant drift of spray will burn the fronds off. Generally ferns need minimum spray but if you notice mealy bug or thrip use a recommended mite mixture about half the recommended rate.
The other curse is the Passion vine hopper (darkish opaque wings, total body shaped like a vampire jet) which lays its eggs at the tip of fronds like Dicksonia fibrosa and causes the ends to brown off. A pyrethrum spray (Garlic/pyrethrum mix you can buy at stores) will rid them for a time - they usually fly about November to january.