The New Zealand Plant Conservation Network

Greetings, need some technical information about the control of this species, other than pesticides like Roundup, since the control it's meant to be done in a delicate and protected enviorment.

I've not had any experience controlling large sites, only small sites where hand removal of corms is possible.
The Weedbusters site has information for chemical control of larger infestations: http://www.weedbusters.org.nz/weed-information/crocosmia-x-crocosmiiflora/59/

Thanks, but since it's a protected area, we can`t use any commercial pesticides

Hmm, well that's a challenge. You could try to rot it out by smothering it with polythene sheets (but this would be pretty unwieldy in a large site, especially if shrubs and other desirable plants present). I've of people successfully killing large pampas grasses by smothering them in thick sheets of plastic and leaving it for a year.