A 99% reduction is obtainable and has been documented by Jim Story of the western Montana Ag reseacrh center in Corvallis, MT a copy of this research is posted on our website under "supporting research" that took 11 years to happen and his other site in the study had a 77% reduction in knapweed density. We have seen similar results in the Missoula area. You generally do not see a decline in knapweed density for about 4 years as the bugs need to build up to a high population before they can impact the plant.
If you mow when the plant is in the bolt stage or flower bud stage, the plant will flower again at a later time. You also throw the plant out of synchronization with the seedhead biocontrols and can actually increase viable seed production. If you mow when the plant is in flower before it sets seed it generally does not flower again. However different flowers develop at different times on the same plant. Heavy watering can reduce the plant density, pulling is very labor intensive and does nothing about the extensive seed bank in the soil. The seed can stay viable for up to seven years. As for predation by chickens, turkeys etc they may get a few, if you can keep the birds away from the bugs for just a couple weeks after the first release I think they would be well established, really I think they would do OK without doing anything special but to be sure, it would be good to protect them at first after the first year you should have several thousand of them out there. Voles and other rodents are probably the greatest predator according to Jim Story who has worked on this research for over 30 years. Hope that helps.