Bruchidius villosus beetle
Biological control agents such as the Scotch broom seed beetle Bruchidius villosus are regulated and distributed by the Oregon Department of Agriculture. Their website indicates that this beetle is widely established across the state - in fact, it may already be present on your site.
It's important to note that biological control agents will not eradicate a problem weed; rather, they can help to keep the population in check. This beetle will not do anything to established Scotch broom plants. They will predate on a fraction of the seeds produced. Scotch broom is a difficult weed that usually requires a combination approach to control. Herbicides and mechanical or manual control methods are also appropriate. If you are wishing to establish trees or crops on the 5 acres, you will need to rely on something other than biological control to get rid of the Scotch broom.
Here are some useful links: