Some weeds produce long-lived seeds and the vicinity of kill sites must be inspected and often retreated for many years. As the number of patches and patch size increases, the opportunity for total eradication may slip away. Thereafter, containment or preventing the spread by eradicating the pioneering weeds in surrounding lands becomes a more costly but still necessary long-term job. For surveillance to be effective, one must be able to identify new weed threats. It is most effective when new invaders can be identified before seed set or even flowering.
Prevention focuses on keeping seeds out and keeping rangeland vegetation healthy.
While invasive weeds can spread into healthy rangelands, reducing weed seed production with competition can generally diminish the rate of weed spread. Enhancing competition from natives allows fewer and more marginal safe sites for new weed plants. For each weed there may be high and low probability methods of spread. All these vectors are more significant when they come from weed infested areas. While only some of these can be prevented, one should always ask if the weeds that can be are being prevented from moving.