Off target impacts can occur as a result of NIS management practices, both chemical and non-chemical. For example:

  1. Sheep have been employed to eat leafy spurge. They have eaten some of the leafy spurge, but have also had the off target impact of soil compaction and loss of other vegetation cover that has led to erosion.
  2. Spotted Knapweed has been sprayed with 2-4 D. Cover of this NIS has been reduced, but the herbicide has had the off target impact of damaging some plant species of critical value as wildlife forage.

Off target impacts do not always occur, but it is a good practice to be mindful of them since they often have negative effects on overall land management goals. Here are a few ways to assess and be aware of off target impacts:

  1. If you are concerned about a particular off target impact (e.g., damage to native plants), take measurements of that attribute before and after management in the same way that you measure the NIS before and after management to evaluate management effectiveness.
  2. Be sure to also have an un-managed control – as there can be changes over time that are not related to your management but something else. In such situations if the both the managed and un-managed plots alter in the same way, this does not represent an off target impact due to management.
  3. Even if no off target impacts are anticipated, still be observant and aware of changes to the landscape after management is enacted. Is erosion increased? Are certain types of desired vegetation being damaged? Have patterns of use (by wildlife or domestic stock) changed in an unfavorable way? There are several other questions you could ask. A good way to look for off target impacts is to consult your general land management goals and decide if your NIS management has interfered with these land management goals in any way.


As with invasion rates and management effectiveness, off target impacts can also vary with PO. Because of this, a management strategy that might have unacceptable off target impacts in one area may have no off target impacts in another. This is one more useful piece of information that you can use to develop your management strategy.