Based on many years of stewardship experience in natural areas in Illinois and Pennsylvania, I discuss the potential for roadside mowing to facilitate the spread of aggressive alien plants. Along interstate highways, mowers are a potential mechanism for spread of aggressive plants for long distances. Other factors that may be important are favorable climatic and soil conditions, and positive responses by aliens to disturbances caused by mowing along these highways. This report outlines some differences and similarities between central Illinois and south-central Pennsylvania, which have similar climatic conditions but different soils and length of settlement time.