Crop busting is a type of ecoterrorism directed at genetically modified crops; while many ecoterrorism attacks involve arson or industrial sabotage, crop busting is much less dangerous. It is the simple act of uprooting, trampling, felling, pruning, or otherwise destroying genetically modified crops in the field.
Crop busting is pretty harmless as such things go; it takes place in developed countries (most reports come from America, Canada, and the UK), and generally focuses on university test plots, not farmer's fields. The goal is to prevent further research, not attack the crops of misguided farmers. Crop busting seems to have peaked in 2000, and is less common now. While genetically modified crops are still an environmental issue, most ecoterrorists now seem to be focusing on the lumber industry and freeing animals.
While most crop busting is done by semi-organized groups of individuals rather than formal groups, organizations such as Earth Liberation Front and Reclaim the Genes have been known to take credit for some of the more spectacular crop busting events.