The spread of herbicide resistant pigweed seems to have no bounds. An absolute weed beast, pigweed can grow up to 2 inches each day and has been recorded as high as 9 feet tall and 40 pounds in weight. Arizona was hit with its first documented case of pigweed in 2012 and farmers will be keeping a close watch on fields in 2013.

(See related: Glyphosate resistance changes Arizona cotton industry)