The two photographs below demonstrate the first time I have had an herbicide help in identifying a plant. The bottom photograph was taken several years ago to show the diagnostic purple bands that appear only on Jungle Rice, Echinocloa colona, a close relative of barnyardgrass. In fact, members of the genus Echinochloa are known to cross amongst themselves producing hybrids that are difficult to identify. When the purple bands appear on what looks like a barnyardgrass seedling it is Jungle Rice. However, frequently the purple bands do not show up. If you look carefully at the plant in the top photograph the green leaves do not show the purple banding. Only the leaves where the chlorophyll has been affected by an application of Command herbicide show the purple bands in a very striking way.