Application of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) was effective in controlling quackgrass (Agropyron repens) in fields planted to corn. Corn yields were greatly improved by the treatment. Most favorable dates of application were in the fall or in the early spring before planting. Applications after corn planting were much less effective. Favorable rates of application were 2 to 4 lb/A. Rates lower than 2 lb/A were not as effective and rates over 8 lb/A were not required. Atrazine and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) were generally superior to other triazine analogues used. Greater solubility and greater activity as a foliar spray favors use of atrazine for control of quackgrass.