Response of Seedlings of Three Perennial Grasses to Dalapon, Amitrole, and Glyphosate

Differential tolerances to dalapon (2,2-dichloropropionic acid), amitrole (3-amino-s-triazole) plus ammonium thiocyanate, and glyphosate [N-(phosphonomethyl)glycine] of 3- to 10-week-old seedlings of creeping red fescue (Festuca rubraL. ‘Boreal’) and redtop (Agrostis albaL.), which are desirable ditchbank grasses, and reed canarygrass (Phalaris arundianaceaL.), a troublesome ditchbank weed, were evaluated in the field. Within each of four treatment dates (growth stages), dalapon affected all species similarly; effects among treatment dates ranged from none to severe. Amitrole at 4.5 kg/ha plus ammonium thiocyanate at 4.1 kg/ha reduced the stand of 3-week-old seedlings of redtop, creeping red fescue, and reed canarygrass by 0, 42, and 94%, respectively, but had little effect on older seedlings. Glyphosate at 1.1 kg/ha did not significantly reduce the stand of 5- to 10-week-old creeping red fescue seedlings, but killed nearly all reed canarygrass seedlings. Redtop was intermediate in its tolerance to glyphosate. Applications of amitrole plus ammonium thiocyanate or glyphosate should be effective in converting ditchbank vegetation from an undesirable stand of reed canarygrass to a desirable stand of redtop and creeping red fescue, respectively.