N-1-naphthylthalamic acid (NPA), 3-amino-2,5-dichlorobenzoic acid (amiben), and the dimethyl ester of 2,3,5,6-tetrachloroterephthalic acid (DCPA), in granular and liquid or wettable powder formulations, were applied to the soil and then activated by either overhead or sub-irrigation.
Granular formulations of the herbicides were as effective as liquid formulations for weed control, providing there was ample moisture for activation. High temperatures and dry soils were conducive to losses by volatilization of NPA. DCPA underwent less loss by volatilization at high temperatures. Both overhead and sub-irrigation were effective in activating these herbicides, but overhead generally was more effective. Under sub-irrigation, use of a granular carrier was more effective with a volatile herbicide. Formulation differences decreased in importance under overhead irrigation. Under conditions of high temperatures and soil moisture, soil persistence of the herbicides varied inversely with their volatility.