Soil applications of α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), O,O-diethyl S-((ethylthio)methyl)-phosphorodithioate (phorate) and their combinations did not affect cotton (Gossypium hirsutum L.) germination. Plants grown on soil treated with trifluralin were shorter than plants on soil treated with phorate. High rates of phorate reduced shoot weights. Root weights of phorate-treated plants were higher than those of trifluralin-treated plants but lower than those of the controls. In culture solution and soil, trifluralin inhibited lateral roots of cotton. In the presence of phorate, trifluralin-treated plants produced more lateral roots than plants treated with trifluralin alone. Other organophosphorus compounds, when used in combination with trifluralin, did not increase the number of lateral roots.