Effects of Herbicides on Respiration of Red Pine Seedlings. II. Monuron, Diuron, DCPA, Dalapon, CDEC, CDAA, EPTC, and NPA

Abstract

Effects of commercial formulations, inert ingredients, and active ingredients of various herbicides on respiration of young red pine (Pinus resinosa Ait.) seedlings were evaluated. Oxygen uptake at the radicle development stage was determined by the direct Warburg method. Commercial formulations of monuron, diuron, or DCPA at 4,000 ppm did not affect O2 uptake. A slight decrease in rate of O2 uptake occurred after treatment with commercially formulated dalapon at 4,000 ppm. By comparison, commercial formulations of CDEC, CDAA, EPTC, and NPA at 4,000 ppm inhibited O2 uptake greatly. Inert ingredients of CDEC at concentrations equivalent to those in the 4,000-ppm commercial formulations reduced O2 uptake significantly, and those of CDAA or EPTC appeared to cause delayed inhibition of respiration. Concentrations of the inert ingredients were 4,600, 4,500, and 1,300 ppm for CDEC, CDAA, and EPTC, respectively. At a 4,000-ppm concentration the inert ingredients of CDEC or EPTC caused appreciable reduction of O2 uptake, whereas those of CDAA showed a possible delayed inhibitory effect. High concentrations of the inert ingredients alone, therefore, could inhibit respiration of young red pine seedlings. After pretreatment with the active ingredient alone of CDEC, CDAA, EPTC, or NPA at 4,000 ppm for 1 hr, O2 uptake of pine seedlings decreased appreciably over controls. In a short-time treatment, the active ingredient of EPTC or NPA appeared to be responsible for inhibition of O2 uptake. In contrast, the inhibitory effects of the active ingredient of CDEC or CDAA could not completely account for respiratory inhibition by their commercial formulations, indicating that the inert ingredients enhanced the effects of the active component.