Uracil Herbicides | 
Uracil herbicides do not interfere with pyrimidine metabolism. In- 
stead they appear to act as strong inhibitors of the photochemical reac- 
tion of isolated chloroplasts [the Hill reaction] (Hilton et al., 1964). 
Ureas 
Monuron (3-[{p-Chlorophenyl]-1,1-dimethylurea) 
Fenuron (3-phenyl-1,1-dimethylurea) 
Diuron (3-[3,4-Dichlorophenyl]-1,1-dimethylurea) 
Ureas were inactivated by the action of ultraviolet light (Welker 
and Holm, 1959; Weldon and Timmons, 1961; Jordon et al., 1964a, b) and by 
reaction with FMN in plants (Sweetser, 1963). After exposure of N'-(4- 
chlorophenoxy) -phenyl-N,N-dimethylurea to ultraviolet radiations thin- 
layer chromatography revealed small amounts of the mono- and demethylated 
derivatives (Geissbuhler et al., 1963b). 
Degradation by soil microorganisms apparently appeared to be the pri- 
mary cause for disappearance of the urea herbicides (Hill et al., 1955; 
Reid, 1960). Some studies showed that ureas were demethylated step-wise 
and degraded to the aniline derivative (Rahn and Baynard, 1958; Geiss- 
buhler et al., 1963b; Dalton et al., 1965; Borner, 1965). 
Zea mays, Vicia faba, Phaseolus vulgaris, Galinsoga parviflora, and 
Polygonum convolvulus were exposed to labeled N'-(4-chlorophenoxy) -phenyl- 
N,N-dimethylurea. After column and thin-layer chromatography, N'-(4- 
chlorophenoxy)-pheny1-N-methylurea and N'-(4-chlorophenoxy)-phenylurea were 
identified by infra red. Evolution of labeled CO5 was observed, indicating 
metabolism to the p-chlorophenoxy-p'-aminobenzene. Using column chroma- 
tography, a compound was eluted on the position of N,N'-bis(4,4'chloro- 
phenoxy)urea (Geissbuhler et al., 1963b). 
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