Postemergence Action of CIPC

Postemergence application of isopropyl N-(3-chlorophenyl) carbamate (CIPC) killed small seedlings or redroot pigweed (A mnaranthus retroflexus L.), large crabgrass (Digitaria sanguinalis L.), and pale smartweed (Polygonumn lapathifolium L.). However, the apparent mode of action in redroot pigweed and large crab- grass was different from that in pale smartweed. The first two species showed injury symptoms 1 to 2 days after spraying, while the effect of the herbicide on pale smartweed was slow and no growth inhibition was observed until about 2 weeks after application. Injury symptoms of smartweed were different from those of the other two species. Tolerance of redroot pigweed and large crabgrass to CIPC increased rapidly with age. Studies on respiration, C140, fixation, and chlorophyll content showed that the fast action in redroot pigweed and large crab- grass was accompanied by a reduction in photosynthesis, decrease in chlorophyll content, and increase in respiration. In pale smartweed, where slow action of CIPC took place, there was no change in carbon dioxide fixation, chlorophyll content, or oxygen uiptake until about 2 weeks after spraying, when symptoms of this type of action were first observed.