Bioassay Method for Determining 2,4-D in Plant Tissues

The method was based on the minimum dosage of 2,4-dichlorophenoxyacetic acid (2,4-D) that would produce strap- ping or cupping of cotton leaves. Dilutions of an unknown were applied to cotton cotyledons. The minimum dosage required to produce strapped or cupped leaves two weeks later was approxi- mately 0.05 tg/plant. The results of this bioassay were comparable to tracer methods, but the latter can detect smaller quantities of 2,4-D.