New Zealand pastoral agriculture relies heavily on the intensive grazing of pasture. To protect both the animal and the consumer, this feedstuff must be of high quality; the detection of mycotoxin contamination is thus essential. The analysis of mycotoxin contamination of herbage feed requires robust assays which can reliably cope with this complex matrix. Conventional analysis of herbage by high‐pressure liquid chromatography, gas chromatography/mass spectrometry is at best tortuous, relying on extensive extract cleanup and purification prior to analysis to avoid matrix interferences. No routine methods exist as yet for the analysis of the trichothecenes in pasture samples. Recent advances in analytical procedures have seen the rapid development of immunoassays, such as enzyme‐linked immunosorbent assays (ELISAs), which have the advantage of simplicity, speed and sensitivity—but these too frequently suffer matrix interferences when applied to herbage samples. We describe here a simple extraction and solvent partition clean‐up procedure which minimizes the interferences caused by the grass matrix on the analysis of herbage samples for 3‐acetyldeoxynivalenol (3‐AcDON) by an indirect competitive ELISA.