Formulated and technical grade HOE-39866 [ammonium-(3-amino-3-carboxypropyl) methylphosphinate] at concentrations of 10–1, 10–2, and 10–3M were applied to leaf blade tissues of nonreproductive adult redroot pigweed (Amaranthus retroflexus L. # AMARE) and fall panicum (Panicum dichotomiflorum Michx. # PANDI). Tissues were sampled at regular intervals after treatment and prepared for light microscopic examination. The major response of both species involved rupture and contortion of the interveinal mesophyll cells with concomitant disorganization of the bundle sheath cells. Rapid epidermal collapse occurred in redroot pigweed but not in fall panicum. The absence of adjuvants resulted in nonuniform symptom expression as herbicide droplets accumulated in depressions and along leaf margins. No other adjuvant-specific effect was observed. Herbicide concentration did not alter the final response but the time-to-expression increased as concentration decreased.
