Examined the mode of action of aC8-C10 fatty alcohol emulsion (FAE) used to inhibit sucker growth in tobacco production. To determine its effect, near infrared spectroscopy (NIR), photacoustic spectroscopy (PAS), electrical resistance, and the capacity of cells to undergo reverse plasmolysis were used on leaf tissue from Nicotiana tabacum L. and other dicotyledonous species. NIR spectra showed that isolated cuticles were affected optically, but did not dissolve when treated with FAE. PAS absorbances in the UV of isolated cuticles and of epidermal peels were similar. PAS absorbances in the visible region were used to monitor the penetration by FAE into leaf tissue. Penetration to the subcuticular cells took approximately 2 hours. Electrical resistance of FAE-treated isolated midveins of tobacco leaves decreased with time, which indicated that the cellular membranes became leaky. The effect was confirmed with Elodea sp., where leaf celles after treatment with 1% and 5 % FAE lost the capacity to plasmolyze in a 10% solution of Ca(NO3)2. The results were interpreted to mean that a FAE suckercide passed into the tissue without disruption of the cuticle. After penetration of the cuticle, an alteration of the plasma membranes of the subtending cells occurred, as evidenced by a discoloration of the sucker tissues. With the loss of the semipermeable properties of the cell membranes, desiccation of the sucker tissues followed and necrosis was completed.