Investigations were carried out with Scheduler Plant Stress Monitor in irrigation planning, during 1989 and 1990 growing seasons under Hungarian climatic conditions. The use of instrument resulted in a 53 and 51.5 per cent increase in yield during the 1989 and 1990, respectively. The effect of convective heating was characterized by windspeed measurements above the canopy. The relationship between the stress index and windspeed was linear, irrespective of different water levels. The instrument use is effective mainly during dry seasons, when the irrigation of plants is necessary.