The influence of environmental conditions on tree growth and cuticular covering of leaves of apple ( Malus domestica Borkh.) was investigated in relation to spary uptake. Various interactions between environmental factors influenced growth responses. Under cooler temperatures (20°C), 75% shade reduced shoot growth and leaf number; however, under warmer temperatures (25°), shading had no effect. High soil water potential (−13 KPa) and 75% shade significantly reduced total leaf area per tree, while under low soil water potential (−33 KPa), shading had little effect. The dry weight of total leaves per tree decreased 46% as soil water potential decreased under full-sun conditions. Under shade, a decrease in soil water potential resulted in a 20% decrease in dry weight. Total stem dry weight decreased as temperature increased under full-sun conditions; however, temperature had little effect on stem dry weight in plants grown under shade. Under 75% shade, an increase in temperature decreased total specific leaf weight (SLW), while under full sun there was no temperature effect. SLW of newly formed leaves was not influenced by environmental interactions. Leaf epicuticular wax quantity increased as soil water potential decreased. A decrease in soil water potential increased the proportion of alkanes and wax esters in extracted leaf waxes. Alkane content also increased as temperature increased. The different environmental growing conditions influenced the photosynthetic mechanism and masked the effect of prometryn, a triazine herbicide, thereby rendering it unreliable as a method for determining foliar absorption.
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Darnell et al. (1983) studied this question.