Conserving water by antitranspirant treatment of phreatophytes

A wax‐based antitranspirant (AT) was sprayed on leaves of three phreatophytes, salt cedar ( Tamarix sp. ), cottonwood ( Populus sp.), and willow ( Salix sp. ), as an alternative to eradicating them to conserve water. Scanning electron micrographs gave information on the nature of the foliar surfaces and coverage by the AT wax. A 10% solution of AT (vol/vol) reduced the transpiration rates of container‐grown phreatophytes by 35–75% 1 day after spraying and by 17–56% after 4 days. In gas exchange studies with salt cedar in the field, transpiration was reduced 40% by a ‘light’ application of 6% AT and 70% by a ‘heavy’ application. The AT also increased resistance to water vapor diffusion and the water potential of the sprayed leaves. On salt cedar, phytotoxicity occurred at high temperature and solar radiation only if spray applications were very heavy. The AT conserved water much more effectively when it was applied to the outer part of the canopy than when it was applied to the inner shaded foliage, where transpiration was already minimal. These data from sprays applied from the ground provided a basis for trials of AT application by aircraft.