Transpiration Reduction of Shrub Live Oak by Picloram

Abstract

Transpiration-retardant properties of picloram (4-amino-3,5,6-trichloropicolinic acid) were evaluated for utility in water conservation projects in the chaparral vegetation type. A subirrigation volumetric technique with potted plants was used to investigate the effects of sequentially applied foliage sprays on shrub live oak ( Quercus turbinella ). The treatments proceeded from low-dosage and low-volume sprays to high-volume sprays in which the soil was shielded to prevent root uptake. A single spray of 0.56 kg/ha in 93.5 liters (0.5 lb/A in 10 gal) temporarily reduced transpiration approximately 20 percent, without visible leaf injury. Two additional treatments at the same dosage reduced initial transpiration 36 percent and caused 13 percent leaf injury. A fourth treatment of 2.24 kg/ha in 374 liters (2 lb/A in 40 gad reduced initial transpiration 51 percent accompanied by 27 percent leaf injury. A final wetting spray with the same mixture caused rapid and complete reduction in transpiration, but killed all leaves. The antitranspirant effect of picloram at sublethal dosages on shrub live oak is too slight to be hydrologically significant. Forest Sci. 24:217-221.