Whole-plant gas exchange, not individual-leaf measurements, accurately assesses azalea response to insecticides

A comparison of whole-plant and individual-leaf gas exchange measurements w as undertaken among azaleas, Rhododendron spp., treated with insecticides u sed to control the azalea lace bug, Stephanitis pyrioides (Scott). Azaleas in individual-leaf trials received 3 insecticide treatments during three 21 -day trials. The whole-plant study included 2 insecticide treatments and wa s conducted during a 21-day trial. Individual-leaf studies indicated that i nsecticidal soap and acephate application at higher than recommended rates caused short-term reductions in gas exchange. However, variability among in dividual-leaf measurements prevented consistent conclusions. Whole-plant ga s exchange measurements provided consistent results and confirmed that inse ctidical soap caused short-term reductions in P-net and R-dark. Additionall y, whole-plant gas exchange measurements enabled growth analyses and demons trated a reduction in carbon use efficiency attributed to insecticidal soap treatments. Neither acephate nor horticultural oil significantly affected whole-plant gas exchange. Gas exchange parameters for treatments in all tri als were not significantly different from the controls by Day 21. (C) 2000 Elsevier Science Ltd. All rights reserved.