Appendix B. Direct effects of insecticide on plant performance.
We conducted an experiment to determine if insecticide (carbaryl) application had any direct (beneficial or phytotoxic) effects on plant performance. In 2005, we transplanted 20 tree cholla (~ 0.5 m height) into pots directly from our field site and brought these plants into a greenhouse at the Sevilleta NWR. We measured the lengths of all new stem segments initiated by each plant on May 21. Potted plants were then randomly assigned to insecticide or water treatments, and these treatments were applied every two weeks throughout the 2005 growing season (synchronized with the field experiment). We measured stem segments again on September 6. For each plant, we summed lengths over all stem segments and measured relative growth as the difference between finial and initial total stem segment length, divided by the initial value.
We found that growth in the greenhouse, where all plants were protected from herbivores, was similar between insecticide and water treatments (mean [SEM] insecticide: 4.37 [0.91], control: 5.69 [1.23]) and did not differ statistically between treatments (t18 = 0.86, P = 0.39). We conclude that application of carbaryl had no measurable, un-intended effects on plant growth.