Response of Needle-and-Thread and Western Wheatgrass to Defoliation by Grasshoppers

Field and greenhouse studies were conducted to measure changes in plant growth resulting from grasshopper defoliation. All data indicated that as grasshopper grazing intensity on needle-and-thread grass increased, total root weight decreased. A greenhouse study with western wheatgrass showed that heavy grazing (80% removal of top growth) for a 16-day period reduced top growth 82%, root growth 85%, crown growth 81%, rhizome growth 100%, and depth of root penetration 49%. Field observations indicated that most grasshopper defoliation of needle-and-thread grass and western wheatgrass occurs after seasonal growth has been completed.