Turpentine (Eremophila sturtii) control by mechanical uprooting

Abstract

Turpentine (Eremophila sturtii R.Br.) is a tenacious shrub that negatively affects rangeland, and is difficult to control by fire, herbicide or mechanical methods. When above-ground growth is removed, it sprouts vigorously from underground buds on the root system. Uprooting or grubbing is the removal of a shrub and its root crown with a U-shaped blade. Our hypothesis, that depth of uprooting and covering of all exposed roots with soil would influence regrowth, was tested using 100 shrubs divided into five treatments of 20 shrubs each. Each of two depths, 10 and 25 cm, were divided into roots covered and roots exposed. The fifth treatment was uprooting at 25 cm with an extra-wide blade to increase lateral root cutting, and roots were covered. Uprooting depths could not be kept constant and varied from 9 to 33 cm. Plots were evaluated 30-months post-treatment. Roots covered with soil had significantly greater plant mortality (P = 0.001) compared with roots exposed at all depths, when grouped from either 9 to 33 cm, 9 to 19 cm, or 20 to 33 cm. When all depths were grouped, mortality was 82% for plants with roots covered and 5% for plants with exposed roots. Results with the extra-wide blade were not different from uprooting with the narrower blade. These data suggest that the efficacy of commercial uprooting could be improved by covering the roots with soil. A study to determine rates of grubbing at different plant densities was also included. A 30 kW, farm tractor with a rear-mounted grubbing blade was used. Based on the prediction equation, grubbing rates for 200, 300, and 400 plants/ha would be 1.08, 0.82, and 0.69 ha/h.