Response to Tebuthiuron by Utah Juniper and Mountain Big Sagebrush Communities

Abstract

The herbicide tebuthiuron was applied aerially in replicated parallel strips at rates of 0, 1.3, 2.0, and 2.7 kg/ha a.i. (active ingredient) in 40% pellets on a Utah juniper stand, and at rates of 0, 0.6, 1.0, and 1.3 kg/ha a.i. in 10% pellets on a mountain big sagebrush stand. Crown kill on Utah juniper was nearly 100% at application rates of 2.0 kg/ha or greater. Control of mountain big sagebrush was obtained at rates of 0.6 kg/ha and above. Antelope bitterbrush, hairy low rabbitbrush, and gray horsebrush responded to the herbicide similarly to Utah juniper. Rubber rabbitbrush was not controlled by tebuthiuron. Total understory production had changed little 3 years after application, although compensating decreases in production of perennial plants and increases in production of annual grasses occurred. Seldom does rangeland offer an array of plants that is ideal for a particular purpose (Stoddart et al. 1975). The species mixes are often changing as part of successional trends and such changes are often not in the direction that the land user desires. In pinyonjuniper and sagebrush ecosystems, the trend is often an increase in woody plants at the expense of herbaceous plants useable as ruminant forage. Such a trend may occur as a result of some action by man or his grazing animals or may be part of a normal progression toward a climatic climax. If a rangeland is to be held at a particular stage, periodic manipulation of vegetation may be required to reset the successional clock. Tebuthiuron (N_ES-( 1 , ldimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N'dimethylurea) has shown promise for controlling many woody plants. South Texas mixed brush (Scifres et al. 1979), blackjack oak (Quercus marilandica Muenchh.) and winged elm (Ulmus alata Michx.) (Shroyer et al. 1979), sand shinnery oak (Quercus havardii Rydb.) (Pettit 1979), and various other hardwood species (Nolte et al. 1982) have been successfully controlled by tebuthiuron. Control of woody overstory species often has resulted in substantial increases in forage plants about 2 years after application of tebuthiuron (Scifres and Mutz 1978, Scifres et al. 198 1 b, Jones and Pettit 1982). Generally, the junipers have been unresponsive to tebuthiuron. Negative results have been reported on western juniper (Juniperus occidentalis Hook.) (Britton and Sneva 198 I), eastern red cedar (J. virginiana L.) (Scifres et al. 198 la), and redberry juniper (J. pinchotii Sudw.) (Ueckert and Whisenant 1982). However, tebuthiuron has been shown to be effective in controlling Utah juniper (J. osteosperma (Torr.) Little) at rates of 2.2-4.5 kg/ha (Johnsen 1977, 1979). Sand sagebrush (Artemisia filijiolia Torr.) has been effectively controlled (Jones and Pettit 1982). Control of big sagebrush has been obtained at rates of 1.1 to 2.2 kg/ha (Britton and Sneva 1983, Klauzer and Arnold 1975). Authors are supervisory range scientist and range conservationist, Shrub Sciences Laboratory, Intermountain Forest and Range Experiment Station, Provo, Utah 846Ol;and rangeconservationist, Fillmore Ranger District, Fishlake National Forest, Fillmore, Utah 8463 I. Authorsacknowledge Richard Bjerregaard and Eli Lilly and Co. for theircontributions to this research. The use of trade, firm. or corporation names in this article is for the information and convenience of the reader. Such does not constitute an official endorsement or approval by the U.S. Department of Agriculture of any product or service to the exclusion of others that mav be smtable. This article reoorts research involvinn pesticides. It does not contain recommendations for their “‘se! nor does it imply thay the uses discussed here have been registered. All uses of pestlcldes must be registered by appropriate State and/or Federal agencies before they can be recommended. Manuscript accepted April 17, 1984. 56 Cool-season herbaceous plants typical of the Intermountain region appear to be sensitive to tebuthiuron and may be strongly repressed by rates of 2 kg/ha (Britton and Sneva 1981, 1983). The pinyon-juniper zone, dominated by Utah juniper, and the sagebrush zone, dominated by big sagebrush (Artemisia tridentata Nutt.), are major plant types in the Intermountain region. Combined, they occupy 34% and 4.5% of’Utah and Nevada, respectively (USDA Forest Service 1972). These plant types, whose historic use has been dominated by the grazing of livestock, have experienced increases in amounts of woody plants and diminished amounts of herbaceous forage plants. In an effort to reverse this trend, managers have tried fire, mechanical, chemical, and biological means to manipulate vegetation. The objectives of this study were to determine the effectiveness of tebuthiuron in controlling woody plants on Utah juniper and mountain big sagebrush (Artemisia tridentata ssp. vaseyana (Rydb.) Beetle) dominated sites and evaluate response of herbaceous species.