Control Of Big Sagebrush Research Articles

Sagebrush Control: At What Canopy Cover Is It Economically Justified?

We determine the economic threshold level for big sagebrush control based on 18 yr of forage-response data from an experiment conducted in Carbon County, Wyoming. We analyze the impacts of climatic variables and treatment site characteristics, such as sagebrush abundance levels, precipitation, and understory composition, on forage response and threshold level. We find that sagebrush canopy cover levels, April precipitation, May soil moisture, and understory composition are statistically significant factors in explaining forage response to sagebrush treatment. Forage yield across treated and untreated plots for 10 canopy cover levels, ranging from 4% to 40%, are analyzed via panel data regression techniques. We further investigate the impact of variability in precipitation and understory characteristics on economic outcomes of sagebrush control by analyzing three scenarios. Scenario 1 uses actual forage response data that include all variability from precipitation and understory composition. Scenario 2 uses regression-predicted yields across plots assuming average precipitation and soil moisture conditions. Scenario 3 uses regression-predicted yields assuming average precipitation, soil moisture, and understory characteristics across plots. Net present values based on value of grazing (for estimated yield differences between treated and untreated plots assuming 50% forage utilization) compared to treatment cost across sagebrush cover levels are estimated across these three scenarios. Results indicate that the economic threshold level of sagebrush infestation for the study period was between 8% and 24% for the analyzed scenarios. This indicates variability in precipitation and understory composition impact forage response and the resulting economics of sagebrush control. We conclude that range managers should consider potential control site characteristics and long-range weather forecasts when contemplating sagebrush control.

Economics and Optimal Frequency of Wyoming Big Sagebrush Control With Tebuthiuron

The optimal frequency of tebuthiuron (N-[5-(dimetylethyl)-1,3,4-thiadiazol-2yl]-N,N9-dimethylurea) treatments was investigated for Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) when added forage for livestock and wildlife are considered to be the economic benefit of the treatment. Data collected at 8 northwest New Mexico study sites were used to define key relationships for the economic analysis. This long-lived sagebrush control practice was found to be a viable investment for landowners who participate in available cost-share programs. At productive sites, where average herbaceous production increased to over 700 kg/ha following big sagebrush control, the economic value of added forage justified the total cost of the herbicide treatment. Tebuthiuron rates higher than 0.5 kg active ingredient/ha lengthened the expected life of the brush control treatment, but the extended life did not justify the added cost. The threshold abundance of sagebrush needed for economical control was found to be variable, depending on treatment cost, study site, and the economic value of forage. With a 50:50 cost-share arrangement and with forage valued at 7/AUM, the economic sagebrush canopy threshold from the livestock grazing perspective was estimated to range between 6% and 14%, depending on site productivity. A second brush control treatment would optimally be implemented before forage production was fully depleted by the recovering brush canopy. Because some native fauna are closely tied to big sagebrush plant communities and benefit from the shrubs’ presence, the trade-off in the desired abundance of big sagebrush must be weighed between economic considerations and other resource values of interest.

Economics and Optimal Frequency of Wyoming Big Sagebrush Control With Tebuthiuron

Abstract The optimal frequency of tebuthiuron ( N -[5-(dimetylethyl)-1,3,4-thiadiazol-2yl]- N,N ′-dimethylurea) treatments was investigated for Wyoming big sagebrush ( Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) when added forage for livestock and wildlife are considered to be the economic benefit of the treatment. Data collected at 8 northwest New Mexico study sites were used to define key relationships for the economic analysis. This long-lived sagebrush control practice was found to be a viable investment for landowners who participate in available cost-share programs. At productive sites, where average herbaceous production increased to over 700 kg/ha following big sagebrush control, the economic value of added forage justified the total cost of the herbicide treatment. Tebuthiuron rates higher than 0.5 kg active ingredient/ha lengthened the expected life of the brush control treatment, but the extended life did not justify the added cost. The threshold abundance of sagebrush needed for economical control was found to be variable, depending on treatment cost, study site, and the economic value of forage. With a 50:50 cost-share arrangement and with forage valued at $7/AUM, the economic sagebrush canopy threshold from the livestock grazing perspective was estimated to range between 6% and 14%, depending on site productivity. A second brush control treatment would optimally be implemented before forage production was fully depleted by the recovering brush canopy. Because some native fauna are closely tied to big sagebrush plant communities and benefit from the shrubs’ presence, the trade-off in the desired abundance of big sagebrush must be weighed between economic considerations and other resource values of interest.

Ecology and management of sage-grouse and sage-grouse habitat

Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (≥ 18 cm) and medium height shrubs (40-80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of sage-grouse habitat changed dramatically with European settlement. In high elevation sagebrush habitat, fire return intervals have increased (from 12-24 to > 50 years) resulting in invasion of conifers and a consequent loss of understory herbaceous and shrub canopy cover. In lower elevation sagebrush habitat, fire return intervals have decreased dramatically (from 50-100 to < 10 years) due to invasion by annual grasses, causing loss of perennial bunchgrasses and shrubs. Livestock grazing can have negative or positive impacts on sage-grouse habitat depending on the timing and intensity of grazing, and which habitat element is being considered. Early season light to moderate grazing can promote forb abundance/availability in both upland and riparian habitats. Heavier levels of utilization decrease herbaceous cover, and may promote invasion by undesirable species. At rates intended to produce high sagebrush kill, herbicide-based control of big sagebrush may result in decreased habitat quality for sage-grouse. Light applications of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) can decrease canopy cover of sagebrush and increase grass and forb production which may be locally important to nesting and foraging activities. The ability of resource managers to address sage-grouse habitat concerns at large scales is aided greatly by geomatics technology and advances in landscape ecology. These tools allow unprecedented linkage of habitat and population dynamics data over space and time and can be used to retroactively assess such relationships using archived imagery. The present sage-grouse decline is a complex issue that is likely associated with multiple causative factors. Solving management issues associated with the decline will require unprecedented cooperation among wildlife biology, range science, and other professional disciplines.

Composition and Diversity of Plant and Small Mammal Communities in Tebuthiuron-Treated Big Sagebrush (Artemisia tridentata)

Sagebrush control has historically involved mechanical and chemical (2,4-D) treatments designed for total control and which detrimentally affect nontarget plant species, resulting in decreases in native wildlife abundance and diversity. Tebuthiuron, a potentially selective herbicide with thinning capabilities, was applied at various rates to big sagebrush plots near Ten Sleep, WY in 1979 and Hyatteville, WY in 1983. Plant and small mammal communities were evaluated in 1992 and 1993. Big sagebrush cover in untreated areas was 31 ± 1% in 1992 and 34 ± 1% in 1993 at Ten Sleep, and 44 ± 4% at Hyatteville (α = 0.10). Big sagebrush control increased as application rate increased. Productivity of herbaceous species (graminoids, forbs, or both) tended to be greatest at about 11 to 17% big sagebrush cover. In general, plant community diversity tended to be greatest where sagebrush was thinned to this level. Small mammal community diversity was least at both sites where big sagebrush cover was less than 5%, and was strongly correlated with plant community diversity at Ten Sleep (R2W= 0.99; 4 degrees of freedom). In addition, greater abundance of or better habitat quality for endemic, stenotypic (habitat specialist) species was associated with about 15% big sagebrush cover. This suggests (albeit retroductively) that biodiversity at both local (alpha) and global (epsilon) scales might be conserved by thinning big sagebrush with tebuthiuron.

Soil-Water and Vegetation Dynamics through 20 Years after Big Sagebrush Control

Soil water withdrawal and vegetation characteristics of mountain big sagebrush (Artemisia tridentala ssp. vaseyana Rydb. Beetie) areas sprayed with 2,4-D (2,4-Dichlorophenoxyacetic acid) were measured for 20 years after treatment. Herbaceous productivity more than doubled in the first 3 years after spraying and was still twice as great as untreated vegetation 10 to 17 years after treatment. Sagebrush removal reduced seasonal water depletion 9% to a 1.8-m soil depth, equal to 2.4 cm of water. The entire difference was realized from soil 0.9-1.8 m deep. Depletion from the surface 0.9 m of soil under grass-dominated vegetation slightly exceeded depletion under sagebrush-dominated vegetation. Mathematical relationships were developed that predict the percent reduction in seasonal water depletion in relation to time since sagebrush control for soil depths of 0.0-1.8 m, 0.0-0.9 m, and 0.9-1.8 m. Mountain big sagebrush was a minor vegetation constituent on treated areas 20 years after spraying. Sagebrush density increased from 2,100 to 4,400 plant/ha between 10 and 20 years after spraying while herbaceous production ranged between 28 and 52 kg/ha. Both density and canopy cover of sagebrush on untreated areas declined significantly over the study because of the actions of a snowmold fungus.

Wyoming Big Sagebrush Control with Metsulfuron and 2,4-D in Northern New Mexico

Field experiments conducted between 1982 to 1988 compared 2,4-D [(2,4-dichlorophenoxy)acetic acid] and metsulfuron [2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino)carbonyl]amino]sulfonyl]benzoic acid) for control of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) in northern New Mexico. Precipitation was near or above normal during years of herbicide applications. Broadcast sprays of 2,4-D at 2.2 kg/ha were most efficacious during rapid shoot elongation, but mortality averaged less than 38% from treatments applied over 4 separate years. Wyoming big sagebrush shoot growth was greatest in April and May compared to other months, but growth was highly variable among shrubs and probably reduced effectiveness of 2,4-D sprays. The optimum application timing for metsulfuron was during the late-flower growth and fruiting stages. Fall-applied metsulfuron at 0.035 kg/ha provided 65% Wyoming big sagebrush mortality compared to 27% when spring-applied. When metsulfuron was fall-applied at 0.07 kg/ha or higher, control averaged 88% following 3 annual applications. Combining metsulfuron at .0175 kg/ha plus 2,4-D at 1.1 kg/ha was comparable to or more effective than either herbicide applied alone in spring or fall. Total standing crop of grasses increased by nearly 300% after 1 or 2 growing seasons when Wyoming big sagebrush canopy cover was reduced by at least 75% following herbicide treatments.

Economic Evaluation of Wyoming Big Sagebrush (Artemisia tridentata) Control Methods

The economic feasibility of four Wyoming big sagebrush control methods: burning, spraying with 2,4-D, plowing and seeding, and rotocutting was analyzed. Perennial grass response to big sagebrush treatment was measured to estimate a treatment response function for each control method which provided the biological informational base to develop cost and benefits. Annualized present values of net additional returns for single 2,4-D and burning treatments were $1.10/ha and $1.16/ha, respectively. When big sagebrush was retreated at optimal intervals, 2,4-D and burning generated annualized net additional returns of $2.88/ha and $2.57/ha, respectively. Rotocutting was marginally feasible, and plowing was not feasible.

Changes in Rangeland Canopy Cover Seven Years After Tebuthiuron Application

Tebuthiuron was evaluated at two Wyoming locations for its effects on big sagebrush control and associated vegetation, Big sagebrush was controlled with tebuthiuron at 0.6 to 1.1 kg ai/ha. Green needlegrass, prairie junegrass, blue grama, and Douglas rabbitbrush were unaffected by tebuthiuron treatments. Western wheatgrass and downy brome increased at different study locations and were dominant grass species at the end of 7 yr.

Economic Optimum Big Sagebrush Control for Increasing Crested Wheatgrass Production

AbStnCt An approach was developed for estimating the economic optimum rate of initial overstory kill for increasing seasonal forage availability. The model was formulated using: (1) a biological production function relating understory production to initial kill percentage, (2) a derived demand function for seasonal forage value, and (3) a cost of overstory kill function for each control method. The specific optimum solution will vary irith the situation; however, the general model may be applied to any ranching situation where understory forage production is constrained by undesirable overstory vegetation. The model was iilustrated using the big sagebrush-crested wheatgrass vegetation type on a Utah cow-calf-yearling operation with prescribed burning, 2,4-D spray ing, and tebuthiuron application as control methods. For the ranch analyzed, a big sagebrush kill rate between 92 and 100% is optimal depending on the derived demand and cost-of-kill functions used. Kill rates that differ from the optimum caused significant opportunity costs to be incurred. Investments in control of undesirable vegetation to increase forage production have the potential to increase red meat production, ranch profits, and other benefits to society such as reduced soil erosion. To achieve such benefits requires careful planning, implementation, and monitoring of vegetation control projects. The purpose of this study was to investigate and develop usable mathematical and tabular approaches for estimating the optimum (profit maximizing) rate of initial overstory kill for increasing seasonal forage availability on a given ranch. The focus is how the ranch should approach biological and economic decisions for the alleviation of an identified seasonal forage bottleneck in a yearlong ranch operation. The biological relationship between overstory dominance and understory production has been documented for many vegetation types (Ffolliott and Clary 1982, Bartlett and Betters 1983). The analytical approach examined in this study was illustrated using big sagebrush (Artemisia tridentata Nutt.)-crested wheatgrass (Agropyron deserrorum (Fisch. ex Link) Schult., A. crisratum (L.) Gaertn.) vegetation relationships in a Utah cow-calf-yearling operation. The rate of big sagebrush reestablishment on a specific site depends on the percentage initial kill, subsequent grazing management, ecological adaptation of sagebrush to the site, and reinvasion of sagebrush from outside the treatment area (Pechanec et al. 1965, Hull and Klomp 1966, Johnson and Payne 1968, Winward 1983). Benefits from brush reduction include improved range condition, increased forage and livestock production, ease of working cattle, increased feed for wildlife, and improved watershed conditions (McDaniel 1980). Multiple use management may dictate that not all big sagebrush be removed. However, Evans et al. (1979) examined the biological relationships and recommended

Herbicide Treatment Effects on Properties of Mountain Big Sagebrush Soils after Fourteen Years

AbstractSoil properties under stands of vegetation dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana) and grass were examined 14 yr after spraying with 2,4‐dichlorophenoxy acetic acid (2,4‐D) to control sagebrush. Changes in only a few soil chemical properties were found after conversion to grassland. Phosphorus and K were apparently redistributed from depth to the surface 5 cm of soil by grass‐dominated vegetation. Conversely, surface concentrations of N were lower under grass vegetation than under undisturbed vegetation. No changes attributable to vegetation conversion were found for total C, Na, Mg, cation exchange capacity, base saturation, pH, bulk density, or potential net N mineralization rates at any depth. In situ net N mineralization rates at a 5‐ to 15‐cm depth were measured under and between shrubs for both vegetation conditions 15 yr after spraying. Nitrogen mineralization was similar from positions between and under former shrubs in converted (grass) vegetation, whereas in the sagebrush vegetation, mineralization rates were higher under live sagebrush plants than in interspaces between plants. Undershrub net N mineralization rates were higher under shrubs in the sagebrush vegetation than under former shrubs in the grass vegetation. Essentially, control of big sagebrush, in the absence of grazing, had no effect on site fertility. The spatial distributions of the elements and of their cycling, however, have been altered.

An 18-Year Comparison of Control Methods for Wyoming Big Sagebrush in Southwestern Montana

An 18-Year Comparison of Control Methods for Wyoming Big Sagebrush in Southwestern Montana

Response to Tebuthiuron by Utah Juniper and Mountain Big Sagebrush Communities

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.

Tebuthiuron Effects on Artemisia Spp. and Associated Grasses

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was evaluated on three Wyoming soil types for control of big sagebrush (Artemisia tridentata Nutt.), silver sagebrush (Artemisia cana Pursh.), and phytotoxic effects on associated vegetation. Big sagebrush was controlled with tebuthiuron at application rates of 0.6 to 1.1 kg ai/ha, whereas silver sagebrush was not completely controlled. Prairie junegrass [Koeleria pyramidata (Cam.) Beauv.], western wheatgrass (Agropyron smithii Rydb. ♯3 AGRSM), needleandthread (Stipa comata Trin. ♯ STDCO), and green needlegrass (Stipa viritdula Trin. ♯ STOVI) were not significantly reduced with tebuthiuron up to 1.1 kg ai/ha. Blue grama (Bouteloua gracilis H.B.K. ♯ BOBGR), downy brome (Bromus tectorum L. ♯ BROTE), plains pricklypear (Opuntia polyacantha Haw. ♯ OPUPO), and broom snakeweed [Gutierrezia sarothrae (Pursh.) Britt. and Rugsby, ♯ GUESA] were tolerant to tebuthiuron at rates up to 1.1 kg ai/ha.

Long-Term Effects of Big Sagebrush Control on Vegetation and Soil Water

Herbaceous productivity of mountain big sagebrush (Artemisia tdnlataspp. vsyana)areasspnayed with 2,4-D(2,4-dichlorophenoxyacetic acid) was nearly twice that of untreated areas 10 years after spraying, while the number of sagebrush plants on treated areas was 4% of that before spraying. Soil at the Wyoming study site was a Youga loam (Argic Cryoboroll). On treated areas, soil water depletion from the surface 0.9 m of soil slightly exceeded that of untreated areas beginning the third year after spraying when herbaceous vegetation had fully responded to release from sagebrush competition. Water depletion in soil 0.9 m to 1.8 m deep was substantially less on sprayed areas compared to unsprayed areas. Seasonal water depletion in the surface 1.8 m of soil was reduced 31% the year of treatment, and about 7% between 5 and 11 years after treatment. Mathematical relationships were developed to predict the effect of sagebrush control on seasonal water depletion in the surface 1.8 m of soil, the surface 0.9 m of soil, and soil 0.9-1.8 m deep. Control of big sagebrush (Artemisia tridentata) with the herbicide, 2,4-D (2,4-dichlorophenoxyacetic acid) beginning in the late 1940's revolutionized management of sagebrush rangeland. Millions of acres have been sprayed to benefit livestock forage production. The response by vegetation to spraying has been investigated at numerous locations in years immediately after treatment, but information about reestablishment of big sagebrush on treated areas is less common. Both biotic and abiotic values are affected by spraying. Hydrologic impacts, for example, have received little attention compared to vegetative responses. The soil water regime may be altered when deeply rooting big sagebrush is replaced by shallower rooting herbaceous species and there is speculation that treatment can increase water yields in some locations. This paper focuses upon the responses by vegetation and soil water to big sagebrush control 6 to 11 years after treatment. Treatment responses in the first 5 years were previously reported (Sturges 1977). Vegetation Characteristics Spraying big sagebrush vegetation with 2,4-D commonly increases grass production 2 to 3 times above pretreatment levels, where adequate populations of herbaceous species are present (Hull et al. 1952, Hyder and Sneva 1956, Tabler 1968, Miller et al. 1980). Forb production is suppressed by spraying, but control of big sagebrush by burning does not greatly alter vegetative composition (Harniss and Murray 1973, Nimir and Payne 1978). Sagebrush control is not a permanent type conversion, but the time required for big sagebrush to return to pretreatment levels is quite variable. Harniss and Murray (1973) found that grass and forb production remained above preburn levels for 12 years after a mountain big sagebrush (A. tridentata spp. vaseyana) stand was burned, but was below preburn levels 30 years after treatment. The useful life of a spray project in Oregon exceeded 17 years (Sneva 1972). Sagebrush was a minor vegetation component in the first Author is research forester, Rocky Mountain Forest and Range Experiment Station, Laramie, Wyo. 82070. Station headquarters is in Fort Collins, in cooperation with Colorado State University. Portion's of the research were supported by the Bureau of Land Management, U.S. Department of the Interior. Manuscript received July 22, 1982. decade after treatment, but sagebrush density was similar to untreated vegetation in the fifteenth year. Big sagebrush reestablishment was investigated by Bartolome and Heady (1978) in another Oregon study. The age of sagebrush plants growing on sprayed areas indicated that treatment seldom killed all plants and that most reestablishment occurred in years immediately following treatment. Thilenius and Brown (1974) and Johnson (1969) investigated the return of big sagebrush to sprayed areas in Wyoming. Soil Water Withdrawal Characteristics Changes in the soil water regime that follow control of big sagebrush depend upon rooting depths of sagebrush and replacement herbaceous species and upon the depth of soil water recharge (Sturges 1977). Several studies indicate that water withdrawal in the surface meter of soil decreases slightly the first 2 years after sagebrush control. (Sonder and Alley 1961, Cook and Lewis 1963, Tabler 1968, Shown et al. 1972, Sturges 1977). Thereafter, water use by treated and untreated vegetation is similar. A substantial reduction in seasonal water withdrawal was detected at 2 Wyoming sites when mountain big sagebrush was sprayed. Tabler (1968) found that seasonal evapotranspiration decreased 14% the second year after spraying based on measurements to a 1.8 m soil depth, while Sturges (1977) detected differences of 19, 15, and 8% in the first, second, and fifth year after treatment, respectively. Treatment differences in seasonal water use were located almost entirely in soil 0.9 m to 1.8 m deep and accrued while vegetation was actively growing. No soil water study extended more than 5 years beyond the treatment year.

Big Sagebrush Control with Tebuthiuron

Tcbuthiuron (20% a.i. pellets) was applied h 2 years at rates of 0.25,0.5,1.0, and 2.0 kg a.i./ha on sagebrush-grass range. Mortality of big sagebrush (Artedsiu tridentata) and herbaceous yield was measured at the end of the second growing season, posttreatment. Mean mortality increased with increasing herbicide rate to 93.9% at 2 kg a.i./ha. Herbaceous yield decreased with increasing herbicide rate to a mean of 177.3 kg/ha at the 2 kg .i./ha rate contrasted to a mean of 423.9 kg/ha for the control. Big sagebrush (Artemisia tridentata) is easily controlled with 2,4-D at rates of 1.0 to 2.0 kg a.i./ ha (Hyder and Sneva 1955). Tebuthiuronl [ l-(5-tert-butyl-l,3,4-thiadiazol-2-yl)-l,3-dimethylurea] can effectively control sagebrush at rates of 2 kg a.i./ ha (Britton and Sneva 1981). The objectives of this study were to evaluate the effectiveness of tebuthiuron at rates of 2 kga.i./ ha and less in controlling big sagebrush and subsequent effects on herbaceous yield.

Karbutilate for Weed Control on Sagebrush Rangelands

Procedures were developed for simultaneous control of big sagebrush(Artemisia tridentataNutt.), green rabbitbrush [Chrysothamnus viscidiflorusVar.Viscidiflorus(Hook.) Nutt.] and downy brome(Bromus tectorumL.) with the herbicide karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1, 1-dimethylurea]. After a season of fallow, the herbicide-treated areas were seeded with perennial grasses. During the 4 yr of testing at several locations, karbutilate at 1.1 kg/ha controlled the shrubs and downy brome. A herbaceous fallow was maintained with 0.6 kg/ha of the herbicide, but 1.1 kg/ha was necessary for green rabbitbrush control. Perennial grass seedling establishment was highly variable among sites and years of testing. If germination of the seeded species occurred in the fall, stands were poor. When germination was delayed by the onset of cold weather until spring, excellent stands were obtained on plots treated 1 yr previous to seeding with 1.1 kg/ha of karbutilate. Residual herbicide activity was harmful at the time of fall seeding but herbicide residues declined by spring as shown by bioassay of soils.

Long-Term Effects of Chemical Control of Big Sagebrush

Long-Term Effects of Chemical Control of Big Sagebrush

Selective Control of Big Sagebrush Associated with Bitterbrush

The development of procedures for controlling big sagebrush (Artemisia tridentata Nutt.) by spraying with 2,4dichlorophenoxyacetic acid (2,4-D) causes concern about the possible loss of desirable forbs and shrubs on treated ranges. Blaisdell and Mueggler (1956) studied the effects of 2,4-D sprays on many forbs and shrubs associated with big sagebrush and emphasized the importance of careful range evaluations before spraying. They reported that spraying in eastern Idaho left antelope bitterbrush (Purshia tridentata (Pursh) DC.) unharmed or only slightly damaged. However, spraying with 2,4-D in eastern Oregon has caused effects on bitterbrush varying from no apparent damage to severe stand reductions. The importance of this species as fall and winter forage for cattle, sheep, and deer justifies further attention to the nature of susceptibility of bitterbrush to

Soil-Moisture Retention and Snow-Holding Capacity as Affected by the Chemical Control of Big Sagebrush (Artemisia tridentata Nutt.)

Soil-Moisture Retention and Snow-Holding Capacity as Affected by the Chemical Control of Big Sagebrush (Artemisia tridentata Nutt.)