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THE APPLICATION AND USE OF HERBICIDES FOR BRUSH AND WEED CONTROL

R. A. Evans, J. A. Young, and R. E. Eckert, Jr.

ABSTRACT: Use of herbicide provides effective ~~JOR BRUSH SPECIES and efficient control of brush and herbaceous weeds in the management of the sagebrush-grass By far the most abundant brush species of the ecosystem. Rabbitbrush and other root or sagebrush-grass rangelands is big sagebrush crown-sprouting shrubs are harder to control than with its three subspecies tridentata, sagebrush and require careful timing of spraying wyomingensis, and vaseyana. On specific sites or a wider spectrum of herbicides. Techniques other species of sagebrush dominate, e.g. low have been developed for control of downy brome sagebrush (A. arbuscula) and alkali sagebrush and other herbaceous weeds when seeding perennial (A. longiloba) usually occur on shallow soils, grasses for improvement of degraded sagebrush black sagebrush (A. nova) usually is associated rangelands. Weed control-seeding systems, with carbonate soils, and silver sagebrush (A. involving control of brush and herbaceous weeds cana) is found primarily on wet sites. - plus seeding of forage and browse species, have been successful in the conversion of degraded Representing seral stages after disturbances communities to stable, high-producing rangelands. and on many sites occurring as either codominant or subdominant with big sagebrush INTRODUCTION are green and gray rabbitbrush (Chrysothamnus viscidiflorus and C. nauseosus) and horsebrush The sagebrush-grass ecosystem is the largest (Tedradymia canescens). Other brush species rangeland type in the western United States. In occurring in some stands are species of Ribes, the Great Basin and Northwest subregion, which Ephedra, and Prunus. includes most of northern Nevada and parts of Utah, Idaho, Oregon, and Washington, there are HERBICIDES AND THEIR APPLICATION FOR BRUSH almost 85 million acres (35 million ha) of CONTROL sagebrush-grass rangeland (Evans and others 1981). Of these rangelands, 88 percent, almost What to Spray 75 million acres (30 million ha) are degraded to the point that they are producing 50 percent or The discovery of 2,4-D [(2,4-dichlorophenoxy) less of their forage potential (Forest Service acetic acid] as a plant growth regulator in 1972). Only 1 percent of the over 4 million 1942 began the development of synthetic acres (1.6 million ha) of sagebrush-grass hormones for weed control (Bovey 1971). rangelands in the Humboldt River Basin of northeastern Nevada are in the high forage After World War II, several scientists production class (Anonymous 1966). independently recognized the potential of 2,4-D in controlling sagebrush for the release of Low forage production on these rangelands has perennial grasses. This herbicide is currently been caused by overgrazing and other past land registered by the Environmental Protection abuses (Young and others 1979) resulting in a Agency (EPA) for use on sagebrush-grass severe depletion of native perennial grasses, a rangelands. dominance of brush, and in many instances, annual alien weed dominance in the understory. Among the first to demonstrate the effectiveness of 2,4-D for controlling big Once big sagebrush (Artemisia tridentata) becomes sagebrush were Elwell and Cox (1950), Cornelius established as the dominant species of degraded and Graham (1951), and Hull and Vaughn (1951). sagebrush-grass rangelands, it is persistent Working independently, Hyder (1953) enough to stabilize succession in these demonstrated its usefulness in eastern Oregon, communities for long periods. This tenure of and Bohmont (1954) and Hull and others (1952) dominance has not been determined, but the life demonstrated its usefulness in Wyoming. expectancy of big sagebrush may exceed 150 years Gradually, guidelines were developed to help (Ferguson 1964). Degraded rangelands dominated ensure the success of spray application. As by big sagebrush can remain static, producing the brush control program with 2,4-D became virtually no forage for decades regardless of widespread, there were a few failures, almost grazing management or even without livestock all of which can be traced to violations of the grazing. initial guidelines.

Although 2,4-D is very effective in controlling sagebrush, other brush species either occurring alone or in mixed stands with sagebrush are R. A. Evans, J. A. Young, and R. E. Eckert, Jr. more resistant to this herbicide. Effective are Range Scientists at the Renewable Resource control of green rabbitbrush by 2,4-D requires Center, University of Nevada, Reno, Nev. careful timing of application in relation to its phenology, air temperature, and available

32 soil moisture. There are some years when 2,4-D sagebrush-grass rangelands. Big sagebrush is cannot adequately control green rabbitbrush or usually controlled by 2 lb/acre (2.2 kg/ha) of when the period of susceptibility is so short 2,4-D. With mixed stands of sagebrush and that only small areas can be treated. These green rabbitbrush control can be effective with problems have been lessened by the use of more either 3 lb/acre (3.4 kg/ha) of 2,4-D or a recently developed herbicides that translocate mixture of 0.5 lb/acre (0.6 kg/ha) of picloram better and control green rabbitbrush more and 2 lb/acre (2.2 kg/ha) of 2,4-D. effectively than 2,4-D. Also, additional research is warranted on improving efficacy of Where to Spray 2,4-D for brush control with improved application technology relative to equipment modifications; The choice of the proper site for a spray use of different total volumes of spray, and application is the most important factor in improved surfactants, additives and carriers; and ensuring the success of the herbicide treatment the use of remote sensing to more accurately as a range improvement practice. It does no predict the periods of optimum susceptibility. good to kill the brush if no perennial grasses are available to take advantage of the released The most effective and widely tested of the environmental potential (Alley 1956). Hyder alternative herbicides has been picloram and Sneva (1965) developed the.rule-of-thumb (4-amino-3,5,6-trichloropicolinic acid). that only if one could step from plant to plant Relatively low rates of picloram have been shown of desirable perennial grass species, would to be extremely effective for control of green there be enough perennials to permit a forage rabbitbrush (Tueller and Evans 1969; Cook and response and to prevent the invasion of annual others 1965). Picloram does not control big grasses or other desirable species. sagebrush at these rates, so 2,4-D must be applied with the picloram for control of both The best sites to spray are old, even aged, species. Picloram has not been marketed as a stands of big sagebrush with many mature mixture with low-volatile esters (l.v.e.) of plants. Errors can be made by spraying sites 2,4-D. Tank mixtures of potassium salts of of low sagebrush and expecting them to be as picloram and l.v.e. of 2,4-D have been effective productive as big sagebrush sites. Eckert and in aerial applications to mixed stands of green others (1972) reported an average increase of rabbitbrush and big sagebrush (Evans and Young 436 lb/acre (488 kg/ha) total forage production 1975). at nine locations in northern Nevada with low sagebrush control of 96 to 100 percent. Errors Picloram has been registered for application can be made by spraying sites with desirable either alone or in tank mixtures with 2,4-D for species such as bitterbrush (Purshia control of rabbitbrush and other brush species on tridentata), which can lead to confrontations rangelands by EPA with a Special Local Needs between range managers and wildlife biologists. Label for Idaho, Nevada, Oregon, Utah, and These confrontations are unnecessary, because Washington.·· A Supplemental Use Label has been careful selection of sites to be sprayed can issued for control of weed and brush species, prevent them. Also, by application of timing including rabbitbrush, in Wyoming. techniques developed by Hyder and Sneva (1962), big sagebrush can usually be removed from a Tebuthiuron (N-[5-(1,1-yimethylethyl)-1,3, site without killing the desirable bitterbrush. 4-thiadiazol-2yl] -N, N -dimethylurea] and dicamba (3,6-dichloro-~nisic acid) are both Errors were also made in choosing sites with registered for brush control on rangelands by EPA large populations of green or gray rabbitbrush but there are very few publications verifying or horsebrush. These root-sprouting species their efficacy in the sagebrush-grass rangelands. are relatively difficult to control, and Britton and Sneva (1981) indicated that improper application of 2,4-D to sites with frequencies of big sagebrush and low sagebrush these species often released them from were severely reduced by 1.8 lb/acre (2 kg/ha) of competition by big sagebrush (Robertson and tebuthiuron (20 percent a.i. pellets) and green Cords 1957). rabbitbrush was virtually eliminated by 3.6 lb/acre (4 kg/ha). At these rates, accompanying When to Spray perennial grasses were also damaged. Big sagebrush is most susceptible to 2,4-D when Further studies in Oregon with tebuthiuron at it is growing rapidly in the spring. Because lower rates indicate control of big sagebrush of big sagebrush has persistent leaves, its 80 percent with 0.87 lb/acre (1 kg/ha), 58 phenology is difficult to measure. Hyder percent with 0.75 lb/acre (0.8 kg/ha), and 35 (1954) used the phenology of the native percent with 0.5 lb/acre (0.6 kg{?a) a.i. of the perennial grass, Sandberg bluegrass (Poa 20 percent pellets, respectively-. No sandbergii) to estimate the correct time for significant damage was seen on perennial grasses applying herbicides. He concluded that the when tebuthiuron was applied at these rates. At correct time for spraying in eastern Oregon this time, 2,4-D is the principal and the most extended from the heading of Sandberg bluegrass practical herbicide for brush control on until one-half of the green color was gone. Measurements of soil moisture were determined to be important in estimating the correct time for herbicide application, which generally was 1 Miller, R. Burns, OR: Data on file at USDA the month of May. However, on shallow soils or Agriculture Research Service. south slopes, the correct application time may

33 be earlier and of much shorter duration and in Original recommendations called for the butyl wet years it may be later and of much longer or isopropyl ester to be applied at 1.0 to 1.5 duration. lb a.i./acre (1.1 to 1.7 kg a.i./acre) with sufficient water for application at 5 gal/acre In Wyoming a more reliable way of estimating the (47 1/ha). Low-volatile esters were correct timing of herbicide application was from recommended where big sagebrush was hard to the phenology of big sagebrush itself rather than control. Some range managers preferred diesel reliance on that of other species (H. P. Alley, oil to water as a carrier, but the increase in personal communication). efficiency of weed control seldom justified the increase in cost. As was previously noted, species of rabbitbrush are more difficult to control with 2,4-D than big In an assessment of spraying for control of big sagebrush. Hyder and others (1958, 1962) sagebrush in the Vale project in southeastern determined that application must be carefully Oregon, Heady and Bartolome (1977) concluded timed for adequate control of rabbitbrush. The that no clear-cut advantage was gained by the current annual growth of the shoots must reach 3 use of oil as a carrier. However, many land inches (7.6 em) and soil moisture must be managers and some scientists (H. P: Alley, available if the herbicide is to be effective. personal communication) strongly believe that The length of time that green rabbitbrush is oil is a better carrier than water for applying susceptible to 2,4-D varies greatly among years 2,4-D to big sagebrush. and location. The period of susceptibility may equal that of big sagebrush or it may not occur Errors made in spraying for big sagebrush at all. control include improper mixing of the herbicide and carrier, flying too high or fast, In mixed stands of big sagebrush and rabbitbrush, and improper marking of sites to be sprayed herbicide application should be timed with the during herbicide application (Pechanec and phenology of rabbitbrush because of its usually others 1965). Such errors are probably less shorter period of susceptibility. important than errors in the timing of spraying (F. A. Sneva, personal communication). Prediction of the optimum date for application of 2,4-D to green rabbitbrush is essential because To spray small areas or places remote form herbicide-mixing facilities, aircraft, and agricultural areas where aerial applicators may flagging crews must be prepared in advance if be difficult to obtain, a ground sprayer for they are to be ready for the application at the herbicide application may be more practical often remote sites by the chosen date. than aerial application. Young and others (1979) have modified readily available Prediction is complicated by the phenology power-ground sprayers to permit their use on pattern of growth for green rabbitbrush, in which sagebrush rangelands. 40 percent of tlie current year's growth can occur within 2 weeks before the optimum application TENURE OF GRASS DOMINANCE AFTER RELEASE date (Young and Evans 1974b). Prediction is further complicated by the interaction of age and How long do perennial grasses remain dominant competition on the growth rate and phenology of after release from shrub competition? This is green rabbitbrush. Young stands grow faster than one of the most perplexing questions involved old stands that are competing with big sagebrush in economic evaluations of the use of plants. herbicides for brush control in sagebrush/grasslands (Johnson 1969; Sneva Color infrared photography can be used to predict 1972). Some grass communities are reinvaded by the optimum spray date for green rabbitbrush shrubs almost immediately after brush control. (Evans and others 1973; Young and others 1976). Very few stands have remained virtually This method has the advantage of enabling the shrubfree for years (Weldon and others 1958). collection of large, statistically precise Sneva (1972) believed that sagebrush control in samples from remote areas in a very short time. the Great Basin lasts longer than sagebrush A single trained interpreter can predict the control from similar treatments in Wyoming optimum application date from photographs and because of the intense summer drought in the return a recommendation within 24 hours. Great Basin, which limits seedling establishment of shrubs. Other scientists How to Spray believe that Johnson's (1969) estimate of the useful life of sprayed areas in Wyoming was too Aerial applications of 2,4-D are the most short, because the stands he studied did not practical to control big sagebrush on large initially have complete shrub control (H. P. areas. Prevailing recommendations today are to Alley, personal communication). spray 2 lb/acre (2.2 kg/ha) of low volatile esters of 2,4-D in 5 gal/acre (47 1/ha) of water Competition between big sagebrush and perennial for big sagebrush control. When green grasses has been studied for many years rabbitbrush occurs in the stand it is necessary (Robertson and Pearse 1945; Blaisdell 1948; to increase the rate of 2,4-D to 3 lb/acre (3.3 Cook 1958). Working with crested wheatgrass kg/ha) for acceptable control. (Agropyron desertorum) and Wyoming big sagebrush (!. tridentata subsp. wyomingensis), Rittenhouse and Sneva (1976) reported that perennial grass production declined 3.3 to 5.7

34 , percent for every 1 percent increase in brush If in the annual community being treated with crown cover. paraquat contained tumble mustard (Sisymbrium altissimum) 2,4-D at 0.5 lb/acre (0.6 kg/ha) On public lands, the maintenance of mixed stands was added for control of this species. of perennial grasses, forbs, and shrubs is a goal Paraquat, a contact herbicide, must be applied of multiple-use management, even though maximum after the downy brome has emerged. In most of forage production may result only with minimum the sagebrush/grasslands this makes spring density of big sagebrush. In keeping with this seeding necessary. goal, the guidelines of most public land management agencies specify that spraying of big Unde~ the environmental conditions of the sagebrush is to provide only incomplete control sagebrush/grasslands, it is difficult to of shrubs. The goal is desirable, but the consistently control downy brome with aerially methodology for achieving it may be faulty. applied paraquat even though ground Studies by Young and Evans (1974a) have shown applications are always effective. The that partial control of shrubs (15 to 65 percent) addition of proper surfactants enhances the can lead to dramatic increases in shrub density effectiveness of ground applications of through increased seed production and seedling paraquat (Evans and Eckert 1965): establishment. Almost complete control of shrubs (85 to 98 percent) on some areas with no control Atrazine Fallow on adjacent ones may be a more effective alternative. The dynamics of both partial After evaluating large numbers of soil-active control of shrubs in relation to perennial grass herbicides, Evans and others (1969) determined density and the post-treatment invasion of shrubs that atrazine [2-chloro-4-(ethylamino)-6- into grass-dominated communities are aspects of (isopropylamino)-s-triazine] was the best sagebrush/grasslands ecology that merit further candidate for creating herbicidal fallows. The study. characteristics evaluated were spectrum of weed control, consistency of performance among years HERBACEOUS WEEDS and amount of herbicide residue 1 year after application. Within the sagebrush/grasslands, control of herbaceous weeds is predominantly the control of The atrazine-fallow technique was developed alien annuals to allow the establishment of (Eckert and Evans 1967) and tested extensively seedlings of desirable perennials. The secondary (Eckert and others 1974). Atrazine is successional role of native herbaceous species registered by EPA for specific uses on has been almost entirely preempted by downy brome sagebrush rangelands. The atrazine is applied (Bromus tectorum) and associated alien species at 1.0 lb/acre (1.1 kg/ha) in the fall and a (Piemeisel 1938). fallow is created during the next growing season. The area is seeded to wheatgrasses Sites dominated by downy brome are largely closed years after the herbicide is applied. The to the establishment of perennial grass seedlings amount of herbicide residue that is present at (Robertson and Pearse 1945). Attempts to the time of seeding is critical in the success introduce wheatgrass in downy brome sites by of seedling establishment (Eckert and others seeding generally have failed unless the site was 1972; Eckert 1974). Seedling success is first fallowed by mechanical methods (Hull and enhanced by seeding wheatgrasses in the bottom Holmgren 1964). of furrows made with a modified rangeland drill (Asher and Eckert 1973). The furrow provides a The alien annual grass medusahead (Taeniatherum favorable microenvironment for seedling asperum) has invaded portions of Oregon, establishment (Evans and others 1970) and California, Washington, and Idaho (Young and removes herbicide residues on the soil surface Evans 1970). Medusahead invasion in the to the area between the furrows. sagebrush/grasslands is largely restricted to low sagebrush sites (Young and Evans 1971). The atrazine-fallow technique works equally well on medusahead and downy brome (Young and Paraquat Evans 1971).

The herbicide paraquat (1,1'-dimethyl-4, \\TEED-CONTROL SYSTEMS 4'-bipyridinium ion) was first used for downy brome control on sites to be reseeded because of The development of techniques has been its relatively unique characteristic of being described for controlling excessively dense deactivated upon absorption to the soil. This stands of big sagebrush and releasing native characteristic permits the spraying of paraquat perennial grasses. It has been stressed that at 0.5 to 1.0 lb/acre (0.6 to 1.1 kg/ha) and the sites without enough perennial grasses to immediate seeding of wheatgrasses (Evans and preempt the environmental potential released by others 1967). Paraquat is registered by EPA for killing the brush should not be sprayed. If specific use on sagebrush rangelands. It is a such degraded big sagebrush sites are not restricted-use herbicide because of its high invaded by downy brome, the brush can be mammalian toxicity. Proper care must be sprayed and a heavy-duty rangeland drill used exercised in its use. to seed in the standing dead brush (Kay and Street 1961). For most sites, the use of a rangeland drill modified to make furrows

35 enhances seedling establishment (Asher and Eckert Asher, J. E.; Eckert, R. E., Jr. Development, 1973). testing, and evaluation of a deep furrow drill-arm assemble for the rangeland drill. For big sagebrush communities in which the J. Range Manage. 26: 377-379; 1973. perennial grasses are gone and downy brome has invaded the shrub understory, it is possible to Blaisdell, J. P. Competition between sagebrush combine in sequence 2,4-D and atrazine-fallow seedlings and seeded grasses. Ecology 30: treatments into a weed-control system (Evans and 512-519; 1949. Young 1977). The system can be used by (a) applying the atrazine in the fall and the 2,4-D Bohmont, D. W. Chemical control of big the next spring, (b) applying the 2,4-D in the sagebrush. Mimeo. Circ. 39. Wyoming spring and the atrazine the next fall, or (c) Agriculture Experiment Station; 1954. 3 p. applying a mixture of both herbicides in the spring at the optimum date for brush control. Bovey, R. W. Hormone-like herbicides in weed control. Econ. Bot. 25: 385-400; 1971. Atrazine fallows make excellent seedbeds for transplanting seedlings of desirable browse Britton, C. M.; Sneva, F. A. Effects of species (Christensen and others 1974). Shrub tebuthiuron on western juniper. J. Range transplanting can also be adapted to weed-control Manage. 34: 30-32; 1981. systems in which atrazine and 2,4-D are used (Evans and Young 1977). Christensen, M. D.; Young, J. A.; Evans, R. A. Control of annual grasses and revegetation in MANAGEMENT ponderosa pine woodlands. J. Range Manage. 27: 143-145; 1974. From the very beginning of research on control of big sagebrush, range scientists have stressed Cook, C. W. Sagebrush eradication and broadcast that probably more programs failed for lack of seeding. Logan, UT: Bull. 404. Utah post-treatment management than for any other Agriculture Experiment Station. 1958. 23 p. reason except the choice of sites with too few perennial grasses. Cook, C. W.; Leonard, P. D.; Bonham, C. D. Rabbitbrush competition and control on Utah Ideally, areas treated with 2,4-D for control of rangelands. Bull. 454. Logan: Agriculture big sagebrush should be allowed to rest the Experiment Station, Utah State University; season after spraying and should not be grazed 1965. 28 p. the next season until after the seeds of the perennial grasses are ripe. Subsequently, proper Cornelius, D. R.; Graham, G. A. Selective grazing management must be practiced to maintain herbicides for improving California forests the perennial grass stand. Such management and ranges. J. Range Manage. 4: 95-100; 1951. requires fencing and water-source development. All too often the sprayed areas have been the Eckert, R. E., Jr. Atrazine residue and only productive areas in grazing allotments, and seedling establishment in furrows. J. Range the lack of post-treatment management has allowed Manage. 27: 55-56; 1974. overutilization of the perennial grasses that were released from competition when the brush was Eckert, R. E., Jr.; Asher, J. E.; Christensen, killed. M.D.; Evans, R. A. Evaluation of the atrazine-fallow technique for weed control In degraded rangelands where big sagebrush is and seedling establishment. J. Range Manage. sprayed and perennial grasses are seeded or 27: 288-292; 1974. browse species are transplanted into the dead brush, grazing must be delayed for 1 to 3 years Eckert, R. E., Jr.; Bruner, A. D.; Klomp, G. J. to protect the seedlings and young plants from Response of understory species following damage until they become established. herbicidal control of low sagebrush. J. Range Manage. 25: 280-285; 1972. PUBLICATIONS CITED Eckert, R. E., Jr.; Evans, R. A. A Alley, H. P. Chemical control of big sagebrush chemical-fallow technique for control of and its effect upon production and utilization downy brome and establishment of perennial of native grass species. Weeds 4: 164-173; grasses on rangeland. J. Range Manage. 20: 1956. 35-41; 1967.

Anonymous. Water and related land resources, Eckert, R. E., Jr.; Klomp, G. J.; Evans, R. A.; Humboldt River Basin, Nevada - Basinwide Young, J. A. Establishment of perennial Report. Report No 12. Reno, NV: Economic wheatgrasses in relation to atrazine residue Research Service, Forest Service, Soil in the seedbed. J. Range Manage. 25: 219-224; Conservation Service, and Max C. Fleischmann 1972. College of Agriculture, University of Nevada; 1966. 120 p. and maps. Elwell, H. M.; Cox, M. B. New methods of brush control for more grass. J. Range Manage. 3: 46-51; 1950.

36 Evans, R. A.; Eckert, R. E., Jr. Hyder, D. N. Controlling big sagebrush with Paraquat-surfactant combinations for control of growth regulators. J. Range Manage. 6: downy brome. Weed Sci. 13: 150-151; 1965. 109-116; 1953.

Evans, R. A.; Eckert, R. E., Jr.; Kay, B. L. Hyder, D. N. Spray --- to control big Wheatgrass establishment with paraquat and sagebrush. Bull. 538. Corvallis, OR: tillage on downy brome ranges. Weed Sci. 15: Agriculture Experiment Station, Oregon State 50-55; 1967. College; 1954. 12 p.

Evans, R. A.; Eckert, R. E., Jr.; Kay, B. L.; Hyder, D. N.; Sneva, F. A. Herbage response to Young, J. A. Downy brome control by soil-active sagebrush spraying. J. Range Manage. 9: herbicides for revegetation on rangelands. Weed 34-38; 1956. Sci. 17: 166-169; 1969. Hyder, D. N.; Sneva, F. A. Selective control of Evans, R. A.; Herbel, C. H.; Barnes, R. F.; big sagebrush associated with bitterbrush. J. Carlson, G. E. SEA-AR Range Research Assessment Range Manage. 15: 211-215; 1962. - Great Basin and Northwest Subregion. U.S. Department of Agriculture, Agriculture Research Hyder, D. N.; Sneva, F. A.; Chilcote, D. 0.; Service; 1981. 49 p. Furtick, W. R. Susceptibility of big sagebrush and green rabbitbrush with emphasis Evans, R. A.; Holbo, H. R.; Eckert, R. E., Jr.; upon simultaneous control of big sagebrush. Young, J. A. Functional environment of downy Weeds 6: 289-297; 1958. brome communities in relation to weed control and revegetation. Weed Sci. 18: 154-162; 1970. Hyder, D. N.; Sneva, F. A.; Freed, V. H. Evans, R. A.; Young, J. A. Aerial application of Susceptibility of big sagebrush and green 2,4-D plus picloram for green rabbitbrush rabbitbrush to 2,4-D as related to certain control. J. Range Manage. 28: 315-318; 1975. environmental, phenological, and physiological conditions. Weeds 10: 288-295; Evans, R. A.; Young, J. A. Weed 1962. control-revegetation systems for big sagebrush-downy brome rangelands. J. Range Johnson, W. M. Life expectancy of sagebrush Manage. 30: 331-336; 1977. control in central Wyoming. J. Range Manage. 22: 177-182; 1969. Evans, R. A.; Young, J. A.; Tueller, P. T. Current approaches to rabbitbrush control with Kay, B. L.; Street, J. E. Drilling wheatgrass herbicides. Down to Earth. 20: 350-356; 1973. into sprayed sagebrush in northeastern California. J. Range Manage. 14: 271-273; Ferguson, C. W. Annual rings in big sagebrush 1961. Artemisia tridentata. Papers of the Lab of Treerings, Tucson, AZ: Research University of Pechanec, J. R.; Plummer, A. P.; Robertson, J. Arizona Press; 1964. 95 p. H.; Hull, A. C., Jr. Sagebrush control on rangelands. Agric. Handb. 217. Washington, Forest Service. The nation's range resources - a DC: U. S. Department of Agriculture. 1965. 40 forest-range environmental study. U.S. p. Department of Agriculture Forest Resource Report 19; 1972. 147 p. Piemeisel, R. A. Changes in weedy plant cover on cleared sagebrush land and their probable Heady, H. F.; Bartolome, J. The Vale rangeland cause. Circ. 229. U.S. Department of rehabilitation program: The desert repaired in Agriculture; 1938. 44 p. southeastern Oregon. Res. Bull PNW-70. Portland, OR: U.S. Department of Agriculture, Rittenhouse, L. R.; Sneva, F. A. Expressing the Forest Service, Pacific Northwest Forest and competitive relation between Wyoming big Range Experiment Station; 1977. 139 p. sagebrush and crested wheatgrass. J. Range Manage. 29: 326-327; 1976. Hull, A. C., Jr.; Holmgren, R. C. Seeding southern Idaho rangelands. Res. Pap. INT-10. Robertson, J. H.; Cords, H. P. Survival of Ogden, UT: U.S. Department of Agriculture, rabbitbrush, Chrysothamnus spp., following Forest Service, Intermountain Forest and Range chemical burning, and mechanical treatments. Experiment Station; 1964. 31 p. J. Range Manage. 10: 83-89; 1957.

Hull, A. C., Jr.; Kissinger, N. A., Jr.; Vaughn, Robertson, J. H.; Pearse, C. F. Range reseeding W. T. Chemical control of big sagebrush in and the closed community. Northwest Sci. 19: Wyoming. J. Range Manage. 5: 398-402; 1952. 58-66; 1945.

Hull, A. C., Jr.; Vaughn, W. T. Controlling big Sneva, F. A. Grazing return following sagebrush sagebrush with 2,4-D and other chemicals. J. control in eastern Oregon, J. Range Manage. Range Manage. 4: 158-164; 1951. 25: 174-178; 1972.

37 Tueller, P. T.; Evans, R. A. Control of green rabbitbrush and big sagebrush with 2,4-D and picloram. Weed Sci. 17: 233-235; 1969.

Weldon, L. W.; Bbhmont, D. W.; Alley, H. P. Reestablishment of sagebrush following chemical control. Weeds 6: 298-303; 1958.

Young, J. A.; Eckert, R. A., Jr.; Evans, R. A. Historical perspectives regarding the sagebrush ecosystem. In: The Sagebrush Ecosystem: A Symposium; proceedings; 1978 April; Logan, UT. Logan UT: Utah State University; 1979: 1-13.

Young, J. A.; Evans, R. A. Invasion of medusahead into the Great Basin. Weed Sci. 18: 89-97; 1970.

Young, J. A.; Evans, R. A. Medusahead invasion as influenced by herbicides and grazing on low sagebrush sites. J. Range Manage. 24: 451-454; 1971.

Young, J. A.; Evans, R. A. Population dynamics of green rabbitbrush in disturbed big sagebrush communities, J. Range Manage. 27: 127-132; 1974a.

Young, J. A.; Evans, R. A. Phenology of Chrysothamnus viscidiflorus (Hook.) Nutt. Weed Sci. 22: 469-475; 1974b.

Young, J. A.; Evans, R. A.; Tueller, P. T. 1976. Remote sensing for optimum herbicide application date for rabbitbrush. J. Range Manage. 29: 342-344; 1976.

Young, J. A.; Roundy, B. A.; Bruner, A. D.; Evans, R. A. Ground sprayers for sagebrush rangelands. Advances in Agric. Technol. AAT-W-8. U.S. Department of Agricultural Science and Education Administration; 1979. 13 p.

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