Eight species of Tamarix were first brought to North America in the 1800s from southern Europe or the eastern Mediterranean region. Many of the species escaped cultivation and by the 1920s invaded about 4,000 ha of riparian habitat in the southwestern United States. By 1987, it was estimated to have increased to at least 600,000 ha. The success of saltcedar in the southwest can be attributed to several factors related to its growth habit, reproduction, water usage, ability to tolerate highly saline conditions, and redistribution of salt from deep in the soil profile to the soil surface. The flowers produce small, numerous, and tufted seeds that can be carried long distances by wind or water. The seeds, however, have a short period of viability, and must come in contact with suitable moisture within a few weeks of dispersal. Unlike obligate phreatophytes, such as willows and cottonwoods, saltcedar is a facultative phreatophyte and is often able to survive under conditions where groundwater is inaccessible. The high evapotranspiration rates of saltcedar can lower the water table and alter the floristic composition in heavily infested areas. Mature plants are tolerant to a variety of stress conditions, including heat, cold, drought, flooding, and high salinity. Saltcedar is not an obligate halophyte but survives in areas where groundwater concentrations of dissolved solids can average 8,000 ppm or higher. In addition, the leaves of saltcedar excrete salts that are deposited on the soil surface under the plant, inhibiting germination and growth of competing species.

During the 20th century, naturalized saltcedar has become common within major tributaries throughout the western United States. Often growing in nearly monocultural stands, saltcedar is suspected of lowering water tables, thus destroying wetlands and wildlife habitats. Management efforts have primarily relied on mechanical and cultural practices, but recent success in controlling saltcedar with imazapyr has led to wider herbicide use. Based on a number of research/extension field trials in New Mexico from 1987 to present, imazapyr applied alone or in combination with glyphosate was found to control saltcedar to levels of 90% or greater, especially when applied in August or September. For fixed-wing aircraft applications, we recommend applying imazapyr at 1.1 kg ai/ha or imazapyr plus glyphosate at 0.56 plus 0.56 kg/ha. For individual plant treatments, we recommend spraying the foliage to wet with imazapyr at 1% v/v in water, or imazapyr plus glyphosate at 0.5 plus 0.5% v/v. Herbicide activity may be reduced as saltcedar height and stem number increases.

Vegetation development bordering the Middle Rio Grande, as with most major southwestern U.S. tributaries, has historically undergone rapid and dynamic change. The introduction of saltcedar (or Tamarisk, genus Tamarix) and other exotic species into this environment within the 20th century has contributed to this process. These plants are now an integral component of the riparian vegetation mix. Manpower, logistics, and financial resources constrain the degree to which a desired riparian habitat can be restored from saltcedar thickets on the Bosque del Apache National Wildlife Refuge near Socorro, NM. Saltcedar clearing is accomplished using a combination of herbicide, burning, and mechanical control techniques costing from $750 to $1,300/ha. Soil salinity and depth to water are the principal physical features limiting revegetation efforts. Cottonwood and black willow plantings and natural regeneration after timed irrigations have produced diverse habitats that support a wide array of faunal species in areas previously occupied by homogeneous saltcedar.

Diffuse knapweed, a biennial or short-lived perennial, and spotted knapweed, a perennial, are taprooted Eurasian weeds invading rangeland in the western United States and Canada. Knapweed (Centaurea spp.) invasion is associated with reductions in biodiversity, wildlife, and livestock forage, and increased erosion. Spotted knapweed grows to about 1 m and usually has purple flowers, whereas diffuse knapweed is slightly shorter, usually with white flowers. Persistent flower bracts on diffuse knapweed bear a rigid terminal spine about 8 mm long with four or five pairs of shorter lateral spines. Bracts on spotted knapweed have dark spotted tips. Knapweed management involves a combination of containing infestations and control efforts. Hand pulling in areas with small infestations can be effective for controlling spotted and diffuse knapweeds. Picloram applied at 0.28 kg ha−1 provides control for about 3 yr. Effective long-term control of knapweeds requires periodic applications of picloram, which are only cost-effective on highly productive range sites with a residual grass understory. About 12 insect species have been released for knapweed biocontrol. Seed production has been reduced by 46% by insects feeding in the flower heads. Although insects have not reduced spotted knapweed densities, they may stress the weed and shift the competitive balance to associated species. Sheep grazing reduces the density of very young seedlings and may limit seedling recruitment into the population. In areas without a residual understory of desired plant species, revegetation of knapweed-infested rangeland is required. Components of any integrated weed management program are sustained effort, constant evaluation, and the adoption of improved strategies.

Studies were initiated in Wyoming to determine the potential of grass competition as an alternative to repetitive herbicide treatment or other cultural practices for control of Russian knapweed. An experiment was established to evaluate the effects of five grass species, including Russian wildrye cv. ‘Bozoisky.’ Picloram, applied to Russian knapweed during the first frost, reduced Russian knapweed from an average of 80.1% live canopy cover which equates to 0% control. Untreated, unseeded checks resulted in 83.9 and 81.1% control in tilled and nontilled treated plots, respectively. Grass cover increased in untreated seeded plots from an average of 11.3 and 8.2% in tilled and nontilled plots, respectively, to 65% in tilled and 66% in nontilled plots treated with clopyralid plus 2,4-D. Grass cover also increased 69.7% in tilled and 66% in nontilled plots treated with picloram. There was no significant difference between grass varieties when compared to percent Russian knapweed cover. Reductions to zero live canopy cover of Russian knapweed were obtained with a single application of picloram. Economic feasibility thresholds were obtained from four out of five varieties, including a significant difference provided by nontilled Russian wildrye treated with picloram.

Leafy spurge, a long-lived perennial, grows in many habitats, from floodplains to grasslands and mountain slopes. The plant emerges in early spring and produces showy, yellow bracts that appear in late May. The true flowers emerge in mid-June. The plant spreads by both seeds and roots and contains a white sticky latex that deters grazing by many animals. Dicamba, 2,4-D, glyphosate, and picloram have commonly been used to control leafy spurge. Picloram plus 2,4-D is frequently used for leafy spurge control in North Dakota. Ten insect species for leafy spurge biocontrol have been released in North Dakota; the most successful have been the flea beetles, Aphthona nigriscutis, A. czwalinae, and A. lacertosa. The leafy spurge gall midge (Spurgia esulae) has been most successful near wooded areas. Herbicides combined with either the leafy spurge flea beetles or gall midge have controlled leafy spurge better than either method used alone. Grazing with sheep or goats is a cost-effective method for controlling leafy spurge top growth in large infestations. Grazing combined with fall-applied picloram plus 2,4-D reduced leafy spurge density more rapidly and maintained control longer than either method used alone. Several grass species are competitive with leafy spurge including ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Pryor’ slender wheatgrass, and ‘Manska’ pubescent wheatgrass. Cultivating twice each fall after harvest for 3 yr in cropland completely controlled leafy spurge. A successful long-term management program should be designed for specific situations and should include combinations of herbicides, insects, grazing, and/or seeding competitive species.

Studies were established near Devil's Tower in Crook County, WY, to determine the potential of 11 grass species to compete with leafy spurge as an alternative to repetitive herbicide treatments. Of the 11 species, ‘Bozoisky’ Russian wildrye and ‘Luna’ pubescent wheatgrass showed the most promise for successful competition with leafy spurge and were selected for further study. Pubescent wheatgrass limited percent canopy cover of leafy spurge to 10 and 15% or less in tilled and no-till plots, respectively, 7 and 10 yr after seeding. Russian wildrye limited percent canopy cover of leafy spurge to 21% or less in tilled and 7 and 27% in the no-till plots, respectively, 7 or 10 yr after seeding. The control plots not seeded to a forage grass averaged 55% leafy spurge canopy cover.

Degradation of Great Plains rangelands can be linked to past management practices that reduced native species diversity and accelerated establishment and expansion of exotic weeds and less desirable native species. Leafy spurge is an exotic perennial weed that infests more than 1 million ha in the northern Great Plains and reduces rangeland carrying capacity by competing with desirable forages and causing infested areas to be undesirable to cattle and wildlife. Research was conducted to determine the feasibility of using herbicides to suppress leafy spurge and other resident vegetation, which facilitated planting and establishment of native tallgrasses. Four experiments were conducted where 0.28, 0.56, and 0.84 kg ai/ha imazapyr and 0.1 kg ai/ha sulfometuron were applied alone and in combination and 0.84 kg ai/ha glyphosate was applied to leafy spurge-infested range sites in fall 1991 near Ainsworth, NE, and in fall 1991, 1992, and 1993 near Ansley, NE. Research areas were burned about 200 d after herbicide application to reduce plant residue. Monoculture stands of big bluestem and switchgrass were then no-till planted in each experiment and indiangrass was no-till planted in experiments initiated at Ansley in 1992 and 1993. Yields of the planted grasses, leafy spurge, and other vegetation were measured in August at each location starting the year after planting. Imazapyr was an essential component of treatments applied before planting to facilitate establishment of highly productive stands of the tallgrasses. Generally, yields were maximized by fall treatments of 0.28 kg/ha imazapyr + 0.1 kg/ha sulfometuron for big bluestem, 0.84 kg/ha imazapyr for indiangrass, and 0.84 kg/ha imazapyr + 0.1 kg/ha sulfometuron for switchgrass. Yields of the planted grasses were frequently four times greater where these herbicides were applied compared to where glyphosate or no herbicide were applied. Leafy spurge yields were usually reduced in areas where tallgrass yields were greatest. The sequential combination of suppressing vegetation with fall-applied herbicides, burning standing dead plant residue, then no-till planting desirable native tallgrasses in the spring increased productivity of these leafy spurge-infested range sites.

Long-term control of downy brome with an integrated approach is needed in order to sustain range productivity. Studies were conducted to study the effectiveness of a combination of downy brome control practices. In two studies, glyphosate and paraquat were evaluated at various rates for up to three successive years for control of downy brome in rangeland. A third study evaluated the competitiveness of perennial cool-season grasses against downy brome in the absence of herbicides. Glyphosate, at 0.55 kg/ha, and 0.6 kg/ha paraquat provided selective downy brome control on rangeland when applications were combined with intensive grazing. Downy brome control was greater than 90% following two sequential years of 0.6 kg/ha paraquat at either the two- to eight-leaf stage or bloom stage at both study locations. At one study location, 0.55 kg/ha glyphosate provided 97% control after the first application at both growth stages. In the second study, control averaged greater than 92% following three sequential applications of glyphosate. When perennial cool-season grasses were seeded in the spring following fall tillage (no herbicides) and allowed to establish for three growing seasons, three of the five species were effective in reducing the reestablishment of downy brome. ‘Luna’ pubescent wheatgrass, ‘Hycrest’ crested wheatgrass, ‘Sodar’ streambank wheatgrass, ‘Bozoisky’ Russian wildrye, and ‘Critana’ thickspike wheatgrass controlled 100, 91, 85, 45, and 32% of the downy brome, respectively. Yields of perennial grass dry matter were 1,714, 1,596, 1,135, 900, and 792 kg/ha. Replacing noncompetitive annual grasses with competitive cool-season perennials will provide a longer term solution to a downy brome problem than the use of herbicides alone or with intensive grazing.

Purple loosestrife is an invasive, introduced plant that is usually associated with wetland, marshy, or riparian sites. It is found across the northern tier states and provinces in North America. Purple loosestrife affects the diversity of native wetland ecosystems. Infestations lead to severe wildlife habitat degradation, loss of species diversity, and displacement of wildlife-supporting native vegetation, such as cattails and bulrushes. The plant spreads effectively along waterways, and the thick, matted root system can rapidly clog irrigation ditches, resulting in decreased water flow and increased maintenance. Effective management of purple loosestrife along waterways and in riparian areas requires integrating management strategies to prevent further introductions, detecting and eradicating new infestations, and containing and controlling large-scale infestations. Management practices that aid in the control of purple loosestrife include herbicide, physical, and biological practices. Each infestation site should be individually evaluated to determine the appropriate control measure. Factors to be considered include the proximity and type of vegetation on the site, whether the water is flowing or still, and the utilization of the site and the water (domestic, irrigation, recreation, or scenic value).

Field experiments were conducted for the control of perennial pepperweed with tillage and herbicides. Perennial pepperweed infests a wide range of soils and plant communities. These studies were conducted in native hay meadows, with wild-flooding irrigation and saline/alkaline soils. Such meadows are typical of livestock ranches throughout the Intermountain Area. Tillage with periodic disking over a 2-yr period resulted in no permanent reduction in perennial pepperweed cover. Applications of 2,4-D or glyphosate eliminated perennial pepperweed seed production and greatly reduced top growth but had no permanent influence on cover of the weed by the second season following application. Applications of chlorsulfuron in the spring at flowering, in late summer after hay harvesting, or in the autumn, were effective in suppressing perennial pepperweed for 2 yr or more following application.

Field studies were conducted for 3 yr to determine weed and potato response to preemergence (PRE) and postemergence (POST) applications of rimsulfuron, metribuzin, and rimsulfuron plus metribuzin. Preemergence applications of rimsulfuron at 27 g ai/ha and POST applications at 18 g/ha controlled barnyardgrass, redroot pigweed, and wild buckwheat. Common lambsquarters was controlled by PRE or POST applications of metribuzin or a tank mixture of 18 g/ha rimsulfuron plus 140 g ai/ha of metribuzin. ‘Russet Burbank’ potato was relatively tolerant to all rimsulfuron, metribuzin, and rimsulfuron plus metribuzin applications, and potato yield was not reduced compared to the hand-weeded control.

Wetland nightshade (WNS) (Solanum tampicense Dunal) is a member of the family Solanaceae. In some texts, WNS has been referred to as Solanum houstonii Dunal, but this homonym of the 1807 S. houstonii Martyn is illegitimate according to the International Code for Botanical Nomenclature (Wunderlin et al. 1993). WNS is thought to have originated in southern Mexico, the West Indies, Guatemala, Belize (Gentry and Standley 1974), Cuba, and El Salvador (Standley 1924). It was first reported from mainland Florida in a marsh south of Punta Gorda, Charlotte County, in 1983 (Wunderlin et al. 1993). Since that time, it has been detected in Florida in Highlands (1985), DeSoto (1991), Lee (1995), and Glades (1996) counties. Recently, WNS was rediscovered on Garden Key in the Dry Tortugas (110 km west of Key West) where it was growing in a moist seep area within the partially ruined Small Magazine in Fort Jefferson. This species has been included in the plant list of the Dry Tortugas National Park since 1974 (Reimus and Robertson 1995).

The grasses or Poaceae (Gramineae) comprise some 9,000 species grouped into about 650 taxa. Although not the largest, the family is ecologically the most dominant and economically the most important in the world (Heywood 1993).