Source: California Invasive Plant Council
URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=81&surveynumber=182.php
Invasive Plants of California's Wildland
|Scientific name||Tamarix spp.|
|Additional name information:||T. ramosissima Ledeb.; T. chinensis; T. gallica; T. parviflora|
|Closely related California natives||0|
|Closely related California non-natives:||5|
|Listed||CalEPPC List A-1,CDFA nl|
See individual species
HOW DO I RECOGNIZE IT?
Four invasive Tamarix species have been identified in California: T. ramosissima, T. chinensis, T. gallica, and T. parviflora. All four are many-branched shrubs or trees less than twenty-six feet tall with small scale-like leaves, from which comes the name saltcedar. Leaves have salt glands, and salt crystals can often be seen on leaves. Small white to deep pink flowers are densely arranged on racemes. The bark is reddish brown with smooth stems less than an inch in diameter.
Over 50 species of Tamarix were recognized by Baum (1978), and 5 are reported from California, including T. aphylla, T. chinensis, T. parviflora, and T. gallica (DiTomaso 1996). T. aphylla is not an invasive pest under most circumstances. T. ramosissima may be synonymous with T. chinensis and is sometimes incorrectly referred to as T. pentandra (Baum 1978).
|WHERE WOULD I FIND IT?||
Saltcedar is widely distributed throughout the Mojave and Colorado deserts, Owen’s Valley, the Central and South coasts, and the San Joaquin Valley. It occurs in parts of the San Francisco Bay Area and the Sacramento Valley, particularly Yolo and Solano counties. French tamarisk (T. gallica) occurs in the Central Valley, Bay Area, and Central and South coasts. Smallflower tamarisk (T. parviflora) has a similar range, but also occurs in Inyo County. Saltcedar is abundant where surface or subsurface water is available for most of the year, including stream banks, lake and pond margins, springs, canals, ditches, and some washes. Disturbed sites, including burned areas, are particularly favorable for saltcedar establishment. It survives, and even thrives, on saline soils where most native, woody, riparian plants cannot.
|WHERE DID IT COME FROM AND HOW IS IT SPREAD?||
Tamarix ramosissima is found throughout much of central Asia, from the Near East around the Caspian Sea, through western China to North Korea (Baum 1978). Although saltcedar may have been introduced into North America by the Spaniards, it did not gain recognition in the western United States until the 1800s (Robinson 1965). It was planted widely for erosion control, as a windbreak, for shade, and as an ornamental. It spreads by seed and vegetative growth. Individual plants can produce 500,000 tiny seeds per year (DiTomaso 1996), which are easily dispersed long distances by wind and water. The roots also sprout adventitiously (Kerpez and Smith 1987, Lovich et al. 1994).
|WHAT PROBLEMS DOES IT CAUSE?||
There is debate as to whether saltcedar is a consequence (Anderson 1996) or a cause (Lovich and de Gouvenain 1998) of environmental changes associated with its presence and proliferation. Regardless, the presence of saltcedar is associated with dramatic changes in geomorphology, groundwater availability, soil chemistry, fire frequency, plant community composition, and native wildlife diversity. Geomorphological impacts include trapping and stabilizing alluvial sediments, which results in narrowing of stream channels and more frequent flooding (Graf 1978). Saltcedar has been blamed for lowering water tables because of its high evapotranspiration rate, and, on a regional scale, dense saltcedar groves use far more water than native riparian plant associations (Sala et al. 1996).
Soil salinities increase as a result of inputs of salt from glands on saltcedar leaves. The dome-shaped glands consist of at least two cells embedded in the epidermal pits (Decker 1961). Increased salinity inhibits growth and germination of native riparian species (Anderson 1996). Leaf litter from drought-deciduous saltcedar increases the frequency of fire. Saltcedar is capable of resprouting vigorously following fire and, coupled with changes in soil salinity, ultimately dominates riparian plant communities (Busch 1995).
Although saltcedar provides habitat and nest sites for some wildlife (e.g., white-winged dove, Zenaida asiatica), most authors have concluded that it has little value to most native amphibians, reptiles, birds, and mammals (Lovich and de Gouvenain 1998).
|HOW DOES IT GROW AND REPRODUCE?||
Saltcedar can reproduce both vegetatively and by seed. Plants can regenerate from cuttings that fall on moist soil. Plants can flower by the end of the first year of growth (DiTomaso 1996). Studies in Arizona demonstrated that dense saltcedar stands can generate 100 seeds per square inch. Seed production occurs over a 5.5-month period, with one major and one minor peak (Warren and Turner 1975). The minute seeds of the closely related (Baum 1978) Tamarix gallica are about 0.007 inch (0.17 mm) in diameter and about 0.018 inch (0.45 mm) long. Small hairs on the apex of the seed coat facilitate dispersal by wind. Germination can occur within twenty-four hours in warm, moist soil (Merkel and Hopkins 1957).
Following germination and establishment, the primary root grows with little branching until it reaches the water table, at which point secondary root branching is profuse (Brotherson and Winkel 1986). Under favorable conditions, salt-cedar shoots reportedly grow to heights of 3-4 meters in one growing season (DiTomaso 1996). Brotherson et al. (1984) examined the relationship between stem diameter and age of saltcedar plants. Assuming that observed growth rings of stems are annual, saltcedars in Utah require 7.68 years for a 0.39 inch (1 cm) increase in stem diameter and 2.36 years in Arizona. Germination of saltcedar seeds is not greatly affected by increased salinity under experimental conditions (Shafroth et al. 1995). Saltcedar can form dense thickets.
|HOW CAN I GET RID OF IT?||
Like most invasive species, saltcedar is easily spread but difficult to eliminate. Early detection and control are critical, as saltcedar achieves dominance rapidly under favorable conditions. Efforts should be made to prevent site disturbances that contribute to its success (fire, increased soil salinity, ground disturbance, etc.). Monitoring is essential following any control effort, as some saltcedar is capable of resprouting following treatment. In addition, seedlings will continue to establish as long as saltcedar infestations persist upwind or upstream of the target area.
Manual/mechanical methods: Saltcedar is difficult to kill with mechanical methods, as it is able to resprout vigorously following cutting or burning. Root plowing and cutting are effective ways of clearing heavy infestations initially, but these methods are successful only when combined with follow-up treatment with herbicide. Seedlings and small plants can be uprooted by hand.
Prescribed burning: Fire does not kill saltcedar roots, and plants return quickly after fire if untreated by other methods. Fire is valuable primarily for thinning heavy infestations prior to follow-up application of herbicide. The consequences of fire for native plants and soil chemistry must be recognized.
Flooding: Flooding thickets for one to two years can kill most saltcedar plants in a thicket.
Insects and fungi: The USDA is currently using an international team of researchers to test thirteen species of natural enemies to control saltcedar. Of these, two have been recommended for field release in the United States, including a mealybug (Trabutina mannipara) from Israel and a leaf beetle (Diorhabda elongata) from China. Two other species are being tested in quarantine, including a psyllid (Colposcenia aliena) and a gelechiid leaf tier (Ornativalva grisea) from China. A gall midge (Psectorsema) from France has been approved for quarantine testing. Overseas testing has been completed for a foliage-feeding weevil (Coniatus tamarisci) from France, and for a pterophorid moth (Agdistis tamaricis), and a foliage-feeding weevil (Cryptocephalus sinaita subsp. moricei) from Israel (DeLoach 1997).
Grazing: Cattle have been shown to graze significant amounts of sprout growth (Gary 1960).
Heavy infestations may require stand thinning through controlled burns or mechanical removal with heavy equipment prior to treatment with herbicides. Six herbicides are commonly used to combat saltcedar, including; imazapyr, triclopyr, and glyphosate (Jackson 1996).
Several proven methods exist for removing tamarisk. Perhaps the best method is to apply an imazapyr marketed as Arsenal® to the foliage. This technique is especially effective when a tank mix is used with a glyphosate herbicide such as Rodeo® or RoundupPro®. The most frequently used method in California is to cut the shrub off near the ground and apply triclopyr, either as Garlon 4® or Garlon 3A®. This technique usually results in better than a 90 percent kill rate. Triclopyr (as Pathfinder II®) can even be applied directly to the basal bark of stems less than about four inches in diameter without cutting the stem (the bark must be wetted completely around the base of each stem).
Garlon 4®or Pathfinder II® have no timing restrictions, but Garlon 3A® should be applied during the growing season. Resprouts can be treated with foliar applications of herbicide. Foliar applications of glyphosate or imazapyr achieve best results when applied in late spring to early fall during good growing conditions. Triclopyr can be diluted with diesel or natural oils, a dilution of 3 parts water to 1 part of Garlon 4® has proven effective (Barrows 1993, Lovich et al. 1994). Application rates for these herbicides are reviewed in Jackson (1996). Only Rodeo® has an aquatic registration, making it a legal choice for application over or around water.