TAMARISK (Tamarix spp.)
by Kacey Conway, Jude Sirota, and Susan Rose1

Tamarisk along the Colorado River

The above photo was taken by Norraine Harvey, Administrative Technician, on the
5th Street Bridge
overlooking the Colorado River in Grand Junction, July 2001.


Tamarisk (Tamarix spp.) is native to central Asia. In the late 1800s, eight tamarisk species were brought to the United States for erosion control and to be used as ornamentals, windbreaks and shade trees. In this environment, tamarisk has no natural enemies such as insects or diseases to keep its population in check. This has allowed it to spread unchecked along western waterways.

Three of these imported species, Tamarix ramosissima, T. chinensis, and T. parviflora, pose a significant threat to western ecosystems and have become a serious problem in fragile riparian areas. Dense thickets of these exotics can be seen in wetlands areas throughout the western states. Along the Colorado River, tamarisk can be seen choking the river banks from Western Colorado to Southern California.

Tamarisk is extremely adaptable and has aggressive survival characteristics that make it particularly insidious in the arid western United States. It establishes easily in areas where surface water or ground water is available, which makes it especially threatening to desert springs, oases and waterholes. Tamarisk threatens wildlife in these areas by soaking up the available water, changing water quality, driving out native grasses, trees, and shrubs, and blocking access to water by its dense growth.

Every year a mature tamarisk produces up to 500,000 seeds which are disbursed by wind and water. Plants grow rapidly, maturing from a seedling in just one year. The roots of tamarisk can grow to depths of at least ninety feet and draw water up from the water table, while extensive surface roots soak up surface water. Tamarisk absorbs an enormous amount of water, losing it to the atmosphere through transpiration from leaves and stems. Along the Colorado River alone, tamarisk is estimated to absorb and transpire one half million acre-feet or 61 billion gallons of water each year. (1 acre-foot = 123,000 gallons)

Tamarisk, also called salt cedar, uses the salty soils to its advantage. It absorbs salt through its root system which accumulates in salt glands in the leaves. When the leaves drop in fall the salts are deposited in the surrounding soil, preventing growth of other vegetation. Native riparian plants such as cottonwood and willow cannot compete. Cottonwood will not tolerate salt concentrations of more than 1,500 ppm, but salts in soils around tamarisk shrubs measure as high as 41,000 ppm which is higher than sea water.

Fire favors tamarisk. The dense thickets are hot and dry so fire occurs frequently and spreads rapidly. Tamarisk's extensive and deep root structure is largely unharmed by fire, allowing it to recover more quickly than native plants and fill in the burned area. For this reason, fire is not recommended as a control measure.

Control Methods:

Because Tamarisk does not naturally occur in the Americas, it has no natural enemies and is extremely difficult to control. Control efforts have included mechanical methods such as ripping, bulldozing and fire; chemical control with herbicides; and biological control. Experience has shown that the plant will keep coming back unless the root system is killed or removed completely. As with other weed control efforts, an integrated approach using a combination of methods is most effective.

Mechanical Control

Sprouts from remaining roots will appear for 1-3 years after bulldozing, ripping or cutting down tamarisk. Treat the sprouts using a backpack sprayer or hand sprayer with a 20% solution of 1 part Garlon4 ® (triclopyr) to 4 parts vegetable crop oil (MSO or JLB+) or with a pre-mixed herbicide called Pathfinder ® .

Chemical Control

Two pesticides are effective for killing tamarisk: imazapyr (the active ingredient in Arsenal ® ) and triclopyr (the active ingredient in Garlon 4 ® and Pathfinder ® ).

Foliar: Apply Arsenal ® , in a 1% solution (1.3 oz/gal of water or 5.5 oz/ 4-gal backpack sprayer) to wet the foliage during the summer months between July and September. This method is best for small trees where full coverage with the herbicide is possible. Foliar applications can be applied by a licensed professional to large infestations using an aircraft or helicopter.

Cut stump: This is the treatment of choice for killing tamarisk after cutting it down in areas where desirable vegetation is growing. The cut stump treatment can be used any time during the year, but preferably when there are no leaves on the trees (for easier removal of the cuttings) and the temperature is above 55 degrees F (for the herbicide to be effective.) Use Garlon4 ® with a vegetable crop oil (JLB+ or MSO) in a 25% solution (1 part Garlon4 ® to 3 parts oil). The mixture should be sprayed or painted on the cut surface of the stump immediately (within 10 - 15 minutes) after the shrub is cut down. This method is especially effective on shrubs or trees with a diameter of 2 inches or more or those with rough, gnarly bark.

Basal bark: For young sprouts or seedlings with smooth bark and diameters of less than two inches, spray the basal 12-18 inches of the plant with a 20% solution of Garlon4 ® in crop oil (1 part Garlon4 ® to 4 parts oil). Pathfinder ® herbicide is pre-mixed and can be directly sprayed on young seedlings and re-sprouts.

For any chemical treatments, always read the product label and follow the directions on the label for application, precautions and appropriate personal protective clothing and equipment.

Biological control: A leaf feeding beetle (Diorhabda elongata) that defoliates tamarisk has been introduced from Central Asia. Releases of this insect are in the experimental stage at this time. Extensive testing has shown that the beetle feeds and reproduces only on tamarisk. Preliminary research indicates that the tamarisk dies after 3 years of defoliation by this insect. A second tamarisk feeding insect, a mealy bug (Trabutina mannipara) is being investigated but has not been released at this time.

Need for Monitoring

Because the seed source in the west is so great, tamarisk can easily re-invade a treated area. Therefore, the area will need to be monitored every year for new seedlings that can be easily treated with the basal spray technique.


1 Kacey Conway, former Colorado Master Gardener; Jude Sirota, Mesa County Pest and Weed Inspector; Susan Rose, Horticulture Technician, Colorado State University Cooperative Extension


References:

1. Everitt, B.L. 1980. Ecology of Saltcedar - a Plea for Research. Environmental Geology, Number 3, pp. 77-84.

2. Carpenter, Alan T. 1998. The Nature Conservancy Element Stewardship
Abstract for Tamarix ramosissima, T. pentandra, T. chinensis, T. parviflora.

3. DeLoach, C.J, Carruthers, R.I., Lovich, J.E., Dudley, T.L., and Smith, S.D. 1999.
Ecological Interactions in the Biological Control of Saltcedar (Tamarix spp.) in the United States: Toward a New Understanding. In Proceedings of the X International Symposium on Biological Control of Weeds. July 4-14, 1999. Montana State University, Bozeman, Montana.

4. Effects of Biological Control of Saltcedar (Tamarix ramosissima) on Endangered Species: Biological Assessment. (Draft). 1997. Prepared by DeLoach, C.J., Gould, Julie, Tracy, James. United States Department of Agriculture. Agricultural Research Service, Grassland Soil and Water Research Laboratory. Temple, Tx.

5. Zimmerman, Julie A. 1997. Ecology and Distribution of Tamarix chinensis Lour. and T. parviflora D.C., Tamariaceae. Southwest Exotic Plant Mapping Program, USGS.

6. Westbrooks, Ph.D. 1998. Invasive Plants: Changing the Landscape of America. Federal Interagency Committee for the Management of Noxious and Exotic Weeds. Washington, D.C.

7. Deuser, C. 1996. Decision criteria for developing saltcedar management programs. In the Proceedings of the Saltcedar Management Workshop, pp. 37-38. Cooperative Extension Service, University of California, Davis.

8. DeGouvenain, R. 1996. Origin, history and current range of saltcedar in the U.S. In the Proceedings of the Saltcedar Management Workshop, Pp. 1-3. Cooperative Extension Service, University of California, Davis.


Placed on the Internet 7/24/2003

Comments on this page should be addressed to Dr. Curtis E. Swift, Area Extension Agent, Horticulture
Colorado State Cooperative Extension
2775 US Hwy 50, Grand Junction, CO. 81503
voice: 970-244-1834
fax: 970-244-1700