BOARD01713

• Board Meeting Date: 7/28/2003
• Description: CF Section - Tamarisk Control and Eradication Update
• Board Meetings - Doc Type: Memo

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Impact of Tamarisk Infestation on the
Water Resources of Colorado
May 30. 2003

Comparison of Tamarisk Control Techniques

All of the following tamarisk control techniques are appropriate, but each must be selected based
on local conditions; i.e., Integrated Pest Management. A comparison of each control technology
is presented below.

Aerial Herbicide Spray

Effectiveness: Recent helicopter spray operations in Texas and New Mexico with foliate
herbicides have shown an effective kill rate for tamarisk of 90 percent or better in most cases.
These areas along the Pecos River are large expanses consisting of only tamarisk. Rate of
application is several hundred acres per day.

Costs: $200 to $250 per acre for contracted aerial spray application. Because of the high cost
associated with helicopter use and mobilization, the minimum acreage to realize these cost rates
is at least 1,000 acres; thus, a minimum expenditure of $200,000 to $250,000.

Impacts: Impacts are: 1) While aerial herbicide spray is extremely effective in killing tamarisk,
it also kills all other vegetation. In Colorado, most areas which are being overtaken by tamarisk
still have a mix of valuable vegetation such as cottonwood, willow, and forbs that are too
intermixed for spot aerial spraying. 2) Some areas in western Colorado and eastern Colorado are
monocultures of tamarisk and possibly could be ofsufficient size, when combined with other
nearby sites, for economic aerial application. 3) Aerial spray costs do not include the removal of
skeleton trees or revegetation. and 4) Some spot herbicide re-application will be necessary.

Applicability to Colorado: Some areas in remote canyons in western Colorado would benefit
from aerial spray technology; most of these lands are owned by BLM. Also, some areas within
the lower Arkansas River watershed may be appropriate for this method.

Mechanized Mulchill!! Equipment

Effectiveness: Recent work in the Moab, Utah area has shown that tamarisk can be effectively
controlled by using newly developed, specialized, off-the-shelf, mechanized equipment followed
by herbicide application to the cut stumps. The trees are mulched in a six- foot wide path through
tamarisk thickets at a rate of.33 to 1.0 acres per hour depending on density and terrain with a kill
rate for tamarisk at about 85 percent.

Costs: Labor, equipment depreciation, maintenance & operating costs, and herbicide costs will
range from approximately $300 to $450 for high capacity equipment (0.75 to 1.0 acres/hr.), and
$330 to $550 for medium capacity equipment (0.33 to 0.5 acres/hr.) for very dense tamarisk
growth (See Appendix B). Minimum expenditure to achieve these rates is approximately
$10,000, which should clear approximately 20 to 50 acres depending on density, terrain, and type
of equipment used.

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