Predator and Prey

# Tamarix control

June 17, 2013, 5:10 pm
 Topics: More

USA states (dark color) with identified Tamarix invasions. Source: U.S.Department of Agriculture

Tamarix control is a significant invasive species issue in the western USA, especially in the American southwest.  The woody plant genus Tamarix, also , also known by the common names tamarisk and salt cedar has many negative influences on the natural environment once this alien species becomes established including (1) increased soil salinity, (2) increased water consumption, (3) increased wildfire frequency, (4) increased frequency and intensity of flooding  and (5) altering the plant community and wildlife habitat. Tamarix is considered one of the ten most "noxious weeds" in the United States.  Scientists and conservation biologists have attempted to identify effective stragegies for eradicating Tamarix from areas that it has successfully invaded. The Tamarisk Coalition identifies five main methods of Tamarix control (1) hand cutting with herbicide application, (2) mechanical removal, (3) manual herbicide application, (4) aerial herbicide application, and (5) biological control by either goats, beetles or other herbivores.

## Manual cutting and herbicide application

Most commonly Tamarix is removed using chainsaws, after which the remaining stumps are treated with the systemic herbicide triclopyr.  This approach requires trained operators to cut the vegetation and apply the herbicide (People using this approach are sometimes referred to as tamiwhackers.) The herbicide must be applied within approximately 15 minutes of cutting. Typically, a solution of triclopyr systemic herbicide mixed in a vegetable crop oil is applied to the cut stump.  Seedlings or smaller plants with smooth bark and a stems less than one inch in diameter can be treated by spraying the bark on the bottom 12-18 inches of the stem (basal bark treatment).  Applying herbicide to both cut stumps and basal bark sprays are effective as long as the temperature exceeds 85 degrees F, at which point the triclopyr herbicide volatizes.

Hand control of Tamarix. Tamarisk Coalition

### Manual cutting and herbicide costs

Because this technique is labor intensive it can be very expensive.  Costs of removal by this method range from $1,500 per acre for lightly infested areas to$5,000 per acre for heavily infested acres.

### Manual cutting and herbicide effectiveness

The chainsaw method for the cut-stump approach is a relatively successful method of controlling tamarisk.  Approximately 15 percent regrowth requires retreatment.

### Manual cutting and herbicide applicability

This hand cutting method is appropriate for canyons, washes, irrigation ditches, and along steep river banks which are difficult to  access, and which do not necessarily comprise a large land area. Hand control is not as appropriate in areas that that are easily accessible because of its high costs.

### Manual cutting and herbicide pros and cons

(1) Manual cutting is very effective in mixed vegetation stands without killing other desirable plants. (2) This method is best used in rough terrain that is not accessible by mechanical equipment. (3) Cut biomass must either be stacked and burned, chipped, or left in piles for wildlife habitat. (4) Some spot herbicide re-application will be necessary.

## Mechanical removal

Mechanical removal involves the use of heavy equipment to physically remove the woody trees and shrubs of the Tamarix genus.

Mechanical removal of Tamarix. Tamarisk Coalition

### Mechanical removal costs

#### Insect control effectiveness

Tamarix died after three successive years of defoliation by Diorhabda elongata in tented research cages. It remains unclear whether the insects, will be effective at killing the trees or will be more effective as a control mechanism to prevent further spread. In their fourth year since release in 2001, the beetles have caused extensive defoliation of hundreds of acres of Tamarix at the Colorado, Nevada, and Wyoming research sites. Research is still progressing to determine if the insects will cause mortality to significant numbers of Tamarix trees, as defoliated trees have resprouted each year since the insects were released into the field in 2001.

### Insect control applicability

Goats will likely be most effective at controlling young stands of Tamarix that do not contain other native woody vegetation. Biological control by Diorhabda elongata is applicable to all levels of infestation, is not constrained by access conditions, and could be used in both riparian zones and upland zones.

### Insect control pros and cons

(1) Killing Tamarix may harm the endangered southwestern willow flycatcher. (2) Extensive research on Diorhabda elongata suggests a lack threat to other plant species; however there is always risk with introducing an alien species). (3) Using goats may be an effective maintenance technique after an initial kill from introduced insects. (4) Dead Tamarisk trees must be removed, and the area must be revegetated.

The removal of dead Tamarix plants is important after mechanical root crown removal, bio-control, or aerial herbicide control has been successful, becasue it reduces the potential for wildfires and facilitates revegetation. Dead trees can be removed by fire or by mechanical mulching equipment that transforms dead woody biomass into mulch.

The costs of controlled burns are approximately $50 to$150 per acre, and the costs of mechanical mulching range from $200/acre in lightly infested areas to$200/acre in moderately infested areas.

## Revegetation after Tamarisk kills

Revegetation is critical to successful long-term control of Tamarix. Costs of revegetation can include labor, seeds, plant materials, fertilizer, equipment rental, weed control and water. For narrow widths less than 50 feet, natural revegetation should to occur but may require minor to moderate costs because of soil disturbance and weed control. For broader widths (greater than 50 feet) costs will shift to the higher side because less native plant/seed will be available for reintroduction/succession. Costs range from zero when natural revegetation occurs, to $500-$1500/ acre when major revegetation is required.

## Costs and benefits of Tamarix eradication

The costs of a regionwide Tamarix eradication program include the costs of evaluation, control, revegetation, and monitoring.  The costs of a  20 year eradication and revegetation program was estimated  at $3,006/ac ($7,428/ha).  However, the estimated long-term benefits outweighed costs by $3,312 to$6,975/ac ($8,184 to$17,235/ha) or from $3.8 billion to$11.2 billion across the entire region. The resulting benefit:cost ratio for the eradication program ranges from 2.1:1 to 3.3:1.