# Presentation: 805494

## Risk Analysis for Tamarisk Control Strategies

**by**
**James F. Fairchild**
- Presented at USGS Partnership Meeting, Albuquerque, NM.Aug. 27, 2003

**U.S. Department of the Interior**
**U.S. Geological Survey**

## Columbia Environmental Research Center

## CERC Interest in Tamarisk Issue

- Ecological risk assessment of herbicides
- Development of analytical chemistry methods
- Environmental fate of herbicides
- Modeling, empirical assessment
- Efficacy trials with herbicides

## Professional Background

- Research Aquatic Ecologist, 20 years
- Non-target effects of pesticides in experimental ecosystems
- Fate of pesticides  (e.g. triclopyr, atrazine, metribuzin, etc.)
- Efficacy of herbicides for invasive plants (*Salvinia molesta*)
- Ecological risk assessment for endangered species including 		fish, invertebrates, amphibians, and plants

## Colorado River Near Moab, Utah

- Courtesy of Tom Till Gallery

## Tamarisk Control Measures

- Mechanical removal
- Prescribed fire
- Biological controls
- Herbicide application
- Combinations of approaches

## Mechanical Control

- Pros
- Can rapidly remove large numbers of trees
- Trees can be moved and piled for burning or other use
- Can be used to prepare site for re-vegetation
- Cons
- Extremely destructive of soils and wildlife habitat
- Dangerous for operators
- Can be expensive and logistically difficult

## Prescribed Fire Control

- Pros
- Emulates natural processes that can benefit native species
- Removes remaining woody debris
- Facilitates subsequent re-vegetation efforts
- Cons
- Can result in property loss
- Causes short-term habitat loss
- Public and agencies may not accept as widespread tool

## Biological Control 

- Pros
- Uses natural predator adapted to the target species
- Fewer non-target impacts on other species and habitat
- No concerns over groundwater contamination
- Cons
- Requires importation of non-native species
- Success varies depending on environmental factors
- Benefits may not be observed in acceptable time frame

## Chemical Control 

- Pros
- Can be remotely applied
- Minimal physical disturbance
- Can be conducted with volunteer efforts with training
- Cons
- Concern over water/groundwater contamination
- Causes temporary physical impacts on habitat
- Concern over non-target chemical impacts

## Framework for Risk Assessment

- Problem Formulation

- Data Gathering and Analysis

- Risk Characterization

- Discussions  Risk Assessor and Risk Manager

-      Risk Management

- Source: U.S. Environmental Protection Agency and SETAC, 1998

## Chemical Risks

- Risk to applicator
- Risk for groundwater contamination (humans)
- Risk to livestock (meat/milk contamination)
- Risk to non-target endangered plants and crops
- Non-target non-target birds and mammals
- Non-target fish toxicity

## Problem Formulation Example: Risk to Endangered Fish Species

- Use of herbicides may have non-target risks to endangered fishes.
- How sensitive are fish to the herbicide?
- Are fish likely to be exposed?
- How can risk be minimized?

## Data gathering and analysis

- Toxicity testing for species sensitivity
- How sensitive are endangered species
- Chemical efficacy testing on tamarisk
- How much is applied?
- How is it applied?
- Chemical exposure modeling
- Where does chemical go and for how long

## Multi-Species Sensitivity Distribution

## Probabilistic risk assessment: major risk

## Probabilistic risk assessment: minor risk

## Herbicides Used for Tamarisk Control

| Chemical | Rate
(Lb/acre) | Soil 
Half-life 
(d) | Water Half-life
(d) | Primary 
Fate Pathway |
| --- | --- | --- | --- | --- |
| Triclopyr salt | 2-6 | 10-46 | 1-50 | Photolysis |
| Triclopyr ester  | 2-6 | 10-46 | 1-50 | Photolysis |
| Imazapyr salt | 1.5 | 90-700 | 4-700 | Photolysis |
| Glyphosate | 1-5 | 15-140 | 35-63 | Photolysis |

## Herbicides Used for Tamarisk Control

| Chemical | Fish Toxicity
(ppm) | EEC
(ppm) | Risk 
Category
Fish |
| --- | --- | --- | --- |
| Triclopyr | 500 | 2.21 | Low |
| Triclopyr  | 1 | 2.21 | High |
| Imazapyr | >100 | 0.55 | Low |
| Glyphosate | 5-1000 | 1.84 | Low-High |

##  Chemical Application Methods

- Foliar spray
- Granular applications
- Stump cut and paint
- Basal bark injection

## Efficacy and Cost/Risk Tradeoffs

## Range of Potential Conditions

- Rangelands (livestock; commercial crops)
- Alluvial plains (groundwater concerns)
- Canyon walls (limited access)
- Riparian corridors (wildlife habitat)
- Refuge wetlands (endangered species)
- Military sites (unexploded ordinants)

## Exposure/Risk Minimization

- Conduct appropriate risk analysis
- Use of efficacious chemical
- Use of efficacious dose
- Optimization of chemical application procedures
- Amount applied
- How applied
- When applied

## Conclusions

- Tamarisk is enormous problem
- Multiple control approaches needed
- Each control method has risks and benefits
- Risks can be evaluated and minimized in a science-based framework
- Successful tamarisk removal program will involve science and the public in a partnership