Workshop Table of Contents

Saltcedar Management Workshop, June 12, 1996


Chemical Control of Saltcedar
(Tamarix ramosissima)

Nelroy E. Jackson
The Agricultural Group, Monsanto Company

Introduction

Saltcedar was introduced into the American Southwest from the Mediterranean region, and has become one of the most destructive exotic pest plants found in many riparian areas. Saltcedar has taken advantage of the man-made changes in water movement, both quantity and velocity to explode its range and has gained the attention and concern of people who live in and enjoy native habitat in the Southwest.

The initial requirement for good weed management is to identify and classify the weeds to be controlled. Saltcedar grows as a brush or tree with small leaves that exude salt. It flowers throughout the year and is a prolific seed producer. It resprouts after fire or mechanical damage. Saltcedar may grow in sparse, isolated clumps or in heavy to pure stands. Because of it's aggressive nature, saltcedar produces large amounts of biomass.

Methods of Weed Management

There are essentially 4 methods of weed management - mechanical, biological, competition, and chemical. Complete success of a weed management program depends on the integration of all methods of weed control.

Mechanical weed control, including hand-pulling, digging, use of weed eaters, axes, machetes, bulldozers, and fire, may not be the most efficient method for removal of saltcedar. Hand labor is not always available and is costly unless it is volunteered. When heavy equipment is used, soil is often disturbed with consequences such as disturbing invertebrates and other denizens of the ecosystem.

In many situations, weed control with herbicides is the most efficient and effective method of weed control for removal of exotic plants during the restoration process. The chemical method allows regeneration and/or re-population of natives or re-vegetation with native species. The use of herbicides can be specific, selective and fast.

Herbicides Available

The most critical step is the selection of an appropriate herbicide. Specific factors to be considered in a herbicide program are:- efficacy, environmental safety, soil residual activity, operator safety, application timing, and cost-effectiveness. In most situations, the initial treatment in removal of exotic plants is postemergence to the weeds. Since preemergence herbicides may control seedlings of desirable species, postemergence treatment of seedlings is preferable in situations where growth from a seed source in the soil is a problem. Herbicides with three active ingredients, totaling six trade names are being used for management of saltcedar. These are shown in Table 1.

Table 1. Trade and common names of six herbicides used for saltcedar control.

 

Trade name Common Name

Aquatic Registration
Arsenal® Imazapyr

No
Garlon® 3A Triclopyr

No
Garlon® 4 Triclopyr

No
Pathfinder® II Triclopyr

No
Rodeo® Glyphosate

Yes
Roundup® Pro Glyphosate

No

Roundup® and Rodeo® are trademarks of Monsanto Company
Arsenal® is a trademark of American Cyanamid Company
Garlon® and Pathfinder® are trademarks of DowElanco Company

Some of the factors to evaluate when choosing a herbicide are:- efficacy, application flexibility, operator exposure, cost-effectiveness, aquatic registration, toxicology, environmental fate and safety to endangered species. Additional characteristics of the herbicides are given in Table 2.

Table 2. Some characteristics of six saltcedar herbicides.

 

Herbicide Signal Word Formulation

Conc (lb. ae/gln)
Arsenal® Caution ipa-salt

2
Garlon® 3A Danger amine

3
Garlon® 4 Caution ester

4
Pathfinder® II Caution ester

0.75
Rodeo® Caution ipa-salt

4
Roundup® Pro Caution ipa-salt

3

Roundup Pro and Rodeo are efficacious, broad spectrum, postemergence herbicides that have no soil residual activity. Arsenal is a broad spectrum herbicide that has residual soil activity. Garlon 3A, Garlon 4 and Pathfinder II are effective on broadleaves, with safety to many grass species and no soil residual activity.

Modes of Action

The modes of action of the three active ingredients are given below:-

Imazapyr: Inhibits synthesis of the amino-acids - valine, leucine and iso-leucine at the ALS enzyme, leading to non-production of proteins.

Triclopyr: Auxin-type action, leading to inhibition of cell division and growth.

Glyphosate: Inhibits synthesis of the amino-acids - tryptophan, phenylalanine and tyrosine at the EPSP synthase enzyme, leading to non-production of proteins.

Methods of Application

Versatility of application methods is also important in the choice of herbicide. These choices include: broadcast and spot treatment foliar sprays by ground equipment, cut stump treatments, basal bark treatments and aerial application where appropriate. The choices for the six herbicides are summarized in Table 3 below.

Table 3. Methods of application of six saltcedar herbicides.

 

Herbicide

Foliar

Cut Stump

Basal Bark

Aerial
Arsenal®

Yes

Yes

No

Yes
Garlon®3A

Yes

Yes

Yes

No
Garlon®4

Yes

Yes

Yes

No
Pathfinder®II

No

Yes

Yes

No
Rodeo®

Yes

Yes

No

Yes
Roundup®Pro

Yes

Yes

No

Yes

Saltcedar Management with Herbicides

There are several conditions mat have to be addressed when implementing saltcedar control program. The level of infestation at the site must be considered. A control program should be based upon whether me level of infestation is sparse, in isolated clumps, light, heavy or in pure stands. A program directed at light infestations will be a failure if used for combating pure stands. A successful program will use me appropriate methods and tools for the appropriate level of infestation.

Application Rates

Recommended application rates for Rodeo and Roundup herbicides are given below:

 

Rodeo Aquatic Herbicide:

Spot Treatment: 11/2% V/V Solution plus 1/2% V/V Nonionic Surfactant
Broadcast Treatment: 71/2 PT./Acre plus 1/2%V/V Nonionic Surfactant
Cut Stump Treatment: 100% V/V Solution (Full Strength)

 

Roundup Pro Herbicide:

Spot Treatment: 2% v/v solution
Broadcast Treatment 5 QT./Acre
Cut Stump Treatment: 100% v/v Solution (Full Strength)

 

Arsenal Herbicide:

Ground: 0.75 to 1%V/V solution + 0.5% surfactant
Aerial: 1.5 to 2 QT./Acre
Cut Stump: 12 OZ. per gallon of water

 

Rodeo and Roundup Pro + Arsenal Tank Mixes:

a. Broadcast rates:

Monsanto: 2 QT. Roundup Pro or 3 PT. Rodeo + 1 PT. Arsenal /Acre (light infestations)

Monsanto: 4 QT. Roundup Pro or 6 PT. Rodeo + 2 PT. Arsenal/Acre (heavy infestations)

AmCy: 1 PT. Roundup Pro + 1 QT. Arsenal/Acre (all infestations)

b. Spot Treatment rates:

Monsanto: 1 % Roundup Pro or Rodeo + 0.25% Arsenal

AmCy: 0.5% Roundup Pro + 0.5 to 0.75% Arsenal

There is not total agreement between Monsanto and AmCy on the optimum rates of the products for use in tank mixes. All the recommended ratios work faster and better than either product alone. The enduser will have to decide on the cost per acre as well as the degree of residual control that is acceptable for a site. Roundup Pro and Rodeo treatments tend to release grasses and forbs in treated sites, whereas Arsenal at the higher end of the rate spectrum tends to control this type of vegetation the following year.

Garlon and Pathfinder II:

Foliar Treatments: 2 to 4 QT./ACRE of Garlon 4 or 3A. Dilutions with diesel are not recommended.

Modified Cut Stump Treatments: Undiluted Pathfinder II or 50% solution of Garlon 4 or 3A

Basal Bark Treatments: Undiluted Pathfinder II or a 20 - 25% solution of Garlon 4 in natural oil or diesel.

Garlon has been used successfully for many years, particularly as a basal treatment. Only triclopyr is effective in this type of application. There are no timing restrictions for application of Garlon 4 or Pathfinder ll. Garlon 3A should be applied during the growing season. Volatility of triclopyr at higher ambient temperatures could lead to undesirable effects on adjacent vegetation.

Some of the symptoms associated with glyphosate or imazapyr applications to saltcedar are yellowing and browning of the leaves, death of the meristem (growing point), "abnormal" regrowth, and multiple budding. Any of these symptoms indicate that the herbicide has had an effect upon the plant. Regrowth from stumps and roots is, unfortunately, often a symptom of a less than lethal dose of any of the herbicides.

Timing of Applications

Timing of application for optimal control is important for optimum control of saltcedar. Best results from foliar applications of Rodeo, Roundup and Arsenal are obtained when the herbicides are applied in late spring to early fall, particularly when adequate soil moisture is available for good growing conditions. This is shown in the accompanying chart. [Note: The chart is not included in the internet version of the proceedings.]

Post-Spray Management

After initial application of a herbicide to saltcedar, retreatment of escapes, resprouts and new germination of seedlings may be necessary. The amount of re-treatment necessary in the second and third years will be drastically reduced, provided there is no re invasion of seeds of saltcedar. Re-vegetation of the site may be done by either natural means or by planting native species.

Summary

Chemical weed control may be the optimal method for control and removal of saltcedar during the establishment of native habitat restoration projects. Roundup, Rodeo, Arsenal, Garlon 3A and 4, and Pathfinder II herbicides are the products most often chosen by managers of native habitat restoration projects because these herbicides are efficacious and cost-effective, with favorable environmental and toxicological properties.

Herbicides may be used effectively, within a defined management plan. Individual products may be applied as a foliar treatment by hand or aerially, or as a Basal Bark or Cut Stump treatment, based on label recommendations. Post-spray management includes retreatment of escapes and new growth in subsequent years, while saving desirable plants, protecting animal life, enhancing wildlife habitat and protecting water quality in riparian, estuarine and terrestrial areas.

The most desirable weed management in native habitat restoration projects may utilize a combination of chemical, mechanical, biological and competitive methods. Long-term, healthy competition from the desired species, coupled with chemical control of any re invading exotic plants may be the optimal program. In any given project, the best combination of tools should b~ selected and molded into a viable weed management program.

References

American Cyanamid Company. 1994. Label for Arsenal® herbicide.

AmericanCyanamidCompany. 1994. Technical Report #FE11315-"Herbicides proven effective in controlling saltcedar".

DowElanco Company. 1994. Label for Garlon® 3A herbicide.

DowElanco Company. 1994. Label for Garlon® 4 herbicide.

DowElanco Company. 1994. Label for Pathfinder® II herbicide.

DowElanco Company. Technical Report # 351 -12 004 - "What you should know about Pathfinder® herbicide".

DowElanco Company. Technical Report # 351 -12~05 - "What you should know about Garlon® 3A herbicide".

DowElanco Company. Technical Report # 351-12 006 - "What you should know about Garlon® 4 herbicide".

Monsanto Company. 1995. Label for Rodeo® herbicide.

Monsanto Company. 1995. Label for Roundup® Pro herbicide.

Monsanto Company. 1995. Label for Rodeo® herbicide.

Monsanto Company. 1992. Technical Report # 170-9246 - "Native Habitat Restoration - Controlling saltcedar".

Monsanto Company. 1995. Technical Report # 171 -95-21 - "Roundup Pro herbicide technical fact sheet."

Monsanto Company. 1992. Technical Report # 169-92 04 - "Technical bulletin for Rodeo herbicide".


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