The concept of integrated weed management (IWM) has been around for several decades and practiced by some, but only in the last few years has this concept become popular with federal, state and local agencies. In recent years these agencies have all been involved in the "war on weeds", often entering into cooperative agreements with each other to combat the spread of noxious weeds, which know no jurisdictional boundaries.
IWM has been defined as: "The use of all suitable weed control methods to keep weed populations below the economic injury level. Methods include cultural practices, use of biological, physical, and genetic control agents, and the selective use of herbicides" (OSU Ext.8532 1993). In other words, utilizing a combination of control strategies which will hopefully result in the most effective control of the target pest species, in this case, the group of invasive plants commonly referred to as saltcedar.
The term effective control, for most agencies and organizations refers to both the economics of the control effort and the effectiveness or mortality success of control strategies used. Five control strategies have been defined that are important components to consider in your "war on weeds": cultural, biological, physical, genetic and chemical, through the selective use of herbicides (NPS, Weed Mgmt. 1990). At this time I want to describe and discuss examples of each control strategy (with the exception of genetic control agents) to ensure that everyone is aware of what is available in their saltcedar control arsenal.
The term "biological control" has historically meant the use of insects to control noxious weeds. Since most noxious weeds are exotics (not native to N. America or a specific region) most biological control agents are insects which naturally evolved with the weed species in it's native land. Usually the insect is specific to a particular weed species and usually impacts the plant through defoliation of the leaves or boring into the root/ vascular system of the plant. This type of control can occur with adult insects, their larva or both. Recently, researchers have been experimenting with the use of plant pathogens (diseases) and livestock grazing control. Biological control can be effective but usually requires long periods of quarantine by USDA, can be quite expensive and have limited effectiveness. For the past five years the USDA has been working with a mealy bug and leaf beetle from Israel as biological control agent for saltcedar. There is some concern that these insects could impact the exotic, noninvasive species of commonly referred to as Athel. This species has been imported, and planted throughout the American Southwest.
The use of cultural control methods primarily refers the prevention of noxious weed infestation through the modification or elimination of land use practices by humans which may indirectly cause or aid in the spread of noxious weeds. There are generally five aspects to cultural control, which include: 1) prevention, 2) livestock manipulation, 3) wildlife manipulation, 4) soil disturbance activities and 5) public uses. To effectively control saltcedar, the use of some form of cultural control is often necessary.
The use of physical control is a control strategy commonly used on target species and often serves as the "foundation" of the integrated weed management effort. Physical control usually falls under three categories: 1) manual control, which can be as simple as hand pulling of the weed species (seedlings or mature herbaceous weeds generally) to eliminate individuals and reduce the seed source for usually very small infestations, to using hand tools like a hoe, loppers or a machete; 2) mechanical control, which involves the use of power tools (chainsaws/ clearing saws) and heavy equipment (tractors & bulldozers); 3) Control via fire, which is normally achieved through the use of prescribed burns. However, "let burn" designations for specific plant communities during wildfire situations can be an opportunity to explore when controlling target species. Often, prescribed fire is necessary when faced with mature stands of saltcedar. Resulting burns will usually achieve some level of mortality of the target species though very rarely eliminates the entire problem, but allows for access in to the vegetative stand for secondary treatment with mechanical and chemical control methods.
For the majority of weed infestations, the selective use of herbicides is necessary to accomplish the objectives of the control effort. The use of herbicides, in conjunction with cultural and mechanical control methods, usually result in the most effective levels of control on saltcedar (Egan et al 1993). The decision to selectively use herbicides requires a comprehensive planning effort and is site, as well as species specific. There are five important questions that must be answered when considering the use of herbicides as an element to an integrated control approach: 1) what herbicides are effective in producing a high level of mortality with a minimal need for re-treatment; 2) what are the effects of the herbicide on nontarget species, including residual effects of the herbicide to the soil; 3) what is the most effective and cost-efficient mode of application; 4) are properly trained personnel available to apply the herbicide; and 5) are there local, state or federal restrictions for the use of a particular herbicide.
The concept of IWM, as discussed above, refers to the "classic" understanding of IWM: the integrated use of cultural, physical, biological and chemical control strategies to contain or eradicate a population of noxious weeds. There are "other" aspects of IWM which may have been overlooked in the previous discussion, especially those related to weed infestation on open rangelands. Integrated weed management on rangelands involves the use of several control techniques in a well-planned, coordinated, and organized program (Sheley 1995). In Sheley's article, he discusses the need for inventory as the first phase of IWM. The goal is to determine and record the weed species present, the size of the area infested, the density of the infestation, whether other rangelands are under threat of invasion, soil and range types affected and other site factors pertinent to successfully managing weed-infested rangelands.
Planning and implementation is the second phase of IWM (Sheley 1995). Planning is the process by which problems and solutions are identified and prioritized, and an economic plan of action is developed to provide direction for implementing the control program. Implementing an IWM plan includes: 1) preventing weed encroachment into uninfested rangeland; 2) detecting and eradicating new weed introduction; 3) containing large-scale weed infestations; 4) controlling large-scale infestations using an integrated approach; 5) revegetation of control sites when and where appropriate; 6) Adoption of the proper range management practices (cultural control) in conjunction with the development of a weed management program; and 7) Monitoring and evaluation of the IWM plan itself. Monitoring and evaluation are the keys to determining if weed and/or grazing management plans are meeting plan objectives and are the prime determining factors used in altering IWM plans.
Now I want to discuss the practice of IWM on the saltcedar infestation specific to Afton Canyon, located along the Mojave River. The Afton Canyon area was designated an Area of Critical Concern (ACEC) in 1989 (Egan et all 1993). One of the objectives in the management plan for Afton Canyon is to improve riparian habitat and increase surface flow through the removal of saltcedar. In 1992, the Barstow Resource Area decided to tackle the large-scale saltcedar infestation (500 acres+) occurring in Afton Canyon. A decision was made to form an interdisciplinary team which would formulate an integrated strategy to contain and control this large-scale infestation. An inventory was conducted using existing data, recent infrared aerial photography and associated groundtruthing. With the inventory information available, the BLM proceeded into the planning phase to identify and prioritize areas within the canyon were identified and prioritized in relation to appropriate strategies to contain this infestation. We selected that portion of the canyon which we felt had the highest site potential for control and that would assist in control efforts downstream. The selected control area supported large mature stands of saltcedar, surface water flow and a small relict population of native trees. This portion of the canyon was both historically and currently grazed by cattle and was subject to periodically high levels of off-highway vehicle (OHV) use. During the planning phase, the BLM established monitoring plots to document the existing situation and characterize the vegetative components of the canyon. Monitoring plots identified existing ground and canopy cover and were numerically, as well as photographically, analyzed throughout the subsequent control effort. In addition, cross-channel vegetative trend transects were established to quantify ground cover and existing plant species frequency. It was found to be extremely important to fully document how the area selected for control appeared prior to treatment. This information always proves extremely valuable in the monitoring and evaluation phase of IWM. For similar control efforts, extensive photography is highly recommended.
In July, 1992, we ignited a prescribed fire in the canyon with the hope of maximizing saltcedar mortality and to open up the largest stands of mature saltcedar for secondary physical control. The fire resulted in an approximate 50 acre burn, which did result in a high initial mortality and was successful in opening up these area for secondary treatment. Since 1992, an aggressive control and site restoration effort has dramatically reduced the saltcedar population on public lands in Afton Canyon. The primary control strategy selected was the combined use of hand tools, chainsaws and clearing saws (e.g. physical controls) with concurrent herbicide use (e.g. chemical control) following a fire prescription.
This strategy is commonly referred to as the burn and cut method. It was found to be important to cut the trees s down to as close to ground level as possible and then, as shortly after cutting as possible, applying the herbicide directly with a compression sprayer onto the interior of the exposed stumps or stems. This method most effectively allows the herbicide to translocate directly to the root system and effectively kills the plant. Although this method can be very labor intensive, it does result in a high initial mortality rate, reducing the need for retreatments and allows for the removal of saltcedar from the site, which in turn allows for more rapid natural revegetation.
There has been a low to moderate level of re-sprouting, particularly in burn areas, which require a foliar herbicide application directly onto the re-sprout. There is a much lower level of re-sprouting and thus re-treatment with the cut stump method, but keep in mind there is going to be some level of retreatment necessary. There are four herbicide trade names that have been identified as effective in the control of saltcedar: Garlon 4, Pathfinder II, Rodeo and Arsenal (though the latter is not approved for use in Calif.).
The need for periodic monitoring and evaluation is key to a successful IWM strategy. The planning process needs to be dynamic, rather than static. Our initial planning efforts identified the need to revegetate the treated area with native trees and native riparian vegetation, which will ultimately provide much higher value wildlife habitat than the removed saltcedar. Initially, the need to modify or eliminate on-going land use practices was discussed, however this became even more evident as the BLM spent more time in the canyon. Portions of the Nojave Road were re-routed to reduce OHV use in the treatment area and in 1994, a three mile length riparian management fence was constructed both to exclude cattle and OHV from our treatment area, in order to provide the maximum protection for both natural and planted revegetation efforts (e.g. cultural control). As the Mojave River is an "open" system, with upstream lands primarily under private management, there will be an abundant seed source for possible re-infestation from upstream for some time to come.
However, we hope through education that those private land owners will become aware of the need to control saltcedar, for everyones benefit. The long term outlook on containing this particular large-scale infestation is limited to that which can be accomplished on a small downstream area of federally managed lands and any upstream assistance the BLM can receive from private land owners. This is likely to be the case for the majority of lands currently infested with saltcedar (Lovich et al. 1994).
Egan, T.B., R.A. Chavez and B.R. West. 1993. Afton Canyon saltcedar removal first year status report. In, L. Smith and J. Stephenson (tech. coords.), Proceedings of the Symposium on Vegetation Management of Hot Desert Rangeland Ecosystems. Phoenix, AZ.
Lovich, J.E., T.B. Egan and R.C. De Gouvenain. 1994. Tamarisk control on public lands in the desert of Southern California: two case studies. Proceedings of the 46th Annual California Weed Conference, California Weed Science Society. San Jose, Calif.
National Park Service 1990. Guidelines for Coordinated Management of Noxious Weeds in the Greater Yellowstone Area.
Oregon State Univ., Coop. Extension 1993. Oregon Pesticide Applicator Manual. A Guide to the Safe Use and Handling of Pesticide.
Sheley, R.L. 1995. Integrated Rangeland Weed Management. Rangelands 17(6):222-223 December, 1995.
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