Area-wide Weed Management

The extension delivery and area-wide evaluation of new biologically-based technologies for control of three exotic invasive pest plants in several western ecosystems from Colorado to California and from Mexico north to Canada, with special emphasis on saltcedar.

Overview: The invasion of exotic saltcedar has been characterized as one of the worst ecological disasters to befall western riparian ecosystems. Due to the highly destructive nature and its invasive potential, saltcedar has caused extensive agricultural, economic and environmental losses (Lovich et al. 1994, Lovich and DeGouvenain 1998, Dudley et al. 2000, Zavaleta 2000). At the request of several public and private groups, USDA-ARS initiated foreign exploration and host-specificity testing for biological control agents nearly ten years ago. As currently documented, Tamarix biological control presents a minimal environmental hazard as no agricultural or North American native plants are known from the family Tamaricaceae. The Nature Conservancy has stated that: "Tamarisk is probably the most suitable of "ecological weeds" for investigation of biocontrol. It belongs to a family not native to North America and has only marginal economic use. Its costs, in terms of floodplain management and water consumption, are high, and as will be discussed below, biocontrol agents may be available. However, the U.S. Department of Agriculture must be lobbied to undertake the long and expensive task to developing a biocontrol strategy. Since tamarisk is not an agricultural pest, THE USDA must be specifically encouraged to commit resources" (The Nature Conservancy, Elements of Stewardship Abstract for Tamarixspp., http://tncweeds.ucdavis.edu/esadocs/documents/tamaram.htm).

Following years of research and testing the first tools for biological control of this exotic pest plant have now been made available and applications have been approved for agent introduction. Through an extensive 3 year review period, the USDA and the USDI have discussed the development and implementation of a biologically-based management program for saltcedar in the western US. Although most USDA and USDI Agencies believe that saltcedar control is not only desirable but essential for the survival of many threatened and endangered species, some have expressed concern. Concerned parties include the Endangered Species Division of the FWS who have worried that such action might jeopardize an endangered subspecies of the southwestern willow flycatcher and therefore have forestalled the release of saltcedar natural enemies. Others including many in the FWS feel that saltcedar is the primary reason that flycatcher populations are now in jeopardy and are actively pushing for biological control of this pest plant (see DeLoach et al. 2000, Dudley et al. 2000). Following several in-depth planning meetings with the FWS and Consortium members, a plan was devised and permits issued, for activities that would test the use of natural enemies to control saltcedar in 13 different release sites in six western states. Through cooperative action of the Consortium and other agencies; the sites are to be closely monitored for biological control effectiveness; natural enemy population growth and spread; the effects of the program on local vegetation (reduction in the target species and both positive and unsuspected negative effects on desired vegetation); and indirect foodweb and habitat alteration effects on associated wildlife species. Unfortunately, no specific resources have been made available to conduct these assessments in a holistic manner. Therefore the Consortium has developed a detailed action and monitoring plan (see Gould 2000) and is attempting to acquire resources from associated Agencies. This has been successful to some degree as all cooperating groups in the Consortium are providing in-kind services and some monetary support but the few funds are available to conduct the implementation project steps as needed to ensure success while documenting the safety of biological control. This is of paramount importance as saltcedar biological control is a critical test case. It is then imperative that this program be conducted in a comprehensive and open fashion.

The Consortium implementation program consists of three primary stages. 1) Field cage releases of selected natural enemies with initial data collection on agent establishment, developmental biology and impact assessment (to be conducted under minimal cage containment). 2) Open field release into the local environment, linked with detailed monitoring for assessment of insect population growth and spread in the local environment, agent impact on saltcedar growth and population control, and associated direct and indirect effects that it may have on other flora and fauna in the release areas. 3) Agent redistribution and release to other areas highly affected by invasive saltcedars. In conjunction with each stage of this program, the Consortium has designed detail implementation and monitoring plans that it hopes to conduct for comprehensive assessment of the program. The tests were begun in the late summer of 1999 with the field cage release of the Tamarix leafbeetle, Diorhabda elongata that originates from western China and Kazakhstan (see Gould for a 1999 project summary). The project is now ready to begin open field releases, however, without additional resources, the Consortium is concerned that these evaluations will take too long and not provide enough effective data to satisfy program skeptics. The Consortium thus requests resources to address the following objective.

Objective 3: Implementation of large-scale field tests for saltcedar biological control and the monitored effects of both saltcedar and its biologically-based management on associated plants, wildlife and other attributes of the local ecosystem.
Justification: Detailed monitoring plans for release of the leaf beetle, D. elongata have been prepared by the Consortium Monitoring Team and distributed to interested parties who reviewed and approved them. These plans cover 1) monitoring the control insect and its effect on saltcedar inside the release cages during year 1 before open field releases, 2) monitoring of the control insect biology, effect on saltcedar and dispersal after open release, 3) monitoring of vegetation before release and recovery after control, and 4) monitoring of wildlife before and after control. The full set of monitoring plans may be accessed on the Homepage of the UC Davis Weed Resource and Information Center (http://wric.usdavis.edu/exotic/exotic.htm).

The three subobjectives and the associated methods for monitoring are as follows.

Subobjective 3a: Monitoring of biological control insects and their rate of dispersal, assessments of their impact on saltcedar, and possible detection of feeding on non-target plants. A comprehensive set of release protocols and monitoring plan details have been developed that cover the following subobjectives:
1) Determine establishment of self-sustaining, year round populations of control insects
growing on saltcedar plants in nature.
2) Quantify reproduction, development, mortality (parasitism, predation, disease), and population increase of the control insects in nature.
3) Describe behavior, mating, oviposition, feeding by immatures and adults, and part of plant utilized for feeding and development of immatures and adults.
4) Determine the seasonal cycle, number of generations, and overwintering success.
5) Quantify distance of dispersal of the control agents over time.
6) Quantify the amount of damage caused and the degree of control of saltcedar.
7) Quantify any feeding or reproduction on any non-target plant species.

Methods: The monitoring methods include a combination of counts taken from random branch samples within differing strata of the release plot moving from the center of release out in concentric circles; transect counts assessing defoliation and insect numbers at key times within the season; and phenology assessments made on sleeve caged sentinel representatives held on selected plants in the field. Cohorts of eggs will also be placed and monitored on specific test plants to establish generational survival and defoliation rates at specific sites. For open field population assessment, eggs will be used as a stage-specific indicator as they are immobile, easy to see and they persist for the longest period of any non-flying life-stage. To estimate population numbers, scouts will count the number of eggs that are laid on 100 sentinel branches that are sampled repeatedly. Samples will be timed to occur just following peak oviposition for each generation. Sentinel branches and the associated plants (25/ plot) will be randomly selected in advance from aerial photographs and used in spatial analysis to map population densities in the release areas. In addition to egg counts, plant characteristics such as size, percent defoliation, abundance of other damaging insects will be assessed. To characterize dispersal, both short and long-range sampling protocols have been developed that use visual detection of insect life-stages and plant damage. Since D. elongata is the only defoliating insect affecting saltcedar, these signs are good indicators of the target insect. Delineation sampling will be conducted using GPS units to circumscribe the obvious infested areas. For longer scale dispersal, permanent monitoring points will be set up at 1km distances along four 8 km transects that radiate from the original release site. All life stages will be assessed in the sampling, along with estimated defoliation levels. Long range dispersal will only be assessed once each season at 13 extensive release sites but will be evaluated in more detail and at a higher rate of frequency at the three Task 2 sites. Monitoring of development and reproduction will be performed twice weekly at Task 2 sites. Monitoring at the other sites will be at 2 to 4-week intervals throughout the growing season. Monitoring of population increase and damage to saltcedar and non-target plants, and of dispersal of the control agents will be done at the peak adult population of each generation, or 2 to 3 times during the growing season.

Subobjective 3b: Conduct vegetation monitoring pre and post release of the biological control insects, to assess the quantity and impact of defoliation on saltcedar; to correlate defoliation with individual plant damage and population suppression and to characterize shifts in woody plant diversity and density and that of understory vegetation if saltcedar declines.

Methods: Detailed baseline data on vegetation species composition and structure will be taken at each site prior to release of control insects and annually thereafter for 4 years. Measurements will be made of the following characteristics: Plant volume, plant morphology and condition - canopy density, photo flux, leaf area, foliage color, and reproductive status. Vegetation assessments will be conducted using a three component sampling scheme, 1) regular assessment of caged plants exposed to differing levels of beetles, 2) periodic monitoring of 100 randomly selected and premarked plants/ 10 hectare plot, and 3) coarse resolution vegetation characterization of habitats using aerial photography (see figure 5). Herbivory will be assessed within and outside of cages by measuring branch length, damaged tissue, number of secondary branches and inflorescences affected, and regrowth of damage tissues. Associate woody vegetation (saltcedar, beneficial species, and others) will be assessed using nearest three neighbor methods and understory vegetation will be characterized using 1 m. sq. quadrates at a distance of 0.5 meters from selected Tamarix plants. In all cases, associated soil characteristics will be assessed, including salinity levels.

Subobjective 3c: Wildlife monitoring will be conducted to determine the effect of the biological control agents on wildlife populations (especially species of concern), through altered densities of saltcedar, and through the anticipated recovery (or lack of recovery) of native plant communities. This will be done to quantify abundance and species diversity of indicator species, reproductive success, and changes in mortality factors of bird species and aquatic indicator species following biological control release.

Methods: The basic assumption of the FWS required wildlife monitoring plan is that saltcedar has some habitat value but that dense infestations reduce species and structural diversity of plants, reduced resources required by animals, reduce species and numbers of riparian birds, and reduce reproduction success compared with native vegetation. These factors may also adversely effect mammals, reptiles and fish. The study areas will be designed to contain a 10 to 20 km transect paralleling the watercourse. They will run from the release site upstream with plots (totaling 10 ha) centered on the release site in saltcedar habitat. Additional reference plots (totaling 10 ha) 8 to 20 km upstream will be sampled both in saltcedar and in desired cottonwood/willow habitat. Sampling methods include avian point counts along the transect, searches within the 10 ha plots, nest monitoring; catch and release of small mammals; catch and release traps with drift fences for reptiles and amphibians; surveys of indicator insect species; and transects across the stream to measure water and channel parameters. Baseline data will be taken before release of the insects or after release but before significant changes to vegetation occur Follow-up comparison surveys will be made during the 4th year of the grant. However, our wildlife biologists and the FWS suggest that additional wildlife surveys need to continue for at least 10 years after release of the biological control insects. These follow-up surveys will be conducted by Consortium affiliates (BLM, BR, BRD and others) following the end of this grant.