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Assessing Biological Control Agents for Area-Wide
Integrated Pest Management (IPM) of Leafy Spurge
    with foci in Montana and South Dakota

Jack Butler

Question 1: What major problem or issue is being resolved and how are you resolving it?

Leafy spurge (Euphorbia esula L.) is an exotic plant species accidentally introduced into North America in the late 1800's. Much of the current research emphasizes conventional and integrated control programs utilizing herbicides, biological insect control (Gagne, 1990, Gassman and Shorthouse, 1990, Pecora et al., 1989), and behaviorally encouraging lambs and goats to preferentially graze on leafy spurge (Walker et al., 1992).

The success of this exotic species is due in part to its ability of tolerate and exploit a variety of habitats and environmental conditions (Morrow, 1979). The objective of this study is to document the micro-scale distribution, density, dynamics and trends of leafy spurge populations in response to flea beetle control within Montana and South Dakota study areas. Sites specifically selected for detailed study represent the wide range of topographic, soil, vegetation, and landform situations typical of the regions.

1. Document leafy spurge population dynamics in response to control by two species of flea beetles (Aphthona nigriscutis and A. lacertosa).

2.Determine the role of selected site characteristics (slope, aspect, soil texture, soil moisture regime, topographic position) on establishment and persistence of two species of flea beetles.

3.Evaluate the response of native plant species to control of leafy spurge by two species of flea beetles.

4.Evaluate the long-term effect of biological control by the two species of flea beetles on the soil seed bank of leafy spurge and native plant species.

During the 1998 field season, 52 and 41 permanently located sample sites were established within the Mill Iron (Montana) and South Fork of the Moreau River (South Dakota) Leafy Spurge Study Areas, respectfully. The original goal was to select a minimum of 150 sample sites within the two Study Areas. However, the number of suitable sample sites was limited, especially in South Dakota. The 93 selected sites represent the wide range of topographic, soil, vegetation, and landform situations typical of the Study Areas. The GPS location for each site (latitude/longitude) was regarded as the center of the sample site, which was marked with a fiberglass post (primary marker), and PVC pipe (secondary marker). Each primary and secondary marker contains a unique identification label.

A base-line transect was established perpendicular to the slope at each sample site with the survey marker serving as the center. Ten transects (5 upslope and 5 downslope) were placed at 30 degree intervals from the survey marker. A 5 X 4 m plot, with the primary survey marker in the center, and six randomly located transects (3 upslope and 3 downslope) were used for sampling flea beetle populations. Sample sites located near previous flea beetle release sites were swept to determine presence of established flea beetle populations.
The COAST digital imaging system was used to acquire an image in the center of each sample site. The base of the camera rod was placed in such a fashion as to minimize shadows in the image. Images were also collected from 4 randomly selected points (2 upslope and 2 downslope) 2.5 m from the center of the sample site for a total of 5 images per sample site. A 20 X 50 cm Daubenmire quadrat was placed within each of the 11 image plots. Density of leafy spurge and foliar cover of all plant species occurring in the quadrat were estimated. Cover estimates were recorded using the Daubenmire cover class system (1=0-5%, 2=6-25%, 3=26-50%, 4=61-75%, 5=76-95%, and 6=95-100%). The mid-point of each cover class will be used to calculate average cover values for each species. A physical inventory of each sample site was made that included aspect, slope, topoposition (convex/concave position) soils series/type, range site, and other notable features using the TEAM Leafy Spurge Site Information Form.

Soil Samples were collected from 20 study sites (10 release sites and 10 control sites) in each of the two Study Areas (Montana and South Dakota). Ten soil samples (5 upslope and 5 downslope) were randomly collected within 3 m of the center of each permanently located sample site. Each soil sample consisted of a 5 cm soil core taken to a depth of 3 cm. The five samples collected from each upslope position within each site were placed in a common container and thoroughly mixed. Five equal-size samples were then collected from the container and used in emergence trials conducted at Central Missouri State University. Each sample was uniformly spread on top of a 2 cm thick sterile vermiculite-peat moss mixture in a standard seeding flat. The same procedure was used on the downslope samples. Flats were randomized in a walk-in environmental chamber and given a weak nitrogen-phosphorous-potassium (N-P-K) solution once a week and watered as needed. Flats were exposed to a 12-hour photoperiod while the temperature alternated as described by Bowes and Thomas (1978). Each set of samples was monitored for a period of eight weeks. Emerging seedlings were recorded weekly and removed. After eight weeks, the surfaces of the samples were scratched and seedling emergence monitored for an additional four weeks. Mean seed densities were calculated and will be used to evaluate the long-term effect of biological control on the soil seed bank of leafy spurge and native species. Composition of the soil seed bank will be compared to extant vegetation in both infested and noninfested sites.

Species composition of each sample site and average cover values for the native species and leafy spurge were calculated from information collected using the Daubenmire cover class system. Foliar cover of leafy spurge was determined using the COAST system and compared to values recorded using the Daubenmire Cover Class System. Average cover values of the native species will be used to calculate Shannon Diversity Indices for each sample site. The potential relationships between foliar cover of leafy spurge (using both the COAST system and the Daubenmire Cover Class system) and density of leafy spurge, cover of native species, and native species diversity will be evaluated using standard regression techniques. Information on flea beetle composition and abundance collected during the 1999 field season will be added. These data will be used as a baseline in evaluating the micro-scale effects of control on plant species composition over the duration of the TEAM Leafy Spurge project.

Question 2: How serious is the problem? Why does it matter?

Leafy spurge is now well established throughout much of the Northern Great Plains. Heavy infestations of leafy spurge dominate and displace many native plant species. Lym and Messersmith (1987) reported that leafy spurge infestations can reduced carrying capacity for livestock by 50-75%, with much of this loss attributed to decreased forage production and avoidance of infested sites (Lym and Kirby 1987, Hein and Miller 1992). Similar reductions in habitat use by native ungulates on leafy spurge infested sites were reported by Trammell and Butler (1995) for Theodore Roosevelt National Park, North Dakota.

Question 3: How does it relate to the National Program(s) and National Program Component(s) to which it has been assigned?

The TEAM Leafy Spurge project is a part of the USDA/ARS Area-Wide Management Program. It is a component of Crop and Commodity Pest Biology, Control and Quarantine (304). TEAM Leafy Spurge complements efforts to develop new and improved pest control technologies and assess component technologies for integrated pest management (IPM) systems.

Question 4: What were the most significant accomplishments this past year?

Plant species composition and cover, and flea beetle abundance were evaluated during the 1999 field season for all selected sample sites in Montana and South Dakota using procedures described above. In addition, vegetation composition data collected during the 1998 and 1999 field seasons have been summarized and incorporated into a Geographic Information System (PC ArcView).

Question 5: Describe the major accomplishments over the life of the project, including their predicted or actual impact.

At total of 93 permanent sample sites (60 flea beetle release sites and 33 control sites) were established within the Montana and South Dakota portions of the TEAM Leafy Spurge project area. Approximately 6,000 beetles (3,000 Apthona lacertosa and A. nigriscutis) were released in June 1998 at each of the 60 release sites. Abundance and composition of flea beetles were evaluated during the 1999 field season. Plant species composition and density and cover of leafy spurge in relation to biological control by flea beetles were evaluated on all sample sites.

Question 6: What do you expect to accomplish, year by year, over the next 3 years?

We expect to continue monitoring the establishment and persistence of flea beetles on both release and control sites during each year of the next three years. The recovery of native and forage vegetation following control of leafy spurge will be carefully monitored and evaluated every year for the next three years. In addition, soil seed bank analysis will be conducted using the described protocol in October 2001 and compared to the initial 1998 data. Range site descriptions will be prepared in 2000 and 2001 and used to determine potential plant communities for the Montana and South Dakota Study Areas. Existing plant communities will be evaluated from a series of randomly selected points within each range site. The goal is not to evaluate range condition of non-infested sites, but rather to compare species composition between infested and non-infested areas within each range site. A major goal for the 2000-2002 portion of this project is to compile all of the physical and biological information collected over the four year study period into a geographic information system (PC ArcView).

Question 7: What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end user (industry, farmer, other scientists)?
What are the constraints, if known, to the adoption and durability of the technology products?

My research crew and I participated in demonstration trials for area land managers (private and public) at our study sites in Montana and South Dakota. I also attended a demonstration trial at the Wyoming study site. Further, I actively participated in SPURGEFEST 99 and in the Annual Leafy Spurge Symposium. End users were able to directly experience the potential effects of biological control of leafy spurge.

The expected output of this project will include an analysis of the efficacy of flea beetle control under a wide variety of physical and biological conditions in western South Dakota and eastern Montana. This will include recommendations for the selection of release sites that have the greatest potential of effecting control of leafy spurge both in terms of the extant infestation and the soil seed bank. Detailed descriptions of specific sites that have the lowest potential of control, either because of reduced establishment of flea beetles and/or persistent seed bank, will also be included. These recommendations could possibly be presented in a simple dichotomous key that could be used by land managers/owners in selecting release sites. This document could easily be integrated with the results from the other Ecological Assessment teams in Wyoming and North Dakota producing an area-wide management plan. This information should be available to the end user at the conclusion of the ecological assessment portion of TEAM Leafy Spurge (May 2002). I do not anticipate any constraints at this time.

Question 8: List your most important publications in the popular press and presentations to non-scientific organizations and articles written about your work.

Impacts of leafy spurge on local and landscape patterns of plant species diversity in Theodore Roosevelt National Park. Dan R. Cogan and Jack L. Butler. Paper presented at the annual Leafy Spurge Symposium, June 26-27, 1999 Medora, North Dakota.

Question 9: Scientific Publications

Barkosky, Richard A., Jack L. Butler, and Frank A. Einhellig. 1999. Mechanisms of hydroquinone-induced growth reduction in leafy spurge. Journal of Chemical Ecology. 25:1611-1621.

This work was supported by the Cooperative State Research Service, U.S. Department of Agriculture under agreement NO. 94-38300-0282.11.

Trammell, Michael A. and Jack L. Butler 1995. Effects of exotic plants on native ungulate use of habitat. Journal of Wildlife Management. 59:808-816.
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