Progress 01/15/05 to 01/14/08
Outputs
OUTPUTS: The work conducted under this project was shared in a number of ways to influence both the science of developing herbicide management strategies, policy associated with genetically modified crops and to farmers to encourage preventive measures to avoid increased abundance of glyphosate resistant weeds. The quality and novelty of the work has been recognized through no fewer than 12 invited presentations at regional and national symposia addressing the subject of herbicide resistance management. In addition, members of the research team actively participated in several workshops hosted by the Northeast Weed Science Society in debating the content of, then writing the Glyphosate Stewardship plan authored by the Northeast Weed Science Society. In addition, members of the research team presented talks to farmers that reached audiences of some 3,400 farmers and input providers. Our published papers have appeared in such journals as Weed Science but also in the Journal of Applied
Ecology. One such paper was recognized as the Outstanding Paper appearing in Weed Science during 2006. This paper, selected from some 140 published during 2006, details controlled environment wind-tunnel studies with Conyza canadensis conducted here at Penn State. Another paper on a related subject was published in the Journal of Applied Ecology quantifies the long-distance dispersal of Conyza canadensis in the field and discusses the implications for glyphosate resistance management in the field. The subject of spread of glyphosate resistant weeds is incredibly important given 85% of the soybean planted in the state and region are glyphosate tolerant lines. Glyphosate resistant weeds threaten reduced tillage practices in soybean and corn in this region and cotton to our south.
PARTICIPANTS: Five faculty from four Land-Grant Universities were actively involved in this project. In addition, a doctoral student, Dr. Joseph Dauer successfully completed doctoral degree in the Ecology Inter College Graduate Degree Program at The Pennsylvania State University. Dr. David Mortensen and Dr. William Curran are both Professors in the Department of Crop and Soil Sciences Department at Penn State. Mortensen provided expertise in overall project guidance and coordination as well as in designing and analizing the field studies. Dr. Curran has a joint research and extension appointment and provided invaluable input on the design of the field survey program and helped line up farmer collaborators associated with the survey work. Dr. Elson Shields is a Professor in the Department of Entomology at Cornell University. His contribution included guiding the design and data collection of the remotely piloted aircraft experiment in which seed in the atmospheric boundary layer were
sampled. Dr. Mark VanGessel also holds a research and extension appointment at the University of Delaware. Dr. VanGessel was instrumental in guiding many of the field studies, particularly the remotely piloted aircraft study and the seedbank studies. Finally, Dr. Ed Luschei is a quantitative Ecologist in the Department of Agronomy at the University of Wisconsin. Dr. Luschei guided the development of the spatially explicit weed spread model. Dr. Joseph Dauer's doctoral degree was supported by funds from this grant. Dr. Dauer is the lead author on two papers associated with this work with another four either submitted or in preparation. While he continues to work diligently on publishing the papers, Dr. Dauer has moved on to accept a post-doctoral appointment at Oregon State University where he is conducting spatially explicit studies of weed biocontrol agents.
TARGET AUDIENCES: This research was presented at many regional, national and one international conferences by Mortensen, Dauer and by Curran. The results of this work were presented in invited symposia at the Northeast Weed Science Society; the Southern Weed Science Society; the Weed Science Society of America; the International Congress on Invasive Plants; the International Aerobiology Congress; and will be presented at the Ecology Society of America meetings in the summer of 2008. In addition to the invited papers, numerous volunteered papers have also been presented at the same meetings. Therefore, both agricultural, aerobiological and ecological scientists were exposed to this work. In addition, our work was incorporated into the Pennsylvania Lime and Fertilizer conference, and numerous extension and outreach meetings held in Pennsylvania, Delaware and Maryland. The audience attending those meetings would include farmers, input providers and outreach educators.
Impacts
The proposal addressed the problem of the evolution and spread of glyphosate resistant weeds in landscapes where glyphosate tolerant soybean is widely planted. Specifically, glyphosate-resistant C. canadensis populations were first documented several years prior to the initiation of this study. At that time, those populations were limited to the coastal region of Delaware and Maryland. They now infest greater than 44,000 hectares of arable land in the eastern United States, only five years after the first resistant population was reported. Clearly, seed dispersal, the expansive use of glyphosate and the lack of tillage are all factors contributing to this high invasion speed. Our study set out to document the pattern of dispersal of this troublesome weed. We focused on this species because it was the first species of agronomic importance to evolve resistance and because resistance in a winter annual threatens conservation tillage practices widely in use in this crop.
From nearly five years of work we've documented that horseweed disperses far greater distances than previously reported for any wind-dispersed plant species. Reviewers of our papers have commented that the basic understanding of seed dispersal has been expanded significantly with "the most extensive dispersal kernel data set in existence". We actually measured seed movement to 1000 m from source plants but more importantly when we employed remotely piloted aircraft we documented that weed seed routinely move into the boundary layer (where we trapped them with remote controlled planes) and estimate once in the atmospheric boundary layer, the seed move 10's of kilometers a day. The practical significance of these findings are that management in individual fields is highly interconnected. We conclude that the only reasonable way to manage this problem is to invoke area-wide management of this important pest problem. We explored several scenarios of area-wide management using a spatially
explicit model that couples our empirical results with a landscape-scale plant population dynamics model. There we concluded that developing buffers of some 5 km in width and or reducing the proportion of acres planted to glyphosate tolerant soybean would be the most effective methods of containment and management.
Publications
- Dauer, J., D.A. Mortensen, and M. VanGessel. 2007. Spatial and temporal dynamics governing long distance dispersal of Conyza canadensis. Journal of Applied Ecology 44:105-114.
- Isard, S. A., D. A. Mortensen, S. J. Fleischer and E. D. De Wolf. 2007. Application of Aerobiology to IPM. In Integrated Pest Management Systems. CRC Press. (In Press)
- Dauer, J., E. Luschei, and D. A. Mortensen. 2007. Effects of Glyphosate-Resistant Crop Adoption on the Connectivity of a Landscape: An Herbicide-Resistant Weed Perspective. Journal of Applied Ecology. (Pending)
- Dauer, J., D. A. Mortensen, M. VanGessel, and E. Shields. January, 2008. Movement of Conyza seed in the planetary and atmospheric boundary layer. Journal of Forest and Agricultural Meteorology. (Pending)
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Progress 01/15/06 to 01/15/07
Outputs
The dispersal of herbicide resistance genes via pollen or seed has the potential to connect farmsteads once thought to be independent. The implications of such interconnections have taken on new importance as the appearance of herbicide resistant biotypes increases and reliance on herbicide use in genetically modified crops increases. The adoption curve for genetically modified glyphosate-resistant soybeans, cotton, and corn is unprecedented. Glyphosate is a non-selective herbicide now applied to more than 25 million hectares, approximately 85% of total soybean. While its use has reduced overall weed abundance, glyphosate represents a strong selection pressure for glyphosate resistant survivors. Through this research we have demonstrated that glyphosate-resistant horseweed (C. canadensis) populations now infest greater than 44,000 hectares of arable land in the eastern United States, only five years after the first resistant population was reported. Clearly, seed
dispersal, the expansive use of glyphosate and the lack of tillage are all factors contributing to this high invasion speed. Seed collected from deliberately established horseweed source populations were found at the outmost seed traps in our empirical studies. These results indicate seed regularly disperse at least 500 m from source populations. While a relatively small number of seed move great distances, 99% of the seed were found within 100 m of the source. An empirical and a mechanistic model were fitted to the data to predict the dispersal in the prevailing wind direction. Both models underestimated seed deposition beyond 200 m but the mechanistic model provided a better fit to the data (lower AIC). A two-dimensional analysis examined the correlation between angular directions of wind and seed movement. All trials were anisotropic, but only the cumulative wind and seed direction were significantly correlated (p<0.05). The empirical model was used to explore the effect of
increasing source strength which might be expected as an infestation of glyphosate-resistant C. canadensis expands on a producer's farmstead. At infestation levels consistent with a heavy infestation in a 5 ha field, seed may disperse nearly 3 km, easily affecting tens to hundreds of surrounding farmsteads.
Impacts
Movement of horseweed seed from one farmstead to adjacent farmsteads within a 5-10 km radius commonly occurs in the farming region studied. As the seed move, farmers incur an increase of 5-12 dollar per acre cost in weed control. These results demonstrate that herbicide management plans must take an area-wide approach to management.
Publications
- Dauer, J., Mortensen, D.A., and Humston, R. 2006. Controlled experiments to predict horseweed (Conyza canadensis) dispersal distances. Weed Science 54:484489.
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Progress 01/15/05 to 01/14/06
Outputs
Weed invasions follow a general pattern; seeds sample heterogeneous environments, successfully establish and adapt to local conditions, then continue to spread to new uncolonized sites. Ours is an invasion problem that in some ways fits this description and in other ways not. Our proposal seeks to quantify the dispersal and establishment potential of invasive weed biotypes, with an emphasis on herbicide resistant biotypes. The study system deviates from the Sakai model in one important way, seed sources can arise from short- or long-distance emigration and through the development of locally resistant populations that become seed sources for the next dispersal event. The study system involves a very important problem weed, horseweed, Conyza canadensis, common to reduced and no-tillage crop fields, roadsides and abandoned fields. Development and spread of glyphosate resistant populations threaten the long-term sustainability of no-tillage cropping practices and promises
to significantly increase cost of weed management in such systems. In this research, we take a spatially explicit approach to determine the bottlenecks to successfully containing the spread of a weed that could significantly alter the way weed management is performed in reduced tillage farming systems. We then assess the value of particular farming practices in minimizing the spread of glyphosate resistant horseweed. We conduct these analyses in a spatially explicit context, meaning we look at the influence of such practices in the context of a population of fields in a landscape mosaic with fields being interconnected by dispersal of horseweed. The value of a spatially explicit approach, underscored in the recently published Ecological Effects of Pest Resistance Genes in Managed Ecosystems, is that it enables us to address a pest management problem and solution at the relevant spatial and temporal scale. Our project sets out to define the potential rate of spread of this weed through
the combination of life history and seed dispersal studies. During the 2004 and 2005 field season, we determined that horseweed seed are moving considerably greater distances than originally realized. In a two-dimensional field based seed trapping experiment, horseweed seed were found at distances of 500 meters from source plants. In preliminary experiments with remote controlled airplanes we found seed up to 100 meters above the ground surface. Preliminary simulations indicate that seed at that altitude with an exceedingly low settlement velocity could easily move 10-40 km in a day. Thus far, the findings of this research underscore the reality that agricultural fields are highly interconnected. That management in one field impacts the management of weed pests in another other fields in a local area, an area considerably larger than previously thought.
Impacts
Conyza canadensis, horseweed, an important weed in soybean, corn and cotton production across the U.S., has evolved resistance to glyphosate herbicide. Members of the Pennsylvania Soybean Board recently stated that this was the greatest threat to soybean production in the region (the Board's statement at their recent annual meeting, February 2002). Resistant populations limited to 26 fields in Maryland, Delaware and southern New Jersey in 2001 grew to 300 fields in the 2002 field season. It now also occurs in 10 eastern states in soybean and cotton fields covering greater than 44,000 hectares. The spread of glyphosate resistant horseweed has increased the cost of weed control by requiring additional herbicides and tillage. Because horseweed is a winter annual, it is particularly troublesome where farmers have adopted conservation tillage practices. Development and spread of glyphosate resistant populations threaten the long-term sustainability of no-tillage cropping
practices and promises to significantly increase cost of weed management in such systems. Our project sets out to define the potential rate of spread of horseweed through the combination of life history and novel landscape scale dispersal studies. Finally, a spatially explicit landscape population dynamics model will be used to assess the influence of a range of management strategies on the degree of horseweed containment.
Publications
- Hilgenfeld, K.L., Martin, A. R., Mortensen, D. A. and Mason, S. C. 2004. Weed management in a glyphosate resistant soybean system: weed species shifts (Glycine max) . Weed Technology. 18:284-291.
- Hilgenfeld, K.L., Martin, A. R., Mortensen, D. A. and Mason, S. C. 2004.Weed management in glyphosate resistant soybean: weed emergence patterns in relation to glyphosate treatment timing. Weed Technology. 18:277-283.
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