David Mortensen, Ph.D.

David Mortensen, Ph.D.

  • Professor of Weed and Applied Plant Ecology
422 Agricultural Sciences and Industries Building
University Park, PA 16802


  • Ph.D., Crop Science, North Carolina State University, 1987
  • M.S., Botany, Duke University, 1983
  • Undergrad. Degree, Botany, Drew University, 1978

Responsibilities and Interests

Broadly, I apply my background in applied plant ecology and ecologically-based pest management to improve the sustainability of land resource management. My work explores the interplay between the ecology of agricultural fields, field edges and forest fragments. My work takes a landscape approach to assessing this interplay. An example of such work assesses approaches to integrating weed management with the goal of reducing reliance on herbicide use. A summary of this work was recently published in an important paper that appeared in the journal BioScience (see below).  I have a long-standing interest in making weedy plant management more sustainable through understanding how management tactics interact. Finally, I work on methods of enhancing weedy plant invasion resistance in northeastern forests. I balance my research interests with teaching such courses as: Principles of Weed Management, Flora of the Central Appalachian Region, and Ecology of Agricultural Systems. Finally, my interest in local food systems drew me to our University Community Garden where I am a gardener and faculty advisor. 


  • 70% Research
  • 30% Teaching


Selected Recent Publications

  • Mortensen, DA, JF Egan, BD Maxwell, MR Ryan, and RG Smith. 2012. Navigating a Critical Juncture for Sustainable Weed Management. BioScience, 62: 75-84.
  • Egan, JF and DA Mortensen. 2012. A comparison of land sharing and land sparing strategies for conserving plant species richness in agricultural landscapes. Ecological Applications, 22: 459-471.
  • Egan, JF and DA Mortensen. 2012. Quantifying vapor drift of dicamba herbicides applied to soybean. Environmental Toxicology and Chemistry, 31: 1023-1031.
  • Egan, JF, BD Maxwell, DA Mortensen, MR Ryan, and RG Smith. 2011. Stewardship for herbicide-resistance crop technology. PNAS, 108(11) E38.
  • Smith, R.G., A.G. Hulting, M.E. Barbercheck, and D.A. Mortensen. 2011. Yield and net returns during the transition to organic feed grain production. Agronomy Journal, 103:51-59.
  • Ward, MJ, MR Ryan, WS Curran, DA Mortensen, and ME Barbercheck. 2011. Cover crops and disturbance influence activity-density of Amara aenea and Harpalus pensylvanicus (Coleopetera: Carabidae). Weed Science 59:76-81.
  • Mirsky, SB, WS Curran, DM Mortensen, DL Shumway, and MR Ryan. 2011. Timing of cover crop management on weed suppression in reduced-till soybean. Weed Science. 59: 380-389.
  • Nord, EA, WS Curran, DA Mortensen, SB Mirsky, and BP Jones. 2011. Integrating multiple tactics for managing weeds in high residue no-till soybean. Agronomy Journal, 103: 1542-1551.
  • Smith, RG, ME Barbercheck, DA Mortensen, J Hyde, and AG Hulting. 2011. Yield and net returns during the transitioin to organic feed grain production. Agronomy Journal, 103: 51-59.
  • Smith, RG, T Gareau, DA Mortensen, W Curran, M Barbercheck. 2011. Assessing and Visualizing Agricultural Management Practices: A Multivariable Hands-On Approach for Education and Extension. Weed Technology, 25: 680-687.
  • Ryan, MR, SB Mirsky, DA Mortensen, and WS Curran. 2011. Potential synergistic effects of cereal rye biomass and soybean planting density on weed suppression. Weed Science, 59:238-246.
  • Ryan, MR, WS Curran, AM Grantham, LK Hunsberger, SB Mirsky, DA Mortensen, EA Nord, and DO Wilson. 2011. Effects of seeding rate and poultry litter on weed suppression from a rolled cereal rye cover crop. Weed Science, 59: 438-444.
  • Rauschert, E.S.J., D. A. Mortensen, O.N. Bjornstad, A. Nord and N. Peskin. 2010. Slow spread of the aggressive invader, Microstegium vimineum (Japanese stiltgrass). Biological Invasions. 12:563-579.
  • Ryan, M.R., D.A. Mortensen, L. Bastiaans, J.R. Teasdale, S.B. Mirsky, W.S. Curran, R. Seidel, D.O. Wilson, and P.R. Hepperly. 2010. Elucidating the apparent maize tolerance to weed competition in long-term organically managed systems. Weed Research 50:25-36.
  • Smith, R.G., D.A. Mortensen, and M.R. Ryan. 2010. A new hypothesis for the functional role of diversity in mediating resource pools and weed-crop competition in agroecosystems. Weed Research 50:37-48.
  • Nord, A.N., D.A. Mortensen, and E.S.J. Rauschert. 2010. Environmental factors influence early population growth of Japanese stiltgrass (Microstegium vimineum). Invasive Plant Science and Management, 3:17-25.
  • Gareau, TLP, Smith, RG, Barbercheck, ME and Mortensen, DA. 2010. Spider plots: a tool for participatory extension learning. Journal of Extension, 6:33-40.
  • Mirsky, S.B., E. Gallandt, D.A. Mortensen, W.S. Curran and D.L. Shumway. 2010. Reducing the germinable weed seedbank with soil disturbance and cover crops. Weed Research, 50:341-352.
  • Ryan, MR, RG Smith, SB Mirsky, DA Mortensen, and R Seidel. 2010. Management filters and species traits: Weed community assembly in long-term organic and conventional systems. Weed Science 58:265-277.
  • Mortensen, D.A., Rauschert, E.S.J., and A. Nord. 2009. The role of roads in plant invasions. Invasive Plant Science and Management, 2: 191-199. 
  • Dauer, J., E. Luschei, and D.A. Mortensen. September, 2009. Effects of Glyphosate-Resistant Crop Adoption on the Connectivity of a Landscape: An Herbicide-Resistant Weed Perspective. Landscape Ecology, 24: 735-747.
  • Dauer, J., D.A. Mortensen, M. VanGessel, E. Shields. January, 2009. Conyza canadensis seed ascent in the lower atmosphere. Agricultural and Forest Meteorology, 149:526–534.
  • Scott A. Isard, David A. Mortensen, Shelby J. Fleischer and Erick D. De Wolf. 2008. Application of Aerobiology to IPM, pp. 90–106. In Integrated Pest Management Systems. Cambridge Press.
  • Dauer, J., D.A. Mortensen, and M. VanGessel. 2007. Spatial and temporal dynamics governing long distance dispersal of Conyza canadensis. J. Applied Ecology, 44:105–114.
  • Dauer, J., D.A. Mortensen, and R. Humston. 2006. Controlled experiments to predict horseweed (Conyza canadensis) dispersal distances. Weed Science 54:484–489.
  • Burton, M.G., D.A. Mortensen, D.B. Marx, and J.L. Lindquist. 2004. Factors affecting the realized niche of common sunflower (Helianthus annuus) in ridge-tillage corn. Weed Science 52:779–787.
  • Humston, R., D.A. Mortensen, and O.N. Bjørnstad. 2005. Anthropogenic forcing on the spatial dynamics of an agricultural weed: the case of the common sunflower. J. Applied Ecology 42, 863–872.
  • Peskin, N, D.A. Mortensen, B.P. Jones, and M.R. Booher. 2005. Grass-selective herbicides improve diversity of sites infested with Japanese stiltgrass. Ecological Restoration 23, 1–2.
  • Hilgenfeld, K.L., A.R. Martin, D.A. Mortensen, and S.C. Mason. 2004. Weed management in a glyphosate resistant soybean system: weed species shifts (Glycine max). Weed Technology. 18:284–291.
  • Mortensen, D.A., L. Bastiaans and M. Sattin. 2000. The role of ecology in developing weed management systems: an outlook. Weed Research 40:49–62.