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Steve G Hallett

Horticulture and Landscape Architecture 

  • Associate Professor of Horticulture

Botany and Plant Pathology 

  • Associate Professor
Lilly Hall Room 1-351

In Dr. Hallett's book, Life without Oil, he explains that we must plan for a future without reliance on oil and shift to a new energy future by adopting a wiser, more sustainable stewardship of our natural resources.  View more information on Life without Oil.

Dr. Hallett’s research interests are in the broad area of the ecology of plant pathogen interactions. His applied research targets the development of bioherbicides for weed control and studies the mechanisms of herbicide resistance while his basic research studies the ecology of the interactions between weeds and soil microbial communities in agricultural and natural systems.

The role of the herbicide glyphosate in broad acre agriculture has increased enormously since the development of glyphosate resistant crops. It is a non-selective herbicide that can be used to target nearly all weed species in cropping systems and the advent of glyphosate resistant crops has enabled its use to be expanded to postemergence applications. The use of glyphosate in glyphosate tolerant crops has delivered significant improvements in efficiency in Midwestern farming, and it has been adopted by the majority of corn/soybean growers. In the long term, however, this cropping system is threatened by the evolution of glyphosate tolerant weeds that, should they become widespread, could seriously impede the effectiveness of glyphosate. A number of weeds have already evolved glyphosate – mostly at low levels – indicating that the threat is real. Importantly, however, except for a few exceptions, we do not know how this resistance has evolved. The resistance mechanisms that have been elucidated in weeds that have evolved resistance to other herbicides do not adequately explain resistance to glyphosate. Dr. Hallett, Dr. G. Johal (BTNY) and Dr. Johnson (BTNY) hypothesize that the role of plant defense mechanisms and soil microorganisms may have been overlooked. We know, from the research of Dr. Johal and others, that soil borne fungal plant pathogens play an important role in the activity of glyphosate. The site of action of glyphosate is an enzyme in the shikimic acid pathway that synthesizes the aromatic amino acids, and the conventional wisdom is that glyphosate kills plants by starving them of amino acid substrates for protein synthesis. Rather than being killed simply by the lack of aromatic amino acids, however, plants are actually killed, before protein starvation, by pathogens. Pathogens, then, should be considered an integral part of the mode of action of glyphosate. We thus hypothesize that this microbe mediated mechanism may be the source of glyphosate resistance. Resistant plants, rather than evolving a mechanism to resist glyphosate per se may evolve a mechanism to resist the pathogens that take advantage of glyphosate-weakened plants. Jessica Schafer has recently been hired as a graduate student to test this hypothesis, using, as models, populations of marestail (Conyza canadensis), lamsquarters (Chenopodium album) and giant ragweed (Ambrosia trifida) assayed as glyphosate resistant by Dr. Johnson’s lab.

Awards & Honors

(2012) BTNY Outstanding Teaching Award. Department of Botany and Plant Pathology.

(2010) Outstanding Undergraduate Teacher and Advisor. Department of Botany & Plant Pathology, Purdue University.

(2002) "Award of Excellence". Weed Science Society of America.

Selected Publications

Hallett, S. G. (2013). The Efficiency Trap (Vol. 1). Amherst, New York: Prometheus Books.

Hallett, S. G., & Wright, J. (2011). Life Without Oil (Vol. 1). Amherst, New York: Prometheus Books.

Schafer, J. R., Hallett, S. G., & Johnson, W. G. (2012). Soil microbial root colonization of glyphosate-treated giant ragweed (Ambrosia trifida), horseweed (Conyza canadensis), and common lambsquarter (Chenopodium album) biotypes to glyphosate in the presence and absence of soil microoorganisms. Weed Science, 60, 641-650.

Schafer, J. R., Hallett, S. G., & Johnson, W. G. (2012). Response of giant ragweed (Ambrosia trifida), horseweed (Conyza canadensis), and common lambsquarters (Chenopodium album) biotypes to glyphosate in the presence and absence of soil microorganisms. Weed Science, 60, 641-649.

Hallett, S. G., Shabana, Y., Singh, D., & Ortiz-Ribbing, L. M. (2010). Production and formulation of high quality conidia of Microsphaeropsis amaranthi for the biological control of weedy Amaranthus species. Biological Control, 55, 49-57.

Callaway, R. M., Cipollini, D., Barto, K., Thelen, G. C., Hallett, S. G., Prati, D., . . . Klironomos, J. N. (2008). An invasive plant suppresses fungal mutualisms in America but not in its native Europe. Ecology, 89, 1043-1055.

Smith, D. A., Doll, D. A., Singh, D., & Hallett, S. G. (2006). Climatic constraints to the potential of Microsphaeropsis amaranthi as a bioherbicide for common waterhemp. Phytopathology, 96, 308-312.

Hallett, S. G. (2006). Dislocation from coevolved relationships: a unifying theory for plant invasion and naturalization?. Weed Science, 54, 282-290.

Stinson, K., Campbell, S., Powell, J. R., Wolfe, B. E., Callaway, R. M., Thelen, G. C., . . . Klironomos, J. N. (2006). Invasive plant suppresses the establishment and growth of native trees by allelochemical disruption of belowground mutualists. PLoS Biology, 4, 727-731.