Steven G. Hallett
Associate Professor of Weed Science

Purdue University
Botany and Plant Pathology, Lilly Hall
915 West State Street
West Lafayette, IN 47907-2054

Office:  LILY 1-331
Phone:  (765) 494-7649
FAX:      (765) 494-0363
E-mail:   

Area: Weed Science - Biological control of weeds with emphasis on the discovery and development of bioherbicides.

Education

B.Sc. 1987. Lancaster University, UK.
Ph.D. 1991. Lancaster University, UK.

Research Interests

Discovery and Development of Bioherbicides

Weed technology and weed management strategies are continually changing to meet emerging challenges in agriculture. A number of weeds consistently escape, or are unsuited to current weed management technologies, and pressure continues to increase upon the use of certain herbicides due to concerns of adverse environmental and human health impacts. It is important that a diverse array of effective, sustainable, and environmentally benign weed control tools and methodologies remain available to producers.

Weeds, like all plants, are host to a wide range of pathogens. Under natural conditions, these plant pathogens rarely have a dramatic impact, due to limitations of the environment, the host, or the pathogen. Many plant pathogens, however, have the potential to cause dramatic epidemics under optimal or manipulated conditions. The principle of the bioherbicide approach is to release a weed pathogen from the natural regulation that limits its effect, and to develop an artificial epidemic which is sufficiently rapid, damaging and sustained to deliver a desired level of control within a particular production system. The disease epidemic should not cause damage to non-target plants or other organisms, and should decline through time towards its original size under the normal constraints of the environment. Our goal is to develop plant pathogens as products which can be fully integrated into production systems to deliver economic and environmentally safe weed management. Bioherbicides have particularly strong potential to be developed as weed control products for niche markets for which chemical herbicides are unavailable or poorly suited. The cost of developing a bioherbicide is intrinsically much lower than that of a chemical herbicide, and bioherbicides can deliver economic weed control with minimal environmental impact.

Interactions Between Chemical Herbicides and the Candidate Bioherbicide Microsphaeropsis amaranthi on Waterhemp

Waterhemp (Amaranthus tuberculatus) has become a dominant weed of Midwestern corn/soybean in the last decade. The ascendance of waterhemp has been due, in part, to the development of a wide range of biotypes resistant to various herbicides. Of particular concern is the possibility that waterhemp biotypes have developed resistance to glyphosate.

David Smith

David Smith is conducting his MS in this laboratory investigating the response to glyphosate of a range of different populations of waterhemp from Ohio, Indiana, Missouri, Illinois and Iowa. He has shown that there is a range of different responses (Figure 1). Additionally, David is studying the interactions between a candidate bioherbicide fungus, Microspaeropsis amaranthi, and chemical herbicides. He has shown that sub-lethal rates of glyphosate can predispose waterhemp to infection by M. amaranthi (Figure 2).

Figure 1. Clone ALT1 from Altamont, IL shows significant levels of resistance. Plants treated with glyphosate concentrations significantly higher than the recommended rate (1X = 0.63 kg ae/ha) were not killed. Plants treated with the recommended rate were only slightly stunted.

Figure 2. Dry weight of A. tuberculatus treated with glyphosate and Microsphaeropsis amaranthi in a split-application. Bars with the same letter(s) are not significantly different (P=0.05).

Soil Microbial Ecology

Kathy Anderson is using the molecular technique Denaturing Gradient Gel Electrophoresis of PCR-amplified ribosomal RNA genes (PCR-DGGE) to investigate the microbial ecology of weed roots, and the soil that surrounds them.

Kathy Anderson

PCR-DGGE can be used to analyze the composition of microbial communities from DNA extracted directly from the soil. Consequently, the technique can be used to study the large number of species that can not be readily grown in culture. This technique is being used to study the changes in soil microbial communities that occur under different management systems, including different types of tillage, nutrient management and weed management.

Future research will apply this technology to the analysis of the effect of organic vegetable production upon the microbial ecology of soils. Additionally, we anticipate developing research that will apply PCR-DGGE to the analysis of the microbial ecology of crops in developing countries that are infested by the root parasitic weeds Striga (witchweeds) and Orobanche (broomrapes).

This gel represents a preliminary investigation of the microbial ecology of red clover (Trifolium pratense) during parasitism by clover broomrape (Orobanche minor), and demonstrates that different organisms inhabit the rhizosphere of the parasite (O. minor) and the host (T. pratense), even though the two root systems were excavated from the same hole. Each band represents a different species of microbe from the soil sample. Lane M: Marker sequences, Lanes 1-4. Profiles for O. minor rhizosphere soil. Lanes 5-8: Profiles for T. pratense rhizosphere soil. Bands 1-3: Unique to O. minor. Band 4: Unique to T. pratense.

Future Projects

A number of research projects are under development, including:

• Application technology for bioherbicides. This project will involve a detailed analysis of the dynamics of bioherbicide droplets as they as produced by the nozzle tip, travel in-flight and are deposited on the target.
• Understanding the physiological basis of the interaction between glyphosate and Microsphaeropsis amaranthi on waterhemp. This project will investigate the physiological mechanism of predisposition of waterhemp plants to infection by M. amaranthi that is caused by sub-lethal rates of the herbicide glyphosate.

Teaching

Undergraduate

Introductory Weed Science BTNY 304. (Spring Semester only starting in 2004 – co-taught with Dr. Kevin Gibson). Introduction to the biology and ecology, identification and management of weeds.

The Microbial World BTNY 207. (Spring Semester). Everything you wanted to know about microbiology, evolution, beer making, cheese making, AIDS, SARS, West Nile, Mad Cow disease and the meaning of life… but were too afraid to ask. This is a general interest course with no prerequisites, enjoyable for scientists and non-scientists alike, that reveals the microbial world in a new, fun way. All course materials are provided free of charge to each student on CD.

Graduate

A new graduate course is under development for Fall 2004. This course will cover advanced aspects of Weed Biology and Ecology, and will be co-taught with Dr. Kevin Gibson and Dr. Bill Johnson.

Professors in the Classroom

Many of our faculty are willing to come and speak to your high school classes -- free of charge. Below is a talk that I give that can be scheduled by contacting the Professors in the Classroom:

• What is Life? - We can tell a living thing from a non-living thing...right? Maybe it's not so simple. This lecture will discuss the nature of the universe with respect to the earth and its living organisms. Emphasis will be on the origins and the early evolution of life on earth.

Assistantships and Positions

A research assistantship is available for a student wishing to pursue a Masters or PhD. Please contact Steve Hallett directly. A number of different projects related to biocontrol and microbial ecology can be designed. Follow these links for general information on graduate programs or employment announcements.

Selected Publications

Beed, FD, SG Hallett, J Venne & AK Watson. 2007. Biocontrol using Fusarium oxysporum: a critical component of integrated Striga management. In: J Gressel & G Ejeta (eds) Integrating New Technologies for Striga Control: Towards Ending the Witch-Hunt. World Scientific Publ. Co. Inc., Hackensack, NJ.

Callaway, RM, D Cipollini, K Barto, GC Thelen, SG Hallett, D Prati, K Stinson & JN Klironomos. 2007. An invasive plant suppresses fungal mutualisms in America but not in its native Europe. Ecology. In Press.

Davis, AS, KI Anderson, SG Hallett and KA Renner. 2006. Weed seed mortality in soils with contrasting agricultural management histories. Weed Sci. 54:291-297.

Hallett, SG. 2006. Dislocation from coevolved relationships: a unifying theory for plant invasion and naturalization? Weed Sci. 54:282-290.

Smith, DA, DA Doll, D Singh & SG Hallett. 2006. Climatic constraints to the potential of Microsphaeropsis amaranthi as a bioherbicide for common waterhemp. Phytopathology 96:308-312.

Smith, DA & SG Hallett. 2006. Interactions between chemical herbicides and the candidate bioherbicide Microsphaeropsis amaranthi. Weed Sci. 54:532-537.

Smith, DA & SG Hallett. 2006. Variable response of common waterhemp (Amaranthus rudis Sauer) to glyphosate. Weed Technol. 20:466-471.

Stinson, KA, S Campbell, JR Powell, BE Wolfe, RM Callaway, GC Thelen, SG Hallett, D Prati & JN Klironomos. 2006. Invasive plant suppresses the establishment and growth of native trees by allelochemical disruption of belowground mutualists. PLoS Biology 4:727-731.

Doll, DA, PE Sojka & SG Hallett. 2005. Factors affecting the efficacy of spray applications of the bioherbicidal fungus Microsphaeropsis amaranthi. Weed Technol. 19:110-115.

Héraux, FMD, SG Hallett & SC Weller. 2005. Combining Trichoderma virens-inoculated compost and a Rye Cover Crop for Weed Control in Transplanted Vegetables. Biological Control 34:21-26.

Héraux, FMD, SG Hallett & SC Weller. 2005. Composted Chicken Manure as a Medium for the Production and Delivery of Trichoderma virens for Weed Control. Hortscience 40:1394-1397.

Hallett, SG. 2005. Where are the Bioherbicides? Weed Sci. 53:404-415.

Anderson, KI & SG Hallett. 2004. Herbicidal spectrum and activity of Myrothecium verrucaria. Weed Sci. 52:623-627.

Léger, C, SG Hallett & AK Watson. 2001. Performance of Colletotrichum dematium for the control of fireweed (Epilobium angustifolium) improved with formulation. Weed Technol. 15:437-446.

Brière, SC, AK Watson, TC Paulitz & SG Hallett. 2000. Oxalic acid production and mycelial biomass yield of Sclerotinia minor for the formulation enhancement of a granular turf bioherbicide. Biocontrol Sci. Technol. 10: 281-289.

Masangkay, RF, TC Paulitz, SG Hallett & AK Watson. 2000. Characterization of sporulation of Alternaria alternata f. sp. sphenocleae. Biocontrol Sci. Technol. 10:385-397.
                                   
 Masangkay, RF, TC Paulitz, SG Hallett & AK Watson. 2000. Solid substrate production of Alternaria alternata f. sp. sphenocleae Conidia. Biocontrol Sci. Technol. 10:399-409.

Masangkay, RF, TC Paulitz, SG Hallett & AK Watson. 1999. Factors influencing biological control of Sphenoclea zeylanica with Alternaria alternata f.sp. spenocleae. Plant Dis. 83:1019-1024.
    
Yu, X, SG Hallett, J Sheppard & AK Watson. 1998. Effects of carbon concentration and carbon to nitrogen ratio on growth and sporulation of Colletotrichum coccodes in a cyclone column bioreactor. J. Ind. Microbiol. Biotechnol. 20: 333-338.

Yu, X, SG Hallett, J Sheppard & AK Watson. 1997. Application of the Plackett-Burman experimental design to evaluate nutritional requirements for the production of Colletotrichum coccodes spores. Applied Microbiol. Biotechnol. 47:301-305.

Ciotola, M, AK Watson & SG Hallett. 1996. Discovery of an isolate of Fusarium oxysporum with potential to control Striga hermonthica in Africa. Weed Res. 35:303-309.

Diarra. C, M Ciotola, SG Hallett, DE Hess & AK Watson. 1996. Field efficacy of Fusarium oxysporum for the control of Striga hermonthica. Nuisibles Pests Pragas 4:257-263.

DiTommaso, A, AK Watson & SG Hallett. 1996. Infection by the fungal pathogen Colletotrichum coccodes affects velvetleaf (Abutilon theophrasti)-soybean competition in the field. Weed Sci. 44:924-933.

Brière, SC, AK Watson, TC Paulitz & SG Hallett. 1995. First report of a Phoma sp. on common ragweed in North America. Plant Dis. 79:968.

Paul, ND, PG Ayres, & SG Hallett. 1993. Mycoherbicides and other biological control agents for Senecio spp. Pesticide Sci. 37:323-329.

Hallett, SG & PG Ayres. 1992. Invasion of rust (Puccinia lagenophorae) aecia on groundsel (Senecio vulgaris) by secondary parasites: death of host. Mycol. Res. 96: 142-144.

Paul, ND, PG Ayres & SG Hallett. 1992. Making biological herbicides more effective. J. Biol. Educ. 26: 94-99.

Hallett, SG, P Hutchinson, ND Paul & PG Ayres. 1990. Conidial germination of Botrytis cinerea in relation to aeciospores and aecia of groundsel rust (Puccinia lagenophorae). Mycol. Res. 94:603-606.

Hallett, SG, ND Paul & PG Ayres. 1990. Botrytis cinerea kills groundsel (Senecio vulgaris) infected by rust (Puccinia lagenophorae). New Phytol. 114:105-109.