Education
Ph.D.,
Agronomy, 1994, University of Arkansas
Dissertation topic: Dissipation of selected pesticides in the water
and soil of flooded rice culture
M.S., Agronomy, 1989, University of Arkansas
Thesis topic: Johnsongrass control and rhizome carbohydrate reduction
with postemergence herbicides
B.S., Agricultural Science, 1987, Western Illinois University
Background
2005-present, Associate Professor of Weed Science, Purdue University, West Lafayette, IN
2002-2005,
Assistant Professor of Weed Science, Purdue University, West Lafayette,
IN
1998-2002,
Assistant Professor of Agronomy, University of Missouri-Columbia
1995-1998, Extension Assistant Professor of Agronomy, University of
Missouri-Columbia
1994-1995, Research Scientist, Land O'Lakes, Inc., Webster City, IA
Research
and Extension Interests
Rationale
The estimated average monetary loss caused by weeds in field crops
grown in the U.S. is over 4 billion dollars each year. Weed management
expenses are one of the largest variable costs incurred by growers
annually. Weeds growing on cropland are like crop plants themselves,
drawing upon the soil and air for essential elements. Unfortunately,
weeds obtain essential elements at the expense of adjacent crop plants.
The result of inadequate weed control is a reduction of crop yield
and quality. Traditionally, weed management practices have included
preventative, cultural, mechanical, biological, and chemical tactics.
However, with the rapid increase in the number of effective herbicides
in the 1960-1990's, weed management techniques have become more reliant
on herbicides in the last 20 years. In any biological system, strong
dependence on any single tactic results in selection pressure for species
(weeds, insects, and/or diseases) which can exploit the niche left
by the single tactic. As a result of overdependence on herbicides,
the number of herbicide-resistant weeds has grown from less than 10
in the 1960's to over 200 in 2002. Additionally, there are over 1000
non-indigenous plant species which can potentially infest crop production
systems if given the opportunity. Therefore, production of food for
humans and livestock and the economic well being of Indiana farmers
depends heavily on effective, integrated management of weeds and other
plant pests.
My Program Objectives
- Develop weed management systems that are economically and environmentally
sound, integrate cultural practices with judicious herbicide use,
improve efficiency of production, and minimize selection pressure
for herbicide-resistant weeds.
- Promote grower acceptance of these weed management systems through
education efforts targeting growers, crop consultants, input suppliers,
industry representatives and extension educators in Indiana and
surrounding states.
To that end, my Extension and Research efforts are focused on the following topics:
Biology,
Management and Distribution of Glyphosate Resistant Horseweed (Conyza
canadensis), and other Weeds
Production of Roundup Ready soybeans and utilization of no-till practices relies
on extensive use of the herbicide glyphosate (Roundup). In 2003 more than 90%
of soybean acres in Indiana were planted with Roundup Ready varieties and no-till
production practices were utilized on 60% of the soybean acres. However, adoption
of no-till practices and increased reliance on glyphosate has resulted in a serious
concern for long-term use of this valuable weed management tool.
Glyphosate-resistant field bindweed was first reported in the 1980’s by Dr.
Steve Weller at Purdue. Since 1998, a number of other species resistant to
glyphosate have been reported in situations where repeated applications have
occurred. Glyphosate resistant horseweed (a.k.a. marestail) was discovered in
2002 at a few sites in southeast Indiana and southwest Ohio. This issue is significant
because the weed has the ability to germinate in the fall, spring or summer and
it’s seed is easily moved by wind, facilitating spread across a large agricultural
region. In addition, horseweed is naturally tolerant of many herbicides and resistance
has been reported for many of our best alternatives to glyphosate. Horseweed
can potentially impact soybean yield quite dramatically due to season-long competition.
Tillage temporarily eliminates the threat of horseweed, but must be repeated
to prevent reinfestation. Widespread return to intensive tillage would negatively
impact crop production efficiency and could reverse productivity and environmental
gains.
Current efforts are designed to 1) assess the current distribution of glyphosate-resistant
horseweed in cropped and non-cropped areas, 2) evaluate the biology, management,
and fitness of herbicide-resistant horseweed, and problematic populations of
common lambsquarter and giant ragweed so producers can minimize the impact of
these weeds on their operation and the environment, and 3) determine if the presence
of glyphosate-resistant horseweed can be used as an indicator species for other
weed with enhanced tolerance to glyphosate. We are working closely with Dr.
Kevin Gibson, and Dr. Steve Weller at Purdue, Dr. Mark Loux and Mr.
Jeff Stachler at The Ohio State University and Dr. Pat Tranel at the University
of Illinois in this research.
Mr. Vince Davis, Weed Science Research Associate is coordinating much of the
effort to assess the distribution of this glyphosate-resistant horseweed in Indiana.
He has conducted an extensive survey of 16 counties each in the fall of 2003,
2004, and 2005 and collected samples from over 500 sites that have been screened
for tolerance to glyphosate in the greenhouse. His M.S. research (completed in
2006) was focused on gaining a better understanding of horseweed emergence, survival
rates, growth, seed production, and effective management practices. His Ph.D.
research will focus gaining a better understanding of the fitness and genetics
of glyphosate-resistant biotypes. The results of our projects can be viewed on
our recently developed website
devoted just to our efforts on horseweed.
Mr. Greg
Kruger, a Ph.D. student, is conducting studies on the biology and
fitness of 2,4-D tolerant horseweed and horseweed competition in
soybean. Through our sampling and screening efforts mentioned
above, we have identified a number of populations that show tolerance
not only to glyphosate, but also to some ALS inhibitors such as Classic
and FirstRate, and to 2,4-D. Greg is screening all of our horseweed
populations to find those with enhanced tolerance to ALS inhibitors
and 2,4-D, and will be determining if any fitness penalties are associated
with 2,4-D tolerance in horseweed.
Mr.
Andy Westhoven, a M.S. student, is conducting studies on the biology
and management of common lambsquarter and giant ragweed populations
that have become more difficult to control in Roundup Ready soybeans. Our
horseweed survey efforts mentioned above have provided us with an extensive
database of known locations of glyphosate resistant horseweed and the
late-season prevalence of other weed species when the horseweed samples
were collected. Andy will be using this database to determine if glyphosate-resistant
horseweed can be used as an indicator species for fields that contain
other weeds with enhanced tolerance to glyphosate. Andy has returned
to dozens of sites to collect common lambsquarter and giant ragweed
seed from locations known to have glyphosate-resistant marestail. These
populations are being screened in the greenhouse and in the field to determine
their tolerance to glyphosate compared to known sensitive populations. Andy
is also conducting in-field management studies in grower fields to evaluate various
management tactics for fields that have problematic common lambsquarter and giant
ragweed populations. We are working closely with Dr. Mark Loux and Mr.
Jeff Stachler at The Ohio State University on these research projects.
Interactions
Between Winter Annual Weeds and Soybean Cyst Nematode
Soybean cyst nematode (SCN) is a viable threat to profitable soybean production
in the Indiana and the entire Midwest. Winter annual weed populations in production
fields have been increasing due to the widespread adoption of conservation tillage
practices and reduced reliance on herbicides with soil residual activity. Among
the many negative impacts of winter annual weeds is that a number of these species
can serve as alternate hosts for SCN. Current integrated pest management (IPM)
systems for SCN include rotation to a non-host crop and use of SCN resistant
soybean varieties. However, these management recommendations may be inadequate
if SCN is able to reproduce on winter annual weeds when soybean is not present.
Our specific objectives are to (1) determine the level of infestation of winter
annual weeds in fields known to be infested with SCN and document the association
of SCN with these winter annuals, (2) determine the temperature requirements
under which SCN juveniles can survive and reproduce in the roots of winter annual
weed hosts, and (3) determine the influence of winter annual weed management
practices and crop rotation on weed and SCN population density. We are collaborating
with Dr. Andreas
Westphal, Dr. Virginia Ferris, and Dr. Jamal Faghihi at Purdue and
Dr. Bryan Young at Southern Illinois University, and Dr. Kent Harrison at The
Ohio State University in this research.
Mr. Earl Creech, a Ph.D student, has initiated long-term field studies to evaluate
the influence of winter weed management tactics and crop rotations on winter
weed and SCN population densities. Earl has also surveying crop production fields
throughout Indiana to document the degree to which winter annual weeds infest
fields with SCN. Lab and growth chamber studies were conducted to assess the
influence of various environmental conditions and winter weed population densities
and species mixtures on SCN population dynamics.
Ms. Valerie Mock, a M.S. student is conducting studies to evaluate the effect
of fall purple deadnettle and volunteer soybean control timing on winter weed
seed and biomass production, and SCN population densities. Valerie has also conducted
greenhouse studies to evaluate the interactive effects of soybean, purple deadnettle
and rye, a plant known to suppress SCN egg hatch, on SCN population densities
and the competitive effects of the plants on each other.
For more information on winter weeds and SCN, see our recently launched
website on this topic (http://www.btny.purdue.edu/weedscience/SCN/).
Management of Weeds Common to No-Till Systems
It is well documented that no-tillage crop production practices provide many
financial and environmental benefits. However, no-tillage systems allow a unique
complex of weeds to develop. Dense infestations of certain weeds can negatively
influence spring soil characteristics and overall field productivity. Weeds of
specific interest include chickweed, because of it’s wide-spread distribution
in Indiana, glyphosate-resistant horseweed (mentioned earlier), purple deadnettle
and henbit because of their ability to serve as hosts for SCN, and the perennial
weed common dandelion, because of it’s ability to interfere with planting
and crop emergence, and lack of in-crop tools for it’s control, and common
lambsquarter and giant ragweed, because of their long-term problematic nature
and recent problems with poor control in Roundup Ready soybeans.
Our goals are to determine 1) the influence of in-crop, residual herbicide use
on winter annual weed emergence after crop harvest, 2) the effectiveness of fall
and spring applied herbicides on winter annual and perennial weeds, and 3) management
systems for control of summer annual and perennials in no-till systems. Field
research studies are conducted at the Agronomy Center for Research and Education
(ACRE) Pinney Purdue Agricultural Center (PPAC), SEPAC, Throckmorton Purcue Agricultural
Center (TPAC) and in farmer-cooperator fields in selected locations in Indiana.
The objective in each of these experiments is to evaluate various management
systems on the early-season and in-crop control of specific weed species. Much
of the work to manage my field research program falls on the shoulders of Mr.
Vince Davis and Mr. Kevin Westerfeld, both of whom are Weed Science Research
Associates in my program. The results of most of the general field experiments
we have conducted, dating back to 2003, can be found at the Integrated
Weed Management Research Website.
Extension and Outreach Efforts
Many growers receive the bulk of their crop management information from crop
consultants, agrichemical dealers, and Extension educators. These individuals
receive their information from campus-based University Extension. The Extension
Weed Science Team of Mr. Glenn Nice, Dr.
Tom Bauman, and Dr. Bill Johnson have collaborated on developing both traditional
and electronic weed management information for these clientele. Information from
Dr. Johnson’s research program is incorporated into these informational
pieces as it becomes available.
Purdue Weed Science Website -
Contains frequently updated newsworthy articles for agronomic crops,
horticulture crops, turf and lawn, and other general items of interest.
Also contains links to sites on weed identification, herbicide injury,
weed science faculty, staff and students at Purdue, and weed management
tools from Purdue and other Universities.
Indiana Select-A-Herb Website - This
web-based tool provides herbicide response ratings for weeds in various
cropping systems. The database is an accumulation of weed control ratings
from several Midwest sources and allows the user to use drop down menu’s
to find herbicides that provide good to excellent control of over 200
weeds in 15 crops.
WeedSOFT for Indiana -
WeedSOFT® is a decision support system designed to assist growers,
consultants, and extension agents in making both proactive and reactive
weed management decisions. WeedSOFT® provides the treatment information
needed according to specific field conditions while factoring in economic
and environmental principles.
Integrated
Weed Management Research Website -
This site contains field research reports on burndown and in-season
management of the most common agronomic weeds in Indiana corn,
soybean, wheat, alfalfa, and grass pastures.
Weed
Control Guide for Ohio and Indiana (WS16) –We have
collaborated with Extension Weed Scientists at The Ohio State University
to produce a single guide for both states. This guide contains over
150 pages of information on weed management tactics in corn, soybean,
grain sorghum, wheat, alfalfa, and grass pastures. It is available
on the web and in print from the Ohio State Media Distribution, 385
Kottman Hall, 2021 Coffey Rd., Columbus, Ohio 43210-1044, phone: 614-292-1607,
fax: 614-292-1248, pubs@ag.osu.edu
Weeds to Watch Poster – (pdf
file) Weed communities continually shift in response to management
practices. The weeds included on this poster pose in increasing threat
to agronomic fields. The poster also contains maps that provide information
regarding current distribution of each species in Illinois, Indiana,
Iowa, Minnesota, Wisconsin and Michigan.
Welcome to the Home of Horseweed - Horseweed
(Conyza canadensis) a.k.a. marestail, presents
serious problems for no-tillage glyphosate resistant soybean production
in several states including Indiana, Ohio, and Illinois. We have
developed a website specifically devoted to our efforts to study
the distribution, biology and management of horseweed.
Winter
Annual Weed and SCN Management -
This website provides the latest research findings and management
recommendations regarding the interaction of SCN and winter annual
weeds.
Assistantships
and Positions
| Description of duties |
The successful candidate will conduct greenhouse,
lab, and field research to evaluate potential genetic, biochemical
and physiological mechanisms of glyphosate resistance in giant
ragweed biotypes. Additional studies may include investigations
of fitness of resistant biotypes and gene flow. The candidate will
also be involved in all aspects of field and greenhouse research,
grant proposal and report writing, presentations at field days
and student teaching. |
| Qualifications sought |
M.S. in Weed Science, Agronomy, Plant Biology, or a related area.
Experience in plant physiology or herbicide uptake/translocation
research would be beneficial, but not required. Individual must
be able to work independently and have excellent time management,
planning, interpersonal, written, and verbal communication skills.
Must be willing and able to work with pesticides and outdoors in
adverse environmental conditions. |
| Contact for additional
information |
Please contact Bill Johnson or Steve Weller if you have specific
questions about the position or responsibilities.
Bill Johnson
telephone: 765 494 4656
email: wgj@purdue.edu
or
Steve Weller
telephone: 765 494 1333
email: weller@purdue.edu |
| Application procedure |
All
interested applicants must apply online at http://www.gradschool.purdue.edu.
Follow the ADMISSIONS link to the online application. Applicant
must apply to Purdue University's Graduate School and designate
Botany & Plant Pathology as department of choice. No paper
applications will be accepted. |
Please
contact me directly for information on assistantships and openings
in my program. Follow these links for general information on graduate
programs or employment announcements.
Selected
Publications
Recent Significant Publications:
Davis, V. M., K. D. Gibson, T. T. Bauman, S. C. Weller, and W.
G. Johnson. Influence of weed management practices and crop
rotation on glyphosate-resistant horseweed population dynamics and
crop yield. Weed Sci. (in press).
Creech, J. E., J. Faghihi, V. R. Ferris, A. Westphal, and W.G. Johnson.
Influence of intraspecific henbit (Lamium amplexicaule) and purple deadnettle
(Lamium purpureum) competition on soybean cyst nematode (Heterodera
glycines) reproduction. Weed Sci. (in press).
Johnson, W. G., E. J. Ott, K. D. Gibson, R. L. Nielsen, and
T. T. Bauman. Influence of nitrogen application timing on the effects of low
density giant ragweed (Ambrosia trifida L.) interference in corn (Zea
mays L.). Weed Technol. (in press).
Creech, J. E., J. Faghihi, V. R. Ferris, and W. G. Johnson.
Survey of Indiana producers and crop advisors: A perspective on winter annual
weeds and soybean cyst nematode (Heterodera glycines). Weed Technol.
(in press).
Ott, E. J. C. K. Gerber, D. B. Harder, C. L. Sprague, and W. G. Johnson. Prevalence
and influence of stalk boring insects on glyphosate activity on Indiana and Michigan
giant ragweed (Ambrosia trifida). Weed Technol. (in press).
Johnson, W. G., K. D. Gibson, and S.P. Conley. Does weed size
really matter? An Indiana grower perspective about weed control timing. Weed
Technol. (in press).
Harder, D. B., C. L. Sprague*, C. D. Difonzo, K. A. Renner, E. J. Ott, and W.
G. Johnson. 2007. Influence of stem boring insects on common lambsquarters
(Chenopodium album) control in soybean with glyphosate. Weed Technol.
21:241-248.
Knezevic, S., W. G. Johnson, and C. L. Sprague. 2007.
WeedSOFT: Effects of corn row spacing for predicting herbicide efficacy on selected
weed species. Weed Technol. 21:219-224.
Nelson, K. A., W. G. Johnson, J. D. Wait, and R. S. Smoot. 2006.
Winter annual weed management in corn (Zea mays) and soybean (Glycine
max) and the impact on soybean cyst nematode (Heterodera glycines)
egg population densities. Weed Technol. 20:965-970.
Creech, J. E. and W. G. Johnson. 2006. Survey of broadleaf winter
weeds in Indiana production fields infested with soybean cyst nematode. Weed
Technol. 20:1066-1075.
Gibson, K. D., and W. G. Johnson. 2006. Farmer perceptions of
weed problems in corn and soybean rotation systems. Weed Technol. 20:751-755.
Johnson, W. G. and K. D. Gibson. 2006. Glyphosate resistant weeds and
resistance management strategies: An Indiana grower perspective. Weed Technol.
20:768-772.
Creech, J.E., W. G. Johnson, J. Faghihi, V. Ferris, and A. Westphal.
2005. First report of soybean cyst nematode reproduction on purple deadnettle
under field conditions. Online. Crop Management doi:10.1094/CM-2005-0715-01-BR.
Web
Links of Interest
Purdue
University Weed Science Website http://www.btny.purdue.edu/weedscience
North
Central Weed Science Society http://www.ncwss.org
Weed Science Society of America http://www.wssa.net/
American Society of Agronomy http://www.agronomy.org/
|
Faculty