DEVELOPING BIOLOGICAL / ECOLOGICAL KNOWLEDGE
FOR ENHANCING WEED MANAGEMENT SYSTEMS
Lead Scientist: Joanne
Martin M. Williams II
Management of weeds is essential
for successful crop production. In the U.S. Corn Belt, the primary
method for control of weeds involves the use of herbicides.
Over 95% of the acreage is treated each year with herbicides.
A substantial portion of the acreage is treated with combinations
of herbicides, applied either together or sequentially. Repeat
applications of herbicides are common. The acreage of no-till
production is increasing and the use of postemergence cultivation
is decreasing, resulting in further reliance on herbicides for
control. Under these conditions, herbicides may sometimes be
used when not needed economically and the herbicides in use
may contribute on some occasions to off-target drift and to
environmental contamination. The database regarding weed biology
(germination, emergence, competition, seed production and longevity,
etc.) is not adequate and more work is needed. The weed spectrum
in many fields is shifting from species sensitive to commonly
used herbicides to ones that are somewhat tolerant of these
herbicides and practices being used. Weed biotypes that are
resistant to some classes of herbicides are evolving and are
becoming predominant in some areas.
We are conducting research on
weed biology to enhance the database, with emphasis on the most
troublesome weeds now and anticipated in the future. We believe
these data will help to plan improved and more efficient weed
management systems. Other work is aimed at optimizing the application
and use of new and standard herbicides and combinations in a
systems approach. Our investigations include research on the
distribution, mechanism of resistance, and development of strategies
for managing herbicide resistant weed biotypes and other hard-to-control
species, with emphasis on conservation tillage systems.
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Highlights of Recent
Postemergence applied herbicides
often vary in effectiveness with weather and growth stage of
crop and weeds, but can be made more consistent with the use
of adjuvants. Our fundamental and applied research with adjuvants
helped to explain the role of adjuvants in improving herbicide
efficacy, and showed ways for improving application techniques
to improve weed management with less herbicides inputs.
In regional cooperative work,
we researched hemp dogbane, an important, and hard-to-control
perennial weed in the Corn Belt, and described the biology of
biotypes of this species from several areas. Other studies investigated
the efficacy and fate of several herbicides in this species
and found improved means of management
Soil-applied herbicides vary in
effectiveness depending on soils and weather, among other things.
We conducted cooperative research in normal rainfall situations,
in rainout shelters, and in the greenhouse to assess the optimum
amounts and timing of rainfall needs after application for improved
performance with a variety of herbicides. These results allowed
for improved guidelines for more effective use of these herbicides.
Cooperative work on the chloroacetamide
herbicides helped to define their relative persistence and need
for rainfall, and provided guidelines for time of application
for optimizing their effectiveness and reducing potential for
Regional cooperative research
resulted in our weed emergence data being incorporated into
an area-wide database for generating a mechanistic model of
weed seedling emergence timing in the Corn Belt. These results
are helpful in planning integrated weed management systems.
A series of studies described
the comparative uptake and translocation of various postemergence
applied herbicides and related the results to effectiveness
of control with these herbicides.
Field experiments over several
years determined emergence patterns, seed longevity and seed
production for several of the more troublesome weeds infesting
corn and soybean crops.
Several experiments were conducted
to determine and fine-tune the role of herbicide resistant cropping
systems in weed management and provided guidelines as to the
most appropriate use of these systems, especially with regard
to tillage, row spacing, timing of applications as related to
effectiveness and competition, and combinations with other herbicides.
Cooperative studies with University
of Illinois scientists investigated the crop injury and weed
control of new herbicides, combinations and adjuvants, over
several years and locations. The combined database allows for
the improved selection of herbicides that are more environmentally
benign, have shorter residual, are effective on selected weeds
not controlled by standard herbicides, and often allow for more
effective mixtures that are more consistent and often allow
for reduced herbicide inputs.
In a series of cooperative studies
over several years, we conducted considerable field and greenhouse
research on the Amaranthus complex of weeds, resulting in a
number of reports on identification of the various species,
identification and confirmation of herbicide resistant biotypes,
determination of the mechanism of action, and development of
strategies for improved management. An in vivo method was developed
for assaying plants for the ALS enzyme activity, thus facilitating
determination of herbicide resistance in weed to ALS-inhibiting
herbicides. In other studies, we found that various biotypes
of Amaranthus species showed resistance and cross resistance
to selected herbicides. Improved management strategies were
developed for resistant biotypes, with special emphasis on common
waterhemp, using combinations of chemical and non-chemical control.
We cooperatively located , identified, determined mechanism
of resistance of a common waterhemp biotype that has evolved
multiple resistance to two different classes of herbicides.
Another cooperative study also found biotypes of the weed kochia
that had evolved multiple resistance.
In a 3-year field study, we investigated
the efficacy and economic viability of using ultra low rates
(ULR) of herbicides for weed suppression in corn and soybeans.
The ULR system suppressed weeds enough to allow economical soybean
production all three years of the study but this system proved
viable only during the wettest year for corn.
The herbicide sulfentrazone is
relatively new and can provide excellent control of some of
the waterhemp biotypes resistant to other types of herbicides.
On some occasions, however, it can produce undesirable injury
to soybeans. In a series of greenhouse and field studies, we
worked with this herbicide and a newer, related herbicide, flumioxazin,
to determine if variety differences could be causing some of
the injury noted. Our findings show considerable variety difference
in response to both of these herbicides, but also show in field
trials that at normal use rates, soybean yields will not likely
be reduced. Sulfentrazone was shown to cause more injury at
normal use rates than did flumioxazin.
We conducted cooperative research
to be able to predict absorption, translocation and activity
of foliar applied pesticides in order to enhance pesticide efficacy
and to aid in the development of new products that have desired
biological properties that will allow expression of maximum
activity without adverse environmental consequences. A computer
simulation model was developed and validated that combines and
describes all of the processes of pesticide absorption into
the leaf, transport within the plant and allocation throughout
the plant and predicts how the pesticide will be distributed
in the plant following foliar application. This model should
be useful to researchers in the public and private sectors that
develop and design pesticides for maximum biological activity
and want to understand all the ramifications for weed management.
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Under our current project plan,
our research is aimed toward providing improved knowledge regarding
weeds and their interaction with crop plants. This information
should help in our attempt to develop improved and more environmentally
friendly and cost effective weed management systems, based on
decision aids and improved integrated use of non-chemical means
of management in combination with judicious use of new and standard
herbicides and combinations as appropriate. Other research is
directed toward improving our knowledge and database regarding
the fundamental biology of weeds so that possible weaknesses
in their life cycle can be exploited in developing more environmentally
friendly and sustainable weed management systems.
In the meantime, we are focusing
on continuing some current new research and beginning new preliminary
research in several areas, including the following, most of
which are cooperative with University of Illinois and with other
ARS scientists. Overall goals of these projects include: 1)
collecting fundamental data regarding the biology and ecology
of current and potentially troublesome weeds, including work
on seed banks, emergence patterns, biotype variation and competitive
relationships, 2) researching new herbicides and combinations
with the aim of finding improved weed management with reduced
herbicide inputs and more effective and efficient results, 3)
establishing cooperative research on biocontrol of selected
troublesome weeds in crop and non-crop situations, including
microbial effects on invasive and troublesome weeds, 4) investigating
current and new biotypes of weeds that evolve resistance to
one or more classes of herbicides, 5) investigating the potential
for the use of remote sensing to map weed populations and herbicide
injury, and 6) researching systems for weed management that
include chemical and non-chemical means of control, herbicide
by disease and insect interactions, and optimization of herbicide
resistant cropping systems, with emphasis on conservation tillage,
that aim toward minimizing undesirable effects of herbicides,
reduction of herbicide use, and economical weed management.
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