- B.L. Frick, Southwestern Ontario Agricultural Research Corporation (SWOARC), Harrow, Ontario
Evaluation Summary (Tech. Transfer Report Summaries)
View / Download Final Report [174 KB pdf]
Associated SWEEP/LSP Research
Completed: September, 1990
corn, soybeans, winter wheat, no-till, survey, weed species, weed density,
conventional tillage, conservation tillage, herbicide, inter-row cultivation
Conservation tillage systems have been advocated as a means of reducing
soil erosion and phosphorous run-off from cropland, and of maintaining long-term
soil productivity. Conservation tillage has been defined as any method of
tillage which leaves a minimum of 30% residue on the soil surface. Such
systems range from strict no-till to chisel plowing, but all involve a reduced
frequency of tillage and/or a different type of tillage compared to conventional
systems. One of the main obstacles to widespread adoption of conservation
tillage is the perception by farmers that new and exacerbated weed problems
will occur when tillage is no longer available as a method of weed control.
To address this concern a study was undertaken to determine what weed problems
resulted from a reduction in tillage, and to examine possible management
strategies to handle these problems.
A survey was conducted to examine weed species composition and weed density
in 593 farm fields across southwestern Ontario in 1988 and 1989. The crops
selected for the survey were corn, soybeans and winter wheat. Tillage systems
were categorized as conventional (including some form of soil inversion
as by a moldboard plow), conservation (including some soil disturbance other
than inversion), and no-till (no tillage between the current and previous
crop). Fields were also grouped according to the length of time that a given
tillage system had been practiced.
In general, the same weed species were found in all tillage systems,
but their frequency of occurrence and density varied slightly. All three
tillage types were dominated by five weed species that occurred in more
than 25% of fields: green foxtail, lamb's-quarters, redroot pigweed, common
ragweed, and quack grass. Dandelions also occurred in more than 25% of conservation
and no-till fields, as opposed to 21% of conventional fields. No-till and
conservation tillage fields had higher overall weed densities than conventional
fields. Weed populations varied greatly within tillage systems.
Only a few trends with length of time in a tillage system were observed.
First year conservation tillage fields generally had more green foxtail
and dandelions than conventional fields, but these weeds decreased once
conservation tillage was established. Quack grass decreased in frequency
and density with time in no-till or conservation tillage. Established no-till
and conservation fields had markedly less quack grass than conventional
Reduced tillage systems present an altered environment for weed growth
and so may affect the rate of development of weed species. Most weed control
practices are targeted at particular growth stages. The growth and development
of the more common weed species were monitored in a small subset of the
surveyed fields in 1989. Lamb's-quarters, redroot pigweed, and velvetleaf
showed no difference in the timing of various growth stages among tillage
systems. Green foxtail and common ragweed emerged later in no-till than
in conventional tillage, and so may have been more likely to escape control.
Perennial species emerged at about the same time in all tillages, but grew
more slowly in conventional tillage than in no-till. Dandelion was the only
weed to show a difference in flowering in relation to tillage. Dandelions
flowered most often in no-till fields and least often in conventional fields.
Herbicide-use patterns did not vary substantially among tillage systems,
other than the increased use of burndown treatments, and decreased use of
soil-incorporated chemicals in no-till. The literature on herbicide efficacy
in reduced tillage systems is not conclusive. The primary concerns of farmers
in the study were (1) lack of information on dandelion control, and (2)
the limited number of herbicides registered for burndown applications.
Greenhouse experiments were conducted to determine the effects of simulated
"tillage" treatments on the survival of seeds, vegetative propagules, and
actively growing plants of the more common weed species. Burial of weed
seeds in the autumn, as through plowing, favoured annuals over perennials.
Overwinter survival of roots and rhizomes of perennial species was decreased
if they were brought to the surface. Mechanical damage to the roots of actively
growing annual weeds was an effective control method at all growth stages.
Perennial species were susceptible to mechanical damage only over relatively
short periods of time.
The results presented here show that problem weed species were not substantially
different in different tillage systems. Weed communities were influenced
by geographic region, soil type, field history and level of management,
in addition to tillage. It is probably not appropriate to design a single
strategy for weed management in reduced tillage systems.
The perception that weed management is more difficult in reduced tillage
needs to be challenged. Changes in weed communities are small. Some changes
offer a greater challenge for weed control; other changes offer opportunities
for improved weed control. The transition to conservation tillage or no-till
however may initially require more intensive weed management.
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)
The objectives of the study were:
A total of 593 fields of corn, soybeans and winter wheat in southwestern
Ontario were surveyed in 1988 and 1989. The three tillage systems surveyed
were conventional, conservation (minimum) and no-till.
- to determine the weed species likely to be the greatest problem under
various conservation tillage systems, and to see if their stages of growth
differ between tillage systems.
- to examine the susceptibility of problem weeds to control by herbicide
and tillage methods available in conservation tillage systems.
- to recommend weed management strategies for field testing.
The same weed species were found in all tillage systems, but there was
a slight variation in their frequency of occurrence and density. The weed
species that occurred most frequently in all tillage systems were green
foxtail, lamb's-quarters, redroot pigweed, common ragweed, quackgrass and
dandelions. No-till and conservation tillage fields had higher overall weed
densities than conventional fields. Quackgrass and dandelions decreased
in frequency and density with time in no-till or conservation tillage.
Lamb's-quarters, redroot pigweed and velvetleaf were at similar growth
stages in each tillage system. Green foxtail and common ragweed emerged
later in no-till than conventional. Perennials emerged at about the same
time in all systems, but grew more slowly in conventional tillage than in
no-till. Dandelions flowered most often in no-till fields and least often
in conventional fields.
The increased use of burndown treatments and decreased use of soil incorporated
herbicides were the only differences in herbicide use between tillage systems.
Autumn burial generally decreased the survival of seeds of perennial species
but not of seeds of annual species. Roots of perennial weeds had a lower
survival rate when brought to the surface in the fall versus fall burial.
Laboratory work was conducted to simulate depth of seed germination and
mechanical methods of weed control. Increased seed depth decreased annual
seed germination, however increased the survival of some perennial weeds.
All mechanical damage treatments reduced survival of annuals compared to
undisturbed plants. Reduction of survival rates was more pronounced with
shallow cutting or inversion than with deep cutting. For perennials shallow
cutting or inversion treatments were most effective 3 to 4 weeks after planting.
This seemed to be related to depletion of root reserves used for top growth
that weakened the plants. Simulated inter-row cultivation was an effective
control method for annual weeds but had only a short term effect on perennials.
In general weed species were not substantially different in different tillage
systems and, therefore weed control should not be any more difficult in
reduced tillage systems.
The survey showed only slight differences between tillage systems. In other
field studies shifts toward more perennials and fewer annual weeds have
been observed in no-till. Many experienced farmers report that weed control
is not any more difficult and in fact may be easier than conventional systems.
The study did agree with that observation. The lab studies could use some
field data to back up the results.
- SWEEP Report #19A - Weeds of Corn, Soybean
and Winter Wheat Fields Under Conventional, Conservation and No-Till Management
Systems in 1988 and 1989
- SWEEP Report #32 - Optimal Herbicide Use in
Conservation Tillage Systems
- SWEEP Report #48 - The Feasibility of Band
Spray Application in Conjunction with Inter-Row Cultivation in No-Till Corn
Future Research: ( ) indicates reviewers suggestion for
priority, A - high, C - low.
(C) Conduct field studies of the lab work.
Thursday, May 19, 2011 02:01:00 PM