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SWEEP Report #19a

Weeds of Corn, Soybean, and Winter Wheat Fields Under Conventional, Conservation, and No-Till Management Systems in Southwestern Ontario - 1988 and 1989

(Weed Survey Series Publication 90-1, Agriculture Canada).
[Also called: Appendix 1-4: Studies on the Control of Problem Weed Species in Conservation Tillage Systems (completed September 1990)]

Frick, B., Crop Development Centre, University of Saskatchewan, Saskatoon; Thomas, A.G., and Wise, R.F., Agriculture Canada, Research Station, Regina, Saskatchewan.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report  [1585 KB pdf]  (No Appendices)

Associated SWEEP/LSP Research



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Completed: November, 1990

Key Words:

corn, soybeans, winter wheat, no-till, survey, weed species, weed density, conventional tillage, conservation tillage, herbicide


NOTE: Figures and Tables referred to here are only available in the hardcopy report.


Conservation tillage has been defined as any method of tillage which leaves a minimum of 30% plant residue on the soil surface. Such systems include no-till and various systems which reduce the number of tillages, or use different types of tillage equipment other than the moldboard plow. Adoption of conservation tillage systems in agriculture could significantly reduce erosion, soil degradation, and water pollution. 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.

Weed communities reflect farm management systems. As farm management systems change, for instance from conventional to conservation tillage, weed species composition and weed densities may change. Differences in the timing of weed emergence or in the rate of growth of weeds may also occur, which in turn will affect the success of weed management measures.

The transitional period during the conversion from conventional to conservation tillage may be particularly problematic, because the weed community is undergoing change. Weed problems may include those of both management systems. Conventional weed control practices must be adapted to new management systems.

Previous Surveys

Quantitative weed survey data are unavailable for most crops and regions in Ontario but a few studies have provided some information. Data on the distribution and abundance of weeds occurring in tomato and sweet corn fields of Essex, Kent, and Prince Edward Counties were published in 1964 by J. F. Alex (Weed Research 4:308-318). Corn, soybean, white bean, and mixed grain fields in Kent, Middlesex, and Perth Counties were surveyed by R. A. Richards (M.Sc. Thesis, University of Guelph, 1979). A survey of corn, soybean, cereal, and tomato fields in Essex and Kent Counties was also organized by A. S. Hamill during 1978 and 1979 (Publications 83-1 and 83-2 in the Weed Survey Series). In all these studies, only a small proportion of the province was included. Conventional tillage systems were assumed to have been used in these surveyed fields. Up-to-date quantitative data on weed populations under various tillage regimes throughout southern Ontario are needed.


The primary goal of the weed survey project, which is reported in this publication, is the identification of weed species likely to be the greatest problems under various tillage systems in southwestern Ontario. Information on the response of the weed community to changes in tillage practices is vital for a sensible farm management program. As well as the field survey for weeds, data on farm management practices were gathered through a questionnaire. This report is a summary of the results from 1988 and 1989.

Survey Area

The survey area is bounded by Lake Erie on the south and by the Detroit River, Lake St. Clair, St. Clair River, and Lake Huron on the west (Figure 1). The area extends north and east to 44 N latitude and to 80 W longitude. This southwestern corner of Ontario is part of the West St. Lawrence Lowland physiographic subdivision of Canada. All the area has been subjected to glacial erosion and deposition during the Pleistocene. Soils in the region are luvisols and gleysols, ranging in texture from sandy loam to clay, and formed on glacial till or lacustrine deposits. The topography varies from very gently undulating to rolling with elevations ranging from 175 m above sea level along Lake Erie to 500 m on the northern limit of the study area.

The survey included 11 counties of southwestern Ontario that are especially prone to soil erosion. These counties cover the watersheds of the west branch of the Hillman Creek, the Big Creek tributary of the Thames River, the Upper Little Ausable River, a tributary of the Maitland River, and Holiday Creek (Figure 2). These watersheds have erosion indices in access of 3 ton/ha/yr and are considered to be of high to medium erosion potential (L.J.P. Van Vliet, G.J. Wall, and W. T. Dickinson. 1978. Agricultural Watershed Studies).

The July mean temperature in the study area is 21 C and the January mean is -4 C. Mean annual minimum and maximum temperatures are -12 C and 35 C respectively. Corn heat units for the area range from 2300 to 3700. The mean annual total precipitation varies from 750 mm in the southwest to 950 mm in the north with a seasonal (May to September) potential evapotranspiration of approximately 500 mm in the study area. The annual frost-free season ranges from 150 days in the north to 180 days in the south.

Weather conditions for the two survey years are summarized in Tables 1 and 2. Temperatures were near normal for both years. The first year of the survey (1988) was generally dry throughout the survey area, especially in April, May, and June. The second year (1989) was wetter, especially in the extreme south of the region, where flooding often delayed seeding, or necessitated a second seeding operation.


Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)
This report takes a lot of the information that is found in SWEEP Report #19 and presents it in the Agriculture Canada Weed Survey Series format. The tables, figures and appendices contained in this publication contain the raw survey data that could not be included in Report #19. The results of the survey are detailed in the first section, the results of the questionnaire survey are in the second section and an appendix of field survey summary tables is found at the back.

The field survey was conducted after all spring and early summer herbicides had been applied so it reflects the weed populations which escaped control. Generally the survey found that the weed community did not change significantly among tillage systems but final overall densities were somewhat larger with less tillage.

The questionnaire results found the differences among management systems were minimal, therefore large scale changes in weed problems were not associated with the management systems.


The report contains a lot of information that could be further analyzed to give more insight into the weed populations and shifts in southwestern Ontario. The questionnaire provides useful information on herbicide usage, tillage implements used, number of tillage passes and timing of herbicide application.

Associated SWEEP/LSP Research:

  • SWEEP Report #19 - Studies on the Control of Problem Weed Species in Conservation Tillage Systems
  • 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 follow up surveys five years later.



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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 02:02:36 PM